From 21fbdce7aac04729f618819d3e117c3fd667ebc2 Mon Sep 17 00:00:00 2001
From: water111 <48171810+water111@users.noreply.github.com>
Date: Sun, 29 Nov 2020 18:01:30 -0500
Subject: [PATCH] [Compiler] Bitfield Types (#146)

* add the ability to define and read bitfield types

* new set

* add bitfield setting

* add static bitfields
---
 common/type_system/Type.cpp                   |  49 ++++++
 common/type_system/Type.h                     |  44 +++--
 common/type_system/TypeSystem.cpp             |  61 +++++++
 common/type_system/TypeSystem.h               |  16 ++
 common/type_system/deftype.cpp                | 139 ++++++++++++++-
 doc/changelog.md                              |   8 +-
 goalc/compiler/Compiler.h                     |  11 ++
 goalc/compiler/IR.cpp                         |  21 ++-
 goalc/compiler/IR.h                           |   4 +-
 goalc/compiler/Util.cpp                       |   4 +
 goalc/compiler/Val.cpp                        |  40 ++++-
 goalc/compiler/Val.h                          |  31 +++-
 goalc/compiler/compilation/Atoms.cpp          |   6 +-
 goalc/compiler/compilation/Define.cpp         | 162 ++++++++++--------
 goalc/compiler/compilation/Function.cpp       |   3 +
 goalc/compiler/compilation/Math.cpp           |  51 ++++++
 goalc/compiler/compilation/Static.cpp         |  83 +++++++++
 goalc/compiler/compilation/Type.cpp           |  22 ++-
 goalc/emitter/IGen.h                          |  15 +-
 .../arithmetic/shift-fixed.static.gc          |   2 +
 .../with_game/test-bitfield-access.gc         |  21 +++
 .../with_game/test-bitfield-tricky-access.gc  |  66 +++++++
 .../with_game/test-set-bitfield.gc            |  22 +++
 .../with_game/test-static-bitfield.gc         |  13 ++
 test/goalc/test_arithmetic.cpp                |   7 +-
 test/goalc/test_with_game.cpp                 |  18 ++
 26 files changed, 819 insertions(+), 100 deletions(-)
 create mode 100644 test/goalc/source_templates/arithmetic/shift-fixed.static.gc
 create mode 100644 test/goalc/source_templates/with_game/test-bitfield-access.gc
 create mode 100644 test/goalc/source_templates/with_game/test-bitfield-tricky-access.gc
 create mode 100644 test/goalc/source_templates/with_game/test-set-bitfield.gc
 create mode 100644 test/goalc/source_templates/with_game/test-static-bitfield.gc

diff --git a/common/type_system/Type.cpp b/common/type_system/Type.cpp
index 755f63ee01..541fc93da9 100644
--- a/common/type_system/Type.cpp
+++ b/common/type_system/Type.cpp
@@ -502,6 +502,15 @@ bool StructureType::operator==(const Type& other) const {
   // clang-format on
 }
 
+bool BitFieldType::operator==(const Type& other) const {
+  if (typeid(*this) != typeid(other)) {
+    return false;
+  }
+
+  auto* p_other = dynamic_cast<const BitFieldType*>(&other);
+  return other.is_equal(*this) && m_fields == p_other->m_fields;
+}
+
 int StructureType::get_size_in_memory() const {
   return m_size_in_mem;
 }
@@ -568,4 +577,44 @@ std::string BasicType::print() const {
 
 int BasicType::get_offset() const {
   return BASIC_OFFSET;
+}
+
+/////////////////
+// Bitfield
+/////////////////
+
+BitField::BitField(TypeSpec type, std::string name, int offset, int size)
+    : m_type(std::move(type)), m_name(std::move(name)), m_offset(offset), m_size(size) {}
+
+bool BitField::operator==(const BitField& other) const {
+  return m_type == other.m_type && m_name == other.m_name && m_offset == other.m_offset &&
+         other.m_size == m_size;
+}
+
+BitFieldType::BitFieldType(std::string parent, std::string name, int size, bool sign_extend)
+    : ValueType(std::move(parent), std::move(name), false, size, sign_extend, RegKind::GPR_64) {}
+
+bool BitFieldType::lookup_field(const std::string& name, BitField* out) const {
+  for (auto& field : m_fields) {
+    if (field.name() == name) {
+      *out = field;
+      return true;
+    }
+  }
+  return false;
+}
+
+std::string BitField::print() const {
+  return fmt::format("[{} {}] sz {} off {}", name(), type().print(), size(), offset());
+}
+
+std::string BitFieldType::print() const {
+  std::string result;
+  result += fmt::format("Parent type: {}\nFields:\n", get_parent());
+  for (auto& field : m_fields) {
+    result += fmt::format("  {}\n", field.print());
+  }
+  result += fmt::format("Mem size: {}, load size: {}, signed {}, align {}\n", get_size_in_memory(),
+                        get_load_size(), get_load_signed(), get_in_memory_alignment());
+  return result;
 }
\ No newline at end of file
diff --git a/common/type_system/Type.h b/common/type_system/Type.h
index 76af676556..081af6fb5b 100644
--- a/common/type_system/Type.h
+++ b/common/type_system/Type.h
@@ -174,12 +174,12 @@ class Field {
   void set_inline();
   std::string print() const;
   const TypeSpec& type() const { return m_type; }
-
   bool is_inline() const { return m_inline; }
-
   bool is_array() const { return m_array; }
-
   bool is_dynamic() const { return m_dynamic; }
+  const std::string& name() const { return m_name; }
+  int offset() const { return m_offset; }
+  bool operator==(const Field& other) const;
 
   int alignment() const {
     assert(m_alignment != -1);
@@ -191,17 +191,11 @@ class Field {
     return m_array_size;
   }
 
-  const std::string& name() const { return m_name; }
-
-  int offset() const { return m_offset; }
-
-  bool operator==(const Field& other) const;
-
  private:
   friend class TypeSystem;
   void set_alignment(int alignment) { m_alignment = alignment; }
-
   void set_offset(int offset) { m_offset = offset; }
+
   std::string m_name;
   TypeSpec m_type;
   int m_offset = -1;
@@ -260,8 +254,34 @@ class BasicType : public StructureType {
   ~BasicType() = default;
 };
 
-class BitField {};
+class BitField {
+ public:
+  BitField() = default;
+  BitField(TypeSpec type, std::string name, int offset, int size);
+  const std::string name() const { return m_name; }
+  int offset() const { return m_offset; }
+  int size() const { return m_size; }
+  const TypeSpec& type() const { return m_type; }
+  bool operator==(const BitField& other) const;
+  std::string print() const;
 
-class BitFieldType : ValueType {};
+ private:
+  TypeSpec m_type;
+  std::string m_name;
+  int m_offset = -1;  // in bits
+  int m_size = -1;    // in bits.
+};
+
+class BitFieldType : public ValueType {
+ public:
+  BitFieldType(std::string parent, std::string name, int size, bool sign_extend);
+  bool lookup_field(const std::string& name, BitField* out) const;
+  std::string print() const override;
+  bool operator==(const Type& other) const override;
+
+ private:
+  friend class TypeSystem;
+  std::vector<BitField> m_fields;
+};
 
 #endif  // JAK_TYPE_H
diff --git a/common/type_system/TypeSystem.cpp b/common/type_system/TypeSystem.cpp
index 6d8a31991b..e5c1ad5830 100644
--- a/common/type_system/TypeSystem.cpp
+++ b/common/type_system/TypeSystem.cpp
@@ -1307,4 +1307,65 @@ ReverseDerefInfo TypeSystem::get_reverse_deref_info(const ReverseDerefInputInfo&
   ReverseDerefInfo result;
   result.success = reverse_deref(input, &result.deref_path, &result.addr_of, &result.result_type);
   return result;
+}
+
+/*!
+ * Is the given type a bitfield type?
+ */
+bool TypeSystem::is_bitfield_type(const std::string& type_name) const {
+  return dynamic_cast<BitFieldType*>(lookup_type(type_name));
+}
+
+/*!
+ * Get information about a field within a bitfield type.
+ */
+BitfieldLookupInfo TypeSystem::lookup_bitfield_info(const std::string& type_name,
+                                                    const std::string& field_name) const {
+  auto type = get_type_of_type<BitFieldType>(type_name);
+  BitField f;
+  if (!type->lookup_field(field_name, &f)) {
+    fmt::print("[TypeSystem] Type {} has no bitfield named {}\n", type_name, field_name);
+    throw std::runtime_error("lookup_bitfield failed");
+  }
+
+  BitfieldLookupInfo result;
+  result.result_type = f.type();
+  result.offset = f.offset();
+  result.sign_extend = lookup_type(result.result_type)->get_load_signed();
+  result.size = f.size();
+  return result;
+}
+
+/*!
+ * Add a new field to a bitfield type.
+ * Set the field size to -1 if you want to just use the size of the type and not clip it.
+ */
+void TypeSystem::add_field_to_bitfield(BitFieldType* type,
+                                       const std::string& field_name,
+                                       const TypeSpec& field_type,
+                                       int offset,
+                                       int field_size) {
+  // in bits
+  auto load_size = lookup_type(field_type)->get_load_size() * 8;
+  if (field_size == -1) {
+    field_size = load_size;
+  }
+
+  if (field_size > load_size) {
+    fmt::print(
+        "[TypeSystem] Type {}'s bitfield {}'s set size is {}, which is larger than the actual "
+        "type: {}\n",
+        type->get_name(), field_name, field_size, load_size);
+    throw std::runtime_error("Failed to add bitfield to type");
+  }
+
+  if (field_size + offset > type->get_load_size() * 8) {
+    fmt::print(
+        "[TypeSystem] Type {}'s bitfield {} will run off the end of the type (ends at {} bits, "
+        "type is {} bits)\n",
+        type->get_name(), field_name, field_size + offset, type->get_load_size() * 8);
+    throw std::runtime_error("Failed to add bitfield to type");
+  }
+  BitField field(field_type, field_name, offset, field_size);
+  type->m_fields.push_back(field);
 }
\ No newline at end of file
diff --git a/common/type_system/TypeSystem.h b/common/type_system/TypeSystem.h
index d32c6de977..fd0f1adbfb 100644
--- a/common/type_system/TypeSystem.h
+++ b/common/type_system/TypeSystem.h
@@ -24,6 +24,13 @@ struct FieldLookupInfo {
   int array_size = -1;
 };
 
+struct BitfieldLookupInfo {
+  TypeSpec result_type;
+  int offset = -1;
+  int size = -1;
+  bool sign_extend = false;
+};
+
 struct DerefInfo {
   bool can_deref = false;
   bool mem_deref = false;
@@ -102,6 +109,8 @@ class TypeSystem {
 
   FieldLookupInfo lookup_field_info(const std::string& type_name,
                                     const std::string& field_name) const;
+  BitfieldLookupInfo lookup_bitfield_info(const std::string& type_name,
+                                          const std::string& field_name) const;
   void assert_field_offset(const std::string& type_name, const std::string& field_name, int offset);
   int add_field_to_type(StructureType* type,
                         const std::string& field_name,
@@ -122,6 +131,13 @@ class TypeSystem {
   std::vector<std::string> get_path_up_tree(const std::string& type);
   int get_next_method_id(Type* type);
 
+  bool is_bitfield_type(const std::string& type_name) const;
+  void add_field_to_bitfield(BitFieldType* type,
+                             const std::string& field_name,
+                             const TypeSpec& field_type,
+                             int offset,
+                             int field_size);
+
   /*!
    * Get a type by name and cast to a child class of Type*. Must succeed.
    */
diff --git a/common/type_system/deftype.cpp b/common/type_system/deftype.cpp
index d8965d3796..023f890d7c 100644
--- a/common/type_system/deftype.cpp
+++ b/common/type_system/deftype.cpp
@@ -136,7 +136,44 @@ void add_field(StructureType* structure, TypeSystem* ts, const goos::Object& def
   }
 }
 
-void declare_method(StructureType* type, TypeSystem* type_system, const goos::Object& def) {
+void add_bitfield(BitFieldType* bitfield_type, TypeSystem* ts, const goos::Object& def) {
+  auto rest = &def;
+
+  auto name = symbol_string(car(rest));
+  rest = cdr(rest);
+
+  auto type = parse_typespec(ts, car(rest));
+  rest = cdr(rest);
+
+  int offset_override = -1;
+  int size_override = -1;
+
+  if (!rest->is_empty_list()) {
+    while (!rest->is_empty_list()) {
+      auto opt_name = symbol_string(car(rest));
+      rest = cdr(rest);
+
+      if (opt_name == ":offset") {
+        offset_override = get_int(car(rest));
+        rest = cdr(rest);
+      } else if (opt_name == ":size") {
+        size_override = get_int(car(rest));
+        rest = cdr(rest);
+      } else {
+        throw std::runtime_error("Invalid option in field specification: " + opt_name);
+      }
+    }
+  }
+
+  if (offset_override == -1) {
+    throw std::runtime_error("Bitfield type must manually specify offsets always");
+  }
+
+  // it's fine if the size is -1, that means it'll just use the type's size.
+  ts->add_field_to_bitfield(bitfield_type, name, type, offset_override, size_override);
+}
+
+void declare_method(Type* type, TypeSystem* type_system, const goos::Object& def) {
   for_each_in_list(def, [&](const goos::Object& _obj) {
     auto obj = &_obj;
     // (name args return-type [id])
@@ -281,6 +318,97 @@ StructureDefResult parse_structure_def(StructureType* type,
   return result;
 }
 
+struct BitFieldTypeDefResult {
+  TypeFlags flags;
+  bool generate_runtime_type = true;
+};
+
+BitFieldTypeDefResult parse_bitfield_type_def(BitFieldType* type,
+                                              TypeSystem* ts,
+                                              const goos::Object& fields,
+                                              const goos::Object& options) {
+  BitFieldTypeDefResult result;
+  for_each_in_list(fields, [&](const goos::Object& o) { add_bitfield(type, ts, o); });
+  TypeFlags flags;
+  flags.heap_base = 0;
+  flags.size = type->get_size_in_memory();
+  flags.pad = 0;
+
+  auto* rest = &options;
+  int size_assert = -1;
+  int method_count_assert = -1;
+  uint64_t flag_assert = 0;
+  bool flag_assert_set = false;
+  while (!rest->is_empty_list()) {
+    if (car(rest).is_pair()) {
+      auto opt_list = &car(rest);
+      auto& first = car(opt_list);
+      opt_list = cdr(opt_list);
+
+      if (symbol_string(first) == ":methods") {
+        declare_method(type, ts, *opt_list);
+      } else {
+        throw std::runtime_error("Invalid option list in field specification: " +
+                                 car(rest).print());
+      }
+
+      rest = cdr(rest);
+    } else {
+      auto opt_name = symbol_string(car(rest));
+      rest = cdr(rest);
+
+      if (opt_name == ":size-assert") {
+        size_assert = get_int(car(rest));
+        if (size_assert == -1) {
+          throw std::runtime_error("Cannot use -1 as size-assert");
+        }
+        rest = cdr(rest);
+      } else if (opt_name == ":method-count-assert") {
+        method_count_assert = get_int(car(rest));
+        if (method_count_assert == -1) {
+          throw std::runtime_error("Cannot use -1 as method_count_assert");
+        }
+        rest = cdr(rest);
+      } else if (opt_name == ":flag-assert") {
+        flag_assert = get_int(car(rest));
+        flag_assert_set = true;
+        rest = cdr(rest);
+      } else if (opt_name == ":no-runtime-type") {
+        result.generate_runtime_type = false;
+      } else if (opt_name == ":heap-base") {
+        u16 hb = get_int(car(rest));
+        rest = cdr(rest);
+        flags.heap_base = hb;
+      } else {
+        throw std::runtime_error("Invalid option in field specification: " + opt_name);
+      }
+    }
+  }
+
+  if (size_assert != -1 && flags.size != u16(size_assert)) {
+    throw std::runtime_error("Type " + type->get_name() + " came out to size " +
+                             std::to_string(int(flags.size)) + " but size-assert was set to " +
+                             std::to_string(size_assert));
+  }
+
+  flags.methods = ts->get_next_method_id(type);
+
+  if (method_count_assert != -1 && flags.methods != u16(method_count_assert)) {
+    throw std::runtime_error(
+        "Type " + type->get_name() + " has " + std::to_string(int(flags.methods)) +
+        " methods, but method-count-assert was set to " + std::to_string(method_count_assert));
+  }
+
+  if (flag_assert_set && (flags.flag != flag_assert)) {
+    throw std::runtime_error(
+        fmt::format("Type {} has flag 0x{:x} but flag-assert was set to 0x{:x}", type->get_name(),
+                    flags.flag, flag_assert));
+  }
+
+  result.flags = flags;
+  return result;
+}
+
 }  // namespace
 
 TypeSpec parse_typespec(TypeSystem* type_system, const goos::Object& src) {
@@ -350,7 +478,14 @@ DeftypeResult parse_deftype(const goos::Object& deftype, TypeSystem* ts) {
     }
     ts->add_type(name, std::move(new_type));
   } else if (is_type("integer", parent_type, ts)) {
-    throw std::runtime_error("Creating a child type of integer is not supported yet.");
+    auto pto = ts->lookup_type(parent_type);
+    assert(pto);
+    auto new_type = std::make_unique<BitFieldType>(
+        parent_type_name, name, pto->get_size_in_memory(), pto->get_load_signed());
+    auto sr = parse_bitfield_type_def(new_type.get(), ts, field_list_obj, options_obj);
+    result.flags = sr.flags;
+    result.create_runtime_type = sr.generate_runtime_type;
+    ts->add_type(name, std::move(new_type));
   } else {
     throw std::runtime_error("Creating a child type from " + parent_type.print() +
                              " is not allowed or not supported yet.");
diff --git a/doc/changelog.md b/doc/changelog.md
index 53378171c2..e68ac41bb0 100644
--- a/doc/changelog.md
+++ b/doc/changelog.md
@@ -51,4 +51,10 @@
 ## V0.2
 - Breaking change: return type of a function using `return-from #f` to return a value from the entire function is now the lowest common ancestor of all possible return values.
 - Fixed bug where `return-from` could reach outside of an inlined function.
-- Fixed bug where `return-from` might not behave correctly when returning from inside a let inside an inlined function.
\ No newline at end of file
+- Fixed bug where `return-from` might not behave correctly when returning from inside a let inside an inlined function.
+- Added `fmin` and `fmax` floating point min and max. These work on multiple arguments and use the `minss`/`maxss` instructions for the best performance.
+- Added `imul64` instruction for doing a real 64-bit multiplication.  This must be used when porting code that looks at the `hi` register after an EE `mult`.
+- Added `shl`, `shr`, and `sar` shifts which take a constant integer. These cannot be used with a variable shift amount.
+- Added bitfield types to the type system
+- Added the ability to cast integers to bitfield types
+- Fixed a bug where casting between integer types with `the` that did not involve emitting code would permanently change the type of the variable.
\ No newline at end of file
diff --git a/goalc/compiler/Compiler.h b/goalc/compiler/Compiler.h
index 41c83a90d8..9ebd96cfb4 100644
--- a/goalc/compiler/Compiler.h
+++ b/goalc/compiler/Compiler.h
@@ -49,6 +49,8 @@ class Compiler {
   void init_logger();
   void init_settings();
   bool try_getting_macro_from_goos(const goos::Object& macro_name, goos::Object* dest);
+  void set_bitfield(const goos::Object& form, BitFieldVal* dst, RegVal* src, Env* env);
+  Val* do_set(const goos::Object& form, Val* dst, RegVal* src, Env* env);
   Val* compile_goos_macro(const goos::Object& o,
                           const goos::Object& macro_obj,
                           const goos::Object& rest,
@@ -89,6 +91,7 @@ class Compiler {
   bool is_quoted_sym(const goos::Object& o);
   bool is_basic(const TypeSpec& ts);
   bool is_structure(const TypeSpec& ts);
+  bool is_bitfield(const TypeSpec& ts);
   const goos::Object& pair_car(const goos::Object& o);
   const goos::Object& pair_cdr(const goos::Object& o);
   void expect_empty_list(const goos::Object& o);
@@ -134,6 +137,7 @@ class Compiler {
   bool is_none(Val* in);
 
   Val* compile_variable_shift(const RegVal* in, const RegVal* sa, Env* env, IntegerMathKind kind);
+  Val* compile_fixed_shift(const RegVal* in, u8 sa, Env* env, IntegerMathKind kind);
 
   Val* compile_format_string(const goos::Object& form,
                              Env* env,
@@ -160,6 +164,10 @@ class Compiler {
                                              const TypeSpec& type,
                                              const goos::Object& field_defs,
                                              Env* env);
+  Val* compile_new_static_bitfield(const goos::Object& form,
+                                   const TypeSpec& type,
+                                   const goos::Object& field_defs,
+                                   Env* env);
 
  public:
   // Atoms
@@ -225,6 +233,9 @@ class Compiler {
   Val* compile_shlv(const goos::Object& form, const goos::Object& rest, Env* env);
   Val* compile_sarv(const goos::Object& form, const goos::Object& rest, Env* env);
   Val* compile_shrv(const goos::Object& form, const goos::Object& rest, Env* env);
+  Val* compile_shl(const goos::Object& form, const goos::Object& rest, Env* env);
+  Val* compile_sar(const goos::Object& form, const goos::Object& rest, Env* env);
+  Val* compile_shr(const goos::Object& form, const goos::Object& rest, Env* env);
   Val* compile_mod(const goos::Object& form, const goos::Object& rest, Env* env);
   Val* compile_logxor(const goos::Object& form, const goos::Object& rest, Env* env);
   Val* compile_lognot(const goos::Object& form, const goos::Object& rest, Env* env);
diff --git a/goalc/compiler/IR.cpp b/goalc/compiler/IR.cpp
index 99e99ac484..b1ff333d50 100644
--- a/goalc/compiler/IR.cpp
+++ b/goalc/compiler/IR.cpp
@@ -392,6 +392,9 @@ void IR_FunctionAddr::do_codegen(emitter::ObjectGenerator* gen,
 IR_IntegerMath::IR_IntegerMath(IntegerMathKind kind, RegVal* dest, RegVal* arg)
     : m_kind(kind), m_dest(dest), m_arg(arg) {}
 
+IR_IntegerMath::IR_IntegerMath(IntegerMathKind kind, RegVal* dest, u8 shift_amount)
+    : m_kind(kind), m_dest(dest), m_shift_amount(shift_amount) {}
+
 std::string IR_IntegerMath::print() {
   switch (m_kind) {
     case IntegerMathKind::ADD_64:
@@ -412,6 +415,12 @@ std::string IR_IntegerMath::print() {
       return fmt::format("shlv {}, {}", m_dest->print(), m_arg->print());
     case IntegerMathKind::SHRV_64:
       return fmt::format("shrv {}, {}", m_dest->print(), m_arg->print());
+    case IntegerMathKind::SAR_64:
+      return fmt::format("sar {}, {}", m_dest->print(), m_shift_amount);
+    case IntegerMathKind::SHL_64:
+      return fmt::format("shl {}, {}", m_dest->print(), m_shift_amount);
+    case IntegerMathKind::SHR_64:
+      return fmt::format("shr {}, {}", m_dest->print(), m_shift_amount);
     case IntegerMathKind::AND_64:
       return fmt::format("and {}, {}", m_dest->print(), m_arg->print());
     case IntegerMathKind::OR_64:
@@ -430,7 +439,8 @@ RegAllocInstr IR_IntegerMath::to_rai() {
   rai.write.push_back(m_dest->ireg());
   rai.read.push_back(m_dest->ireg());
 
-  if (m_kind != IntegerMathKind::NOT_64) {
+  if (m_kind != IntegerMathKind::NOT_64 && m_kind != IntegerMathKind::SHL_64 &&
+      m_kind != IntegerMathKind::SAR_64 && m_kind != IntegerMathKind::SHR_64) {
     rai.read.push_back(m_arg->ireg());
   }
 
@@ -480,6 +490,15 @@ void IR_IntegerMath::do_codegen(emitter::ObjectGenerator* gen,
       gen->add_instr(IGen::sar_gpr64_cl(get_reg(m_dest, allocs, irec)), irec);
       assert(get_reg(m_arg, allocs, irec) == emitter::RCX);
       break;
+    case IntegerMathKind::SHL_64:
+      gen->add_instr(IGen::shl_gpr64_u8(get_reg(m_dest, allocs, irec), m_shift_amount), irec);
+      break;
+    case IntegerMathKind::SHR_64:
+      gen->add_instr(IGen::shr_gpr64_u8(get_reg(m_dest, allocs, irec), m_shift_amount), irec);
+      break;
+    case IntegerMathKind::SAR_64:
+      gen->add_instr(IGen::sar_gpr64_u8(get_reg(m_dest, allocs, irec), m_shift_amount), irec);
+      break;
     case IntegerMathKind::IMUL_32: {
       auto dr = get_reg(m_dest, allocs, irec);
       gen->add_instr(IGen::imul_gpr32_gpr32(dr, get_reg(m_arg, allocs, irec)), irec);
diff --git a/goalc/compiler/IR.h b/goalc/compiler/IR.h
index a79804c2d5..045746e29b 100644
--- a/goalc/compiler/IR.h
+++ b/goalc/compiler/IR.h
@@ -211,6 +211,7 @@ enum class IntegerMathKind {
 class IR_IntegerMath : public IR {
  public:
   IR_IntegerMath(IntegerMathKind kind, RegVal* dest, RegVal* arg);
+  IR_IntegerMath(IntegerMathKind kind, RegVal* dest, u8 shift_amount);
   std::string print() override;
   RegAllocInstr to_rai() override;
   void do_codegen(emitter::ObjectGenerator* gen,
@@ -221,7 +222,8 @@ class IR_IntegerMath : public IR {
  protected:
   IntegerMathKind m_kind;
   RegVal* m_dest;
-  RegVal* m_arg;
+  RegVal* m_arg = nullptr;
+  u8 m_shift_amount = 0;
 };
 
 enum class FloatMathKind { DIV_SS, MUL_SS, ADD_SS, SUB_SS, MIN_SS, MAX_SS };
diff --git a/goalc/compiler/Util.cpp b/goalc/compiler/Util.cpp
index 60aba59b7e..cf5866659f 100644
--- a/goalc/compiler/Util.cpp
+++ b/goalc/compiler/Util.cpp
@@ -150,6 +150,10 @@ bool Compiler::is_structure(const TypeSpec& ts) {
   return m_ts.typecheck(m_ts.make_typespec("structure"), ts, "", false, false);
 }
 
+bool Compiler::is_bitfield(const TypeSpec& ts) {
+  return m_ts.is_bitfield_type(ts.base_type());
+}
+
 bool Compiler::try_getting_constant_integer(const goos::Object& in, int64_t* out, Env* env) {
   (void)env;
   if (in.is_int()) {
diff --git a/goalc/compiler/Val.cpp b/goalc/compiler/Val.cpp
index 17c64cde81..ccd4105875 100644
--- a/goalc/compiler/Val.cpp
+++ b/goalc/compiler/Val.cpp
@@ -26,7 +26,6 @@ RegVal* Val::to_xmm(Env* fe) {
   if (rv->ireg().kind == emitter::RegKind::XMM) {
     return rv;
   } else {
-    assert(false);
     auto re = fe->make_xmm(coerce_to_reg_type(m_ts));
     fe->emit(std::make_unique<IR_RegSet>(re, rv));
     return re;
@@ -179,3 +178,42 @@ RegVal* StackVarAddrVal::to_reg(Env* fe) {
   fe->emit(std::make_unique<IR_GetStackAddr>(re, m_slot));
   return re;
 }
+
+std::string BitFieldVal::print() const {
+  return fmt::format("[bitfield sz {} off {} sx {} of {}]", m_size, m_offset, m_sign_extend,
+                     m_parent->print());
+}
+
+RegVal* BitFieldVal::to_reg(Env* env) {
+  // first get the parent value
+  auto parent_reg = m_parent->to_gpr(env);
+
+  auto fe = get_parent_env_of_type<FunctionEnv>(env);
+  auto result = fe->make_ireg(coerce_to_reg_type(m_ts), emitter::RegKind::GPR);
+  env->emit(std::make_unique<IR_RegSet>(result, parent_reg));
+
+  int start_bit = m_offset;
+  int end_bit = m_offset + m_size;
+  int epad = 64 - end_bit;
+  assert(epad >= 0);
+  int spad = start_bit;
+
+  // shift left as much as possible to kill upper bits
+  if (epad > 0) {
+    env->emit(std::make_unique<IR_IntegerMath>(IntegerMathKind::SHL_64, result, epad));
+  }
+
+  int next_shift = epad + spad;
+  assert(next_shift + m_size == 64);
+  assert(next_shift >= 0);
+
+  if (next_shift > 0) {
+    if (m_sign_extend) {
+      env->emit(std::make_unique<IR_IntegerMath>(IntegerMathKind::SAR_64, result, next_shift));
+    } else {
+      env->emit(std::make_unique<IR_IntegerMath>(IntegerMathKind::SHR_64, result, next_shift));
+    }
+  }
+
+  return result;
+}
\ No newline at end of file
diff --git a/goalc/compiler/Val.h b/goalc/compiler/Val.h
index 3e4c76eee6..e66d07aeb7 100644
--- a/goalc/compiler/Val.h
+++ b/goalc/compiler/Val.h
@@ -85,6 +85,7 @@ class RegVal : public Val {
 class SymbolVal : public Val {
  public:
   SymbolVal(std::string name, TypeSpec ts) : Val(std::move(ts)), m_name(std::move(name)) {
+    // this is for define, which looks at the SymbolVal and not the SymbolValueVal.
     mark_as_settable();
   }
   const std::string& name() const { return m_name; }
@@ -98,10 +99,14 @@ class SymbolVal : public Val {
 class SymbolValueVal : public Val {
  public:
   SymbolValueVal(const SymbolVal* sym, TypeSpec ts, bool sext)
-      : Val(std::move(ts)), m_sym(sym), m_sext(sext) {}
+      : Val(std::move(ts)), m_sym(sym), m_sext(sext) {
+    // this is for set, which looks at the Symbol's Value.
+    mark_as_settable();
+  }
   const std::string& name() const { return m_sym->name(); }
   std::string print() const override { return "[<" + name() + ">]"; }
   RegVal* to_reg(Env* fe) override;
+  const SymbolVal* sym() const { return m_sym; }
 
  protected:
   const SymbolVal* m_sym = nullptr;
@@ -240,6 +245,28 @@ class FloatConstantVal : public Val {
   StaticFloat* m_value = nullptr;
 };
 
-// Bitfield
+class BitFieldVal : public Val {
+ public:
+  BitFieldVal(TypeSpec ts, Val* parent, int offset, int size, bool sign_extend)
+      : Val(std::move(ts)),
+        m_parent(parent),
+        m_offset(offset),
+        m_size(size),
+        m_sign_extend(sign_extend) {
+    m_is_settable = parent->settable();
+  }
+  std::string print() const override;
+  RegVal* to_reg(Env* env) override;
+  int offset() const { return m_offset; }
+  int size() const { return m_size; }
+  bool sext() const { return m_sign_extend; }
+  Val* parent() { return m_parent; }
+
+ protected:
+  Val* m_parent = nullptr;
+  int m_offset = -1;
+  int m_size = -1;
+  bool m_sign_extend = false;
+};
 
 #endif  // JAK_VAL_H
diff --git a/goalc/compiler/compilation/Atoms.cpp b/goalc/compiler/compilation/Atoms.cpp
index 446105fbdb..39116eed86 100644
--- a/goalc/compiler/compilation/Atoms.cpp
+++ b/goalc/compiler/compilation/Atoms.cpp
@@ -106,9 +106,9 @@ static const std::unordered_map<
         {"shlv", &Compiler::compile_shlv},
         {"shrv", &Compiler::compile_shrv},
         {"sarv", &Compiler::compile_sarv},
-        //        {"shl", &Compiler::compile_shl},
-        //        {"shr", &Compiler::compile_shr},
-        //        {"sar", &Compiler::compile_sar},
+        {"shl", &Compiler::compile_shl},
+        {"shr", &Compiler::compile_shr},
+        {"sar", &Compiler::compile_sar},
         {"mod", &Compiler::compile_mod},
         {"logior", &Compiler::compile_logior},
         {"logxor", &Compiler::compile_logxor},
diff --git a/goalc/compiler/compilation/Define.cpp b/goalc/compiler/compilation/Define.cpp
index 1d04f5f41a..a225cdd065 100644
--- a/goalc/compiler/compilation/Define.cpp
+++ b/goalc/compiler/compilation/Define.cpp
@@ -88,6 +88,99 @@ Val* Compiler::compile_define_extern(const goos::Object& form, const goos::Objec
   return get_none();
 }
 
+void Compiler::set_bitfield(const goos::Object& form, BitFieldVal* dst, RegVal* src, Env* env) {
+  assert(!dst->sext());
+  auto fe = get_parent_env_of_type<FunctionEnv>(env);
+
+  // first, get the value we want to modify:
+  auto original_original = dst->parent()->to_gpr(env);
+  // let's not directly modify original, and instead create a copy then use do_set on parent.
+  // this way we avoid "cheating" the set system, although it should be safe...
+  auto original = fe->make_gpr(original_original->type());
+  env->emit(std::make_unique<IR_RegSet>(original, original_original));
+
+  // we'll need a temp register to hold a mask:
+  auto temp = fe->make_gpr(src->type());
+  // mask value should be 1's everywhere except for the field so we can AND with it
+  u64 mask_val = ~(((1 << dst->size()) - 1) << dst->offset());
+  env->emit(std::make_unique<IR_LoadConstant64>(temp, mask_val));
+  // modify the original!
+  env->emit(std::make_unique<IR_IntegerMath>(IntegerMathKind::AND_64, original, temp));
+
+  // put the source in temp
+  env->emit(std::make_unique<IR_RegSet>(temp, src));
+
+  // to shift us all the way to the left and clear upper bits
+  int left_shift_amnt = 64 - dst->size();
+  int right_shift_amnt = (64 - dst->size()) - dst->offset();
+  assert(right_shift_amnt >= 0);
+
+  if (left_shift_amnt > 0) {
+    env->emit(std::make_unique<IR_IntegerMath>(IntegerMathKind::SHL_64, temp, left_shift_amnt));
+  }
+
+  if (right_shift_amnt > 0) {
+    env->emit(std::make_unique<IR_IntegerMath>(IntegerMathKind::SHR_64, temp, right_shift_amnt));
+  }
+
+  env->emit(std::make_unique<IR_IntegerMath>(IntegerMathKind::OR_64, original, temp));
+  do_set(form, dst->parent(), original, env);
+}
+
+/*!
+ * The internal "set" logic.
+ */
+Val* Compiler::do_set(const goos::Object& form, Val* dest, RegVal* source, Env* env) {
+  if (!dest->settable()) {
+    throw_compile_error(form,
+                        "Tried to use set! on something that wasn't settable: " + dest->print());
+  }
+  auto as_mem_deref = dynamic_cast<MemoryDerefVal*>(dest);
+  auto as_pair = dynamic_cast<PairEntryVal*>(dest);
+  auto as_reg = dynamic_cast<RegVal*>(dest);
+  auto as_sym_val = dynamic_cast<SymbolValueVal*>(dest);
+  auto as_bitfield = dynamic_cast<BitFieldVal*>(dest);
+
+  if (as_mem_deref) {
+    // setting somewhere in memory
+    auto base = as_mem_deref->base;
+    auto base_as_mco = dynamic_cast<MemoryOffsetConstantVal*>(base);
+    if (base_as_mco) {
+      // if it is a constant offset, we can use a fancy x86-64 addressing mode to simplify
+      auto ti = m_ts.lookup_type(as_mem_deref->type());
+      env->emit(std::make_unique<IR_StoreConstOffset>(
+          source, base_as_mco->offset, base_as_mco->base->to_gpr(env), ti->get_load_size()));
+      return source;
+    } else {
+      // nope, the pointer to dereference is some compliated thing.
+      auto ti = m_ts.lookup_type(as_mem_deref->type());
+      env->emit(
+          std::make_unique<IR_StoreConstOffset>(source, 0, base->to_gpr(env), ti->get_load_size()));
+      return source;
+    }
+  } else if (as_pair) {
+    // this could probably be part of MemoryDerefVal and not a special case here.
+    env->emit(std::make_unique<IR_StoreConstOffset>(source, as_pair->is_car ? -2 : 2,
+                                                    as_pair->base->to_gpr(env), 4));
+    return source;
+  } else if (as_reg) {
+    typecheck(form, as_reg->type(), source->type(), "set! lexical variable");
+    env->emit(std::make_unique<IR_RegSet>(as_reg, source));
+    return source;
+  } else if (as_sym_val) {
+    typecheck(form, as_sym_val->type(), source->type(), "set! global symbol");
+    auto result_in_gpr = source->to_gpr(env);
+    env->emit(std::make_unique<IR_SetSymbolValue>(as_sym_val->sym(), result_in_gpr));
+    return result_in_gpr;
+  } else if (as_bitfield) {
+    set_bitfield(form, as_bitfield, source, env);
+    return get_none();
+  }
+
+  throw_compile_error(form, "Set not implemented for: " + dest->print());
+  return get_none();
+}
+
 /*!
  * Set something to something.
  * Lots of special cases.
@@ -101,71 +194,6 @@ Val* Compiler::compile_set(const goos::Object& form, const goos::Object& rest, E
   // and to_reg'd first, then the destination is computed, if the destination requires math to
   // compute.
   auto source = compile_error_guard(args.unnamed.at(1), env)->to_reg(env);
-
-  if (destination.is_symbol()) {
-    // destination is just a symbol, so it's either a lexical variable or a global.
-
-    // first, attempt a lexical set:
-    auto lex_place = env->lexical_lookup(destination);
-    if (lex_place) {
-      // typecheck and set!
-      typecheck(form, lex_place->type(), source->type(), "set! lexical variable");
-      env->emit(std::make_unique<IR_RegSet>(lex_place, source));
-      return source;
-    } else {
-      // try to set symbol
-      auto existing = m_symbol_types.find(destination.as_symbol()->name);
-      if (existing == m_symbol_types.end()) {
-        throw_compile_error(
-            form, "could not find something called " + symbol_string(destination) + " to set!");
-      } else {
-        typecheck(form, existing->second, source->type(), "set! global symbol");
-        auto fe = get_parent_env_of_type<FunctionEnv>(env);
-        auto sym_val =
-            fe->alloc_val<SymbolVal>(symbol_string(destination), m_ts.make_typespec("symbol"));
-        auto result_in_gpr = source->to_gpr(env);
-        if (!sym_val->settable()) {
-          throw_compile_error(
-              form, "Tried to use set! on something that wasn't settable: " + sym_val->print());
-        }
-        env->emit(std::make_unique<IR_SetSymbolValue>(sym_val, result_in_gpr));
-        return result_in_gpr;
-      }
-    }
-  } else {
-    // destination is some complex expression, so compile it and hopefully get something settable.
-    auto dest = compile_error_guard(destination, env);
-    if (!dest->settable()) {
-      throw_compile_error(form,
-                          "Tried to use set! on something that wasn't settable: " + dest->print());
-    }
-    auto as_mem_deref = dynamic_cast<MemoryDerefVal*>(dest);
-    auto as_pair = dynamic_cast<PairEntryVal*>(dest);
-    if (as_mem_deref) {
-      // setting somewhere in memory
-      auto base = as_mem_deref->base;
-      auto base_as_mco = dynamic_cast<MemoryOffsetConstantVal*>(base);
-      if (base_as_mco) {
-        // if it is a constant offset, we can use a fancy x86-64 addressing mode to simplify
-        auto ti = m_ts.lookup_type(as_mem_deref->type());
-        env->emit(std::make_unique<IR_StoreConstOffset>(
-            source, base_as_mco->offset, base_as_mco->base->to_gpr(env), ti->get_load_size()));
-        return source;
-      } else {
-        // nope, the pointer to dereference is some compliated thing.
-        auto ti = m_ts.lookup_type(as_mem_deref->type());
-        env->emit(std::make_unique<IR_StoreConstOffset>(source, 0, base->to_gpr(env),
-                                                        ti->get_load_size()));
-        return source;
-      }
-    } else if (as_pair) {
-      // this could probably be part of MemoryDerefVal and not a special case here.
-      env->emit(std::make_unique<IR_StoreConstOffset>(source, as_pair->is_car ? -2 : 2,
-                                                      as_pair->base->to_gpr(env), 4));
-      return source;
-    } else {
-      throw_compile_error(form, "Set not implemented for this yet");
-    }
-  }
-  throw std::runtime_error("Unexpected error in Set");
+  auto dest = compile_error_guard(destination, env);
+  return do_set(form, dest, source, env);
 }
\ No newline at end of file
diff --git a/goalc/compiler/compilation/Function.cpp b/goalc/compiler/compilation/Function.cpp
index 1807f865d4..a2eb5095ea 100644
--- a/goalc/compiler/compilation/Function.cpp
+++ b/goalc/compiler/compilation/Function.cpp
@@ -150,6 +150,7 @@ Val* Compiler::compile_lambda(const goos::Object& form, const goos::Object& rest
       IRegConstraint constr;
       constr.instr_idx = 0;  // constraint at function start
       auto ireg = new_func_env->make_ireg(lambda.params.at(i).type, emitter::RegKind::GPR);
+      ireg->mark_as_settable();
       constr.ireg = ireg->ireg();
       constr.desired_register = emitter::gRegInfo.get_arg_reg(i);
       new_func_env->params[lambda.params.at(i).name] = ireg;
@@ -350,6 +351,7 @@ Val* Compiler::compile_function_or_method_call(const goos::Object& form, Env* en
       auto type = eval_args.at(i)->type();
       auto copy = env->make_ireg(type, get_preferred_reg_kind(type));
       env->emit(std::make_unique<IR_RegSet>(copy, eval_args.at(i)));
+      copy->mark_as_settable();
       lexical_env->vars[head_as_lambda->lambda.params.at(i).name] = copy;
     }
 
@@ -494,6 +496,7 @@ Val* Compiler::compile_real_function_call(const goos::Object& form,
   std::vector<RegVal*> arg_outs;
   for (auto& arg : args) {
     arg_outs.push_back(env->make_ireg(arg->type(), emitter::RegKind::GPR));
+    arg_outs.back()->mark_as_settable();
     env->emit(std::make_unique<IR_RegSet>(arg_outs.back(), arg));
   }
 
diff --git a/goalc/compiler/compilation/Math.cpp b/goalc/compiler/compilation/Math.cpp
index fb05d60d49..749965406f 100644
--- a/goalc/compiler/compilation/Math.cpp
+++ b/goalc/compiler/compilation/Math.cpp
@@ -442,6 +442,57 @@ Val* Compiler::compile_variable_shift(const RegVal* in,
   return result;
 }
 
+Val* Compiler::compile_shl(const goos::Object& form, const goos::Object& rest, Env* env) {
+  auto args = get_va(form, rest);
+  va_check(form, args, {{}, {goos::ObjectType::INTEGER}}, {});
+  auto first = compile_error_guard(args.unnamed.at(0), env)->to_gpr(env);
+  auto sa = args.unnamed.at(1).as_int();
+  if (sa < 0 || sa > 64) {
+    throw_compile_error(form, "Cannot shift by more than 64, or by a negative amount");
+  }
+  return compile_fixed_shift(first, sa, env, IntegerMathKind::SHL_64);
+}
+
+Val* Compiler::compile_shr(const goos::Object& form, const goos::Object& rest, Env* env) {
+  auto args = get_va(form, rest);
+  va_check(form, args, {{}, {goos::ObjectType::INTEGER}}, {});
+  auto first = compile_error_guard(args.unnamed.at(0), env)->to_gpr(env);
+  auto sa = args.unnamed.at(1).as_int();
+  if (sa < 0 || sa > 64) {
+    throw_compile_error(form, "Cannot shift by more than 64, or by a negative amount");
+  }
+  return compile_fixed_shift(first, sa, env, IntegerMathKind::SHR_64);
+}
+
+Val* Compiler::compile_sar(const goos::Object& form, const goos::Object& rest, Env* env) {
+  auto args = get_va(form, rest);
+  va_check(form, args, {{}, {goos::ObjectType::INTEGER}}, {});
+  auto first = compile_error_guard(args.unnamed.at(0), env)->to_gpr(env);
+  auto sa = args.unnamed.at(1).as_int();
+  if (sa < 0 || sa > 64) {
+    throw_compile_error(form, "Cannot shift by more than 64, or by a negative amount");
+  }
+  return compile_fixed_shift(first, sa, env, IntegerMathKind::SAR_64);
+}
+
+Val* Compiler::compile_fixed_shift(const RegVal* in, u8 sa, Env* env, IntegerMathKind kind) {
+  // type check
+  if (get_math_mode(in->type()) != MathMode::MATH_INT) {
+    throw std::runtime_error("Can't shift a " + in->type().print());
+  }
+
+  if (sa > 64) {
+    throw std::runtime_error("Can't shift by more than 64");
+  }
+
+  // copy to result register
+  auto result = env->make_gpr(in->type());
+  env->emit(std::make_unique<IR_RegSet>(result, in));
+  // do the shift
+  env->emit(std::make_unique<IR_IntegerMath>(kind, result, sa));
+  return result;
+}
+
 Val* Compiler::compile_mod(const goos::Object& form, const goos::Object& rest, Env* env) {
   auto args = get_va(form, rest);
   va_check(form, args, {{}, {}}, {});
diff --git a/goalc/compiler/compilation/Static.cpp b/goalc/compiler/compilation/Static.cpp
index 12ec68a3a3..a7c40e4bcc 100644
--- a/goalc/compiler/compilation/Static.cpp
+++ b/goalc/compiler/compilation/Static.cpp
@@ -34,8 +34,91 @@ bool integer_fits(s64 in, int size, bool is_signed) {
       assert(false);
   }
 }
+
+u32 float_as_u32(float x) {
+  u32 result;
+  memcpy(&result, &x, 4);
+  return result;
+}
 }  // namespace
 
+Val* Compiler::compile_new_static_bitfield(const goos::Object& form,
+                                           const TypeSpec& type,
+                                           const goos::Object& _field_defs,
+                                           Env* env) {
+  auto fe = get_parent_env_of_type<FunctionEnv>(env);
+  u64 as_int = 0;
+
+  auto type_info = dynamic_cast<BitFieldType*>(m_ts.lookup_type(type));
+  assert(type_info);
+  assert(type_info->get_load_size() <= 8);
+
+  auto* field_defs = &_field_defs;
+  while (!field_defs->is_empty_list()) {
+    auto field_name_def = symbol_string(pair_car(*field_defs));
+    field_defs = &pair_cdr(*field_defs);
+
+    auto field_value = pair_car(*field_defs);
+    field_defs = &pair_cdr(*field_defs);
+
+    if (field_name_def.at(0) != ':') {
+      throw_compile_error(form,
+                          "expected field def name to start with :, instead got " + field_name_def);
+    }
+
+    field_name_def = field_name_def.substr(1);
+    auto field_info = m_ts.lookup_bitfield_info(type_info->get_name(), field_name_def);
+
+    auto field_offset = field_info.offset;
+    auto field_size = field_info.size;
+    assert(field_offset + field_size <= type_info->get_load_size() * 8);
+
+    if (is_integer(field_info.result_type)) {
+      s64 value = 0;
+      if (!try_getting_constant_integer(field_value, &value, env)) {
+        throw_compile_error(form,
+                            fmt::format("Field {} is an integer, but the value given couldn't be "
+                                        "converted to an integer at compile time.",
+                                        field_name_def));
+      }
+
+      // todo, check the integer fits!
+      u64 unsigned_value = value;
+      u64 or_value = unsigned_value;
+      // shift us all the way left to clear upper bits.
+      or_value <<= (64 - field_size);
+      // and back right.
+      or_value >>= (64 - field_size);
+      if (or_value != unsigned_value) {
+        throw_compile_error(form, fmt::format("Field {}'s value doesn't fit.", field_name_def));
+      }
+
+      as_int |= (or_value << field_offset);
+    } else if (is_float(field_info.result_type)) {
+      if (field_size != 32) {
+        throw_compile_error(form,
+                            fmt::format("Tried to put a float into a float bitfield that's not 4 "
+                                        "bytes. This is probably not what you wanted to do."));
+      }
+
+      float value = 0.f;
+      if (!try_getting_constant_float(field_value, &value, env)) {
+        throw_compile_error(form, fmt::format("Field {} is a float, but the value given couldn't "
+                                              "be converted to a float at compile time.",
+                                              field_name_def));
+      }
+      u64 float_value = float_as_u32(value);
+      as_int |= (float_value << field_offset);
+    }
+
+    else {
+      assert(false);  // for now
+    }
+  }
+
+  return fe->alloc_val<IntegerConstantVal>(type, as_int);
+}
+
 Val* Compiler::compile_new_static_structure_or_basic(const goos::Object& form,
                                                      const TypeSpec& type,
                                                      const goos::Object& _field_defs,
diff --git a/goalc/compiler/compilation/Type.cpp b/goalc/compiler/compilation/Type.cpp
index 4bd5855a44..3803e04aea 100644
--- a/goalc/compiler/compilation/Type.cpp
+++ b/goalc/compiler/compilation/Type.cpp
@@ -464,7 +464,13 @@ Val* Compiler::compile_deref(const goos::Object& form, const goos::Object& _rest
         continue;
       }
 
-      // todo try bitfield
+      auto bitfield_type = dynamic_cast<BitFieldType*>(type_info);
+      if (bitfield_type) {
+        auto bitfield_info = m_ts.lookup_bitfield_info(type_info->get_name(), field_name);
+        result = fe->alloc_val<BitFieldVal>(bitfield_info.result_type, result, bitfield_info.offset,
+                                            bitfield_info.size, bitfield_info.sign_extend);
+        continue;
+      }
     }
 
     auto index_value = compile_error_guard(field_obj, env)->to_gpr(env);
@@ -546,8 +552,13 @@ Val* Compiler::compile_the(const goos::Object& form, const goos::Object& rest, E
 
     if (m_ts.typecheck(m_ts.make_typespec("integer"), desired_ts, "", false, false)) {
       auto result = number_to_integer(base, env);
-      result->set_type(desired_ts);
-      return result;
+      if (result != base) {
+        result->set_type(desired_ts);
+        return result;
+      } else {
+        result = get_parent_env_of_type<FunctionEnv>(env)->alloc_val<AliasVal>(desired_ts, base);
+        return result;
+      }
     }
 
     if (m_ts.typecheck(m_ts.make_typespec("float"), desired_ts, "", false, false)) {
@@ -651,6 +662,11 @@ Val* Compiler::compile_new(const goos::Object& form, const goos::Object& _rest,
     if (is_structure(type_of_object)) {
       return compile_new_static_structure_or_basic(form, type_of_object, *rest, env);
     }
+
+    if (is_bitfield(type_of_object)) {
+      return compile_new_static_bitfield(form, type_of_object, *rest, env);
+    }
+
   } else if (allocation == "stack") {
     auto type_of_object = m_ts.make_typespec(type_as_string);
 
diff --git a/goalc/emitter/IGen.h b/goalc/emitter/IGen.h
index 111f34bf4f..a2b1132ea1 100644
--- a/goalc/emitter/IGen.h
+++ b/goalc/emitter/IGen.h
@@ -1528,9 +1528,10 @@ class IGen {
   /*!
    * Shift 64-ptr left (logical) by the constant shift amount "sa".
    */
-  static Instruction shl_gpr64_u8(uint8_t reg, uint8_t sa) {
+  static Instruction shl_gpr64_u8(Register reg, uint8_t sa) {
+    assert(reg.is_gpr());
     Instruction instr(0xc1);
-    instr.set_modrm_and_rex(4, reg, 3, true);
+    instr.set_modrm_and_rex(4, reg.hw_id(), 3, true);
     instr.set(Imm(1, sa));
     return instr;
   }
@@ -1538,9 +1539,10 @@ class IGen {
   /*!
    * Shift 64-ptr right (logical) by the constant shift amount "sa".
    */
-  static Instruction shr_gpr64_u8(uint8_t reg, uint8_t sa) {
+  static Instruction shr_gpr64_u8(Register reg, uint8_t sa) {
+    assert(reg.is_gpr());
     Instruction instr(0xc1);
-    instr.set_modrm_and_rex(5, reg, 3, true);
+    instr.set_modrm_and_rex(5, reg.hw_id(), 3, true);
     instr.set(Imm(1, sa));
     return instr;
   }
@@ -1548,9 +1550,10 @@ class IGen {
   /*!
    * Shift 64-ptr right (arithmetic) by the constant shift amount "sa".
    */
-  static Instruction sar_gpr64_u8(uint8_t reg, uint8_t sa) {
+  static Instruction sar_gpr64_u8(Register reg, uint8_t sa) {
+    assert(reg.is_gpr());
     Instruction instr(0xc1);
-    instr.set_modrm_and_rex(7, reg, 3, true);
+    instr.set_modrm_and_rex(7, reg.hw_id(), 3, true);
     instr.set(Imm(1, sa));
     return instr;
   }
diff --git a/test/goalc/source_templates/arithmetic/shift-fixed.static.gc b/test/goalc/source_templates/arithmetic/shift-fixed.static.gc
new file mode 100644
index 0000000000..3ea4f90d67
--- /dev/null
+++ b/test/goalc/source_templates/arithmetic/shift-fixed.static.gc
@@ -0,0 +1,2 @@
+(+ (shl 2 3) (shl 1 0) (shl 0 4) (shr 2 3) (shr 10 2) (shl -2 1) (sar -16 2))
+;; 16         1          0          0          2           -4          -4
\ No newline at end of file
diff --git a/test/goalc/source_templates/with_game/test-bitfield-access.gc b/test/goalc/source_templates/with_game/test-bitfield-access.gc
new file mode 100644
index 0000000000..6c236f0421
--- /dev/null
+++ b/test/goalc/source_templates/with_game/test-bitfield-access.gc
@@ -0,0 +1,21 @@
+(deftype test-bf-type (int32)
+  ((f1 int16 :offset 0)
+   (f2 uint8 :offset 16)
+   (f3 int8 :size 3 :offset 24)
+   (f4 uint8 :size 2 :offset 27)
+   (f5 int8 :size 2 :offset 29)
+   )
+  )
+
+(deftype test-bf-type2 (int64)
+  ((f1 int16 :offset 0)
+   (f2 uint8 :offset 16)
+   (f3 float :offset 24)
+   )
+  )
+
+(let ((temp (the test-bf-type #xf9f2f344))
+      (temp2 (the test-bf-type2 #x133f456789012345)))
+  (format #t "~A" (< (fabs (- 1.7711 (+ 1.0 (-> temp2 f3)))) 0.002))
+  (format #t "~X~X~X~X~X~%" (-> temp f1) (-> temp f2) (-> temp f3) (-> temp f4) (-> temp f5))
+  )
\ No newline at end of file
diff --git a/test/goalc/source_templates/with_game/test-bitfield-tricky-access.gc b/test/goalc/source_templates/with_game/test-bitfield-tricky-access.gc
new file mode 100644
index 0000000000..f8e99b430c
--- /dev/null
+++ b/test/goalc/source_templates/with_game/test-bitfield-tricky-access.gc
@@ -0,0 +1,66 @@
+(start-test "bitfield-tricky-access")
+
+(deftype bitfield-test-type-4 (uint32)
+  ((a uint8 :offset 3)
+   (b uint16 :offset 19 :size 12)
+   )
+  )
+
+(deftype bitfield-in-structure-type (structure)
+  ((a uint32 :offset 0)
+   (bitfield bitfield-test-type-4 :offset 0)
+   )
+  )
+
+;; check we can use a bitfield in a symbol
+(define *global-bitfield* (the bitfield-test-type-4 #x0))
+(set! (-> *global-bitfield* a) #xfe)
+(set! (-> *global-bitfield* b) #x12341234)
+
+(expect-eq #xfe (-> *global-bitfield* a))
+(expect-eq #x234 (-> *global-bitfield* b))
+(expect-eq #x11A007F0 (the uint *global-bitfield*))
+
+
+;; check we can use a bitfield as a field inside a structure
+(let ((heap-bitfield (new 'global 'bitfield-in-structure-type)))
+  (set! (-> heap-bitfield a) 0)
+  (set! (-> heap-bitfield bitfield a) #xfe)
+  (set! (-> heap-bitfield bitfield b) #x12341234)
+  (expect-eq #xfe (-> heap-bitfield bitfield a))
+  (expect-eq #x234 (-> heap-bitfield bitfield b))
+  (expect-eq #x11A007F0 (the uint (-> heap-bitfield bitfield)))
+  )
+
+
+(deftype bitfield-test-type-5 (uint32)
+  ((a uint8 :offset 0)
+   (b uint16 :offset 19 :size 12)
+   )
+  )
+
+;; check we can use a bitfield inside of a bitfield
+(deftype nested-bitfield (uint64)
+  ((a uint8 :offset 2 :size 3)
+   (bitfield bitfield-test-type-5 :offset 5)
+   )
+  )
+
+(let ((thing (the nested-bitfield #x0)))
+  (set! (-> thing a) #xfffff) ;; shoudlbe truncated to #b111
+  (expect-eq 7 (-> thing a))
+  (expect-eq 0 (-> thing bitfield a))
+  (set! (-> thing bitfield a ) #xffff) ;; truncated to #xff
+  (expect-eq #xff (-> thing bitfield a))
+  (expect-eq 7 (-> thing a))
+  )
+
+(define *global-nested-bitfield* (the nested-bitfield 0))
+  (set! (-> *global-nested-bitfield* a) #xfffff) ;; shoudlbe truncated to #b111
+  (expect-eq 7 (-> *global-nested-bitfield* a))
+  (expect-eq 0 (-> *global-nested-bitfield* bitfield a))
+  (set! (-> *global-nested-bitfield* bitfield a ) #xffff) ;; truncated to #xff
+  (expect-eq #xff (-> *global-nested-bitfield* bitfield a))
+  (expect-eq 7 (-> *global-nested-bitfield* a))
+
+(finish-test)
\ No newline at end of file
diff --git a/test/goalc/source_templates/with_game/test-set-bitfield.gc b/test/goalc/source_templates/with_game/test-set-bitfield.gc
new file mode 100644
index 0000000000..a55c58afa1
--- /dev/null
+++ b/test/goalc/source_templates/with_game/test-set-bitfield.gc
@@ -0,0 +1,22 @@
+
+
+(deftype test-bf-type3 (int64)
+  ((f1 uint16 :offset 0)
+   (f2 uint8 :size 7 :offset 16)
+   (f3 float :offset 23)
+   (f4 uint8 :size 1 :offset 55)
+   (f5 uint8 :offset 56)
+   )
+  )
+
+(let ((temp (the test-bf-type3 #x0)))
+  (set! (-> temp f1) #x12)
+  (set! (-> temp f2) #x13)
+  (set! (-> temp f3) 12.3433)
+  (set! (-> temp f4) #xffffffff) ; will get truncated.
+  (set! (-> temp f1) #x12)
+  (set! (-> temp f2) #x13)
+  (format #t "~A" (eq? 0 (-> temp f5))) ; check it gets truncated
+  (format #t "~f~%" (+ (-> temp f3) (-> temp f2) (-> temp f1) (-> temp f4)))
+  )
+
diff --git a/test/goalc/source_templates/with_game/test-static-bitfield.gc b/test/goalc/source_templates/with_game/test-static-bitfield.gc
new file mode 100644
index 0000000000..7ddaa837e0
--- /dev/null
+++ b/test/goalc/source_templates/with_game/test-static-bitfield.gc
@@ -0,0 +1,13 @@
+(deftype test-bf-type7 (int64)
+  ((f1 uint16 :offset 0)
+   (f2 uint8 :size 7 :offset 16)
+   (f3 float :offset 23)
+   (f4 uint8 :size 1 :offset 55)
+   (f5 uint8 :offset 56)
+   )
+  )
+
+(let ((temp (new 'static 'test-bf-type7 :f1 #x12 :f2 #x13 :f3 12.3433 :f4 #x1)))
+  (format #t "~A" (eq? 0 (-> temp f5))) ; check it gets truncated
+  (format #t "~f~%" (+ (-> temp f3) (-> temp f2) (-> temp f1) (-> temp f4)))
+  )
\ No newline at end of file
diff --git a/test/goalc/test_arithmetic.cpp b/test/goalc/test_arithmetic.cpp
index 1e7f18f07d..09d37b252f 100644
--- a/test/goalc/test_arithmetic.cpp
+++ b/test/goalc/test_arithmetic.cpp
@@ -227,10 +227,15 @@ TEST_F(ArithmeticTests, NestedFunctionCall) {
   runner.run_static_test(env, testCategory, "nested-function.static.gc", {"10\n"});
 }
 
-TEST_F(ArithmeticTests, ShiftOperations) {
+TEST_F(ArithmeticTests, VariableShift) {
   runner.run_static_test(env, testCategory, "shiftvs.static.gc", {"11\n"});
 }
 
+TEST_F(ArithmeticTests, FixedShift) {
+  // same math as the variable shift test, just using the fixed shift operators.
+  runner.run_static_test(env, testCategory, "shift-fixed.static.gc", {"11\n"});
+}
+
 TEST_F(ArithmeticTests, Subtraction) {
   runner.run_static_test(env, testCategory, "subtract-1.static.gc", {"4\n"});
   runner.run_static_test(env, testCategory, "subtract-2.static.gc", {"4\n"});
diff --git a/test/goalc/test_with_game.cpp b/test/goalc/test_with_game.cpp
index 9f4a980c4e..34dffd2aeb 100644
--- a/test/goalc/test_with_game.cpp
+++ b/test/goalc/test_with_game.cpp
@@ -302,6 +302,24 @@ TEST_F(WithGameTests, GameCount) {
                          get_test_pass_string("game-count", 4));
 }
 
+TEST_F(WithGameTests, BitFieldAccess) {
+  runner.run_static_test(env, testCategory, "test-bitfield-access.gc",
+                         {"#tfffffffffffff344f213ffffffffffffffff\n0\n"});
+}
+
+TEST_F(WithGameTests, SimpleBitField) {
+  runner.run_static_test(env, testCategory, "test-set-bitfield.gc", {"#t50.3432\n0\n"});
+}
+
+TEST_F(WithGameTests, StaticBitField) {
+  runner.run_static_test(env, testCategory, "test-static-bitfield.gc", {"#t50.3432\n0\n"});
+}
+
+TEST_F(WithGameTests, TrickyBitField) {
+  runner.run_static_test(env, testCategory, "test-bitfield-tricky-access.gc",
+                         get_test_pass_string("bitfield-tricky-access", 14));
+}
+
 TEST_F(WithGameTests, Math) {
   runner.run_static_test(env, testCategory, "test-math.gc", get_test_pass_string("math", 31));
 }