From 4fa140ec32b8f1bdb82b63a7799a3564d2ad5681 Mon Sep 17 00:00:00 2001
From: Cameron McCormack <cam@mcc.id.au>
Date: Tue, 20 Oct 2015 10:16:19 +1100
Subject: [PATCH] Bug 1216038 - Deduce underlying integer type for
 MakeEnumeratedRange starting at 0. r=froydnj

---
 mfbt/EnumeratedRange.h | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/mfbt/EnumeratedRange.h b/mfbt/EnumeratedRange.h
index 2fd0f881f1f9..109d8dd9d121 100644
--- a/mfbt/EnumeratedRange.h
+++ b/mfbt/EnumeratedRange.h
@@ -171,6 +171,9 @@ private:
 #endif
 
 // Create a range to iterate from aBegin to aEnd, exclusive.
+//
+// (Once we can rely on std::underlying_type, we can remove the IntType
+// template parameter.)
 template<typename IntType, typename EnumType>
 inline detail::EnumeratedRange<IntType, EnumType>
 MakeEnumeratedRange(EnumType aBegin, EnumType aEnd)
@@ -189,11 +192,15 @@ MakeEnumeratedRange(EnumType aBegin, EnumType aEnd)
 
 // Create a range to iterate from EnumType(0) to aEnd, exclusive. EnumType(0)
 // should exist, but note that there is no way for us to ensure that it does!
-template<typename IntType, typename EnumType>
-inline detail::EnumeratedRange<IntType, EnumType>
+// Since the enumeration starts at EnumType(0), we know for sure that the values
+// will be in range of our deduced IntType.
+template<typename EnumType>
+inline detail::EnumeratedRange<UnsignedStdintTypeForSize<sizeof(EnumType)>::Type,
+                               EnumType>
 MakeEnumeratedRange(EnumType aEnd)
 {
-  return MakeEnumeratedRange<IntType>(EnumType(0), aEnd);
+  return MakeEnumeratedRange<UnsignedStdintTypeForSize<sizeof(EnumType)>::Type>(
+      EnumType(0), aEnd);
 }
 
 #ifdef __GNUC__