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archived-ballistic/spec/arm64_xml/fcsel_float.xml
Ronald Caesar 26a677f8b4 decoder: Add ARM specification docs
Signed-off-by: Ronald Caesar <github43132@proton.me>
2025-12-12 18:11:36 -04:00

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<?xml version="1.0" encoding="utf-8"?>
<?xml-stylesheet type="text/xsl" encoding="UTF-8" href="iform.xsl" version="1.0"?>
<!DOCTYPE instructionsection PUBLIC "-//ARM//DTD instructionsection //EN" "iform-p.dtd">
<!-- Copyright (c) 2010-2022 Arm Limited or its affiliates. All rights reserved. -->
<!-- This document is Non-Confidential. This document may only be used and distributed in accordance with the terms of the agreement entered into by Arm and the party that Arm delivered this document to. -->
<instructionsection id="FCSEL_float" title="FCSEL -- A64" type="instruction">
<docvars>
<docvar key="instr-class" value="float" />
<docvar key="isa" value="A64" />
<docvar key="mnemonic" value="FCSEL" />
</docvars>
<heading>FCSEL</heading>
<desc>
<brief>
<para>Floating-point Conditional Select (scalar)</para>
</brief>
<authored>
<para>Floating-point Conditional Select (scalar). This instruction allows the SIMD&amp;FP destination register to take the value from either one or the other of two SIMD&amp;FP source registers. If the condition passes, the first SIMD&amp;FP source register value is taken, otherwise the second SIMD&amp;FP source register value is taken.</para>
<para>Depending on the settings in the <xref linkend="AArch64.cpacr_el1">CPACR_EL1</xref>, <xref linkend="AArch64.cptr_el2">CPTR_EL2</xref>, and <xref linkend="AArch64.cptr_el3">CPTR_EL3</xref> registers, and the current Security state and Exception level, an attempt to execute the instruction might be trapped.</para>
</authored>
</desc>
<operationalnotes>
<para>If PSTATE.DIT is 1:</para>
<list type="unordered">
<listitem><content>The execution time of this instruction is independent of:<list type="unordered"><listitem><content>The values of the data supplied in any of its registers.</content></listitem><listitem><content>The values of the NZCV flags.</content></listitem></list></content></listitem>
<listitem><content>The response of this instruction to asynchronous exceptions does not vary based on:<list type="unordered"><listitem><content>The values of the data supplied in any of its registers.</content></listitem><listitem><content>The values of the NZCV flags.</content></listitem></list></content></listitem>
</list>
</operationalnotes>
<alias_list howmany="0"></alias_list>
<classes>
<iclass name="Floating-point" oneof="1" id="iclass_float" no_encodings="3" isa="A64">
<docvars>
<docvar key="instr-class" value="float" />
<docvar key="isa" value="A64" />
<docvar key="mnemonic" value="FCSEL" />
</docvars>
<iclassintro count="3"></iclassintro>
<regdiagram form="32" psname="aarch64/instrs/float/move/fp/select">
<box hibit="31" name="M" settings="1">
<c>0</c>
</box>
<box hibit="30" settings="1">
<c>0</c>
</box>
<box hibit="29" name="S" settings="1">
<c>0</c>
</box>
<box hibit="28" width="5" settings="5">
<c>1</c>
<c>1</c>
<c>1</c>
<c>1</c>
<c>0</c>
</box>
<box hibit="23" width="2" name="ftype" usename="1">
<c colspan="2"></c>
</box>
<box hibit="21" settings="1">
<c>1</c>
</box>
<box hibit="20" width="5" name="Rm" usename="1">
<c colspan="5"></c>
</box>
<box hibit="15" width="4" name="cond" usename="1">
<c colspan="4"></c>
</box>
<box hibit="11" width="2" settings="2">
<c>1</c>
<c>1</c>
</box>
<box hibit="9" width="5" name="Rn" usename="1">
<c colspan="5"></c>
</box>
<box hibit="4" width="5" name="Rd" usename="1">
<c colspan="5"></c>
</box>
</regdiagram>
<encoding name="FCSEL_H_floatsel" oneofinclass="3" oneof="3" label="Half-precision" bitdiffs="ftype == 11">
<docvars>
<docvar key="datatype" value="half" />
<docvar key="instr-class" value="float" />
<docvar key="isa" value="A64" />
<docvar key="mnemonic" value="FCSEL" />
</docvars>
<arch_variants>
<arch_variant name="ARMv8.2" feature="FEAT_FP16" />
</arch_variants>
<box hibit="23" width="2" name="ftype">
<c>1</c>
<c>1</c>
</box>
<asmtemplate><text>FCSEL </text><a link="sa_hd" hover="16-bit SIMD&amp;FP destination register (field &quot;Rd&quot;)">&lt;Hd&gt;</a><text>, </text><a link="sa_hn" hover="First 16-bit SIMD&amp;FP source register (field &quot;Rn&quot;)">&lt;Hn&gt;</a><text>, </text><a link="sa_hm" hover="Second 16-bit SIMD&amp;FP source register (field &quot;Rm&quot;)">&lt;Hm&gt;</a><text>, </text><a link="sa_cond" hover="Standard condition (field &quot;cond&quot;)">&lt;cond&gt;</a></asmtemplate>
</encoding>
<encoding name="FCSEL_S_floatsel" oneofinclass="3" oneof="3" label="Single-precision" bitdiffs="ftype == 00">
<docvars>
<docvar key="datatype" value="single" />
<docvar key="instr-class" value="float" />
<docvar key="isa" value="A64" />
<docvar key="mnemonic" value="FCSEL" />
</docvars>
<box hibit="23" width="2" name="ftype">
<c>0</c>
<c>0</c>
</box>
<asmtemplate><text>FCSEL </text><a link="sa_sd" hover="32-bit SIMD&amp;FP destination register (field &quot;Rd&quot;)">&lt;Sd&gt;</a><text>, </text><a link="sa_sn" hover="First 32-bit SIMD&amp;FP source register (field &quot;Rn&quot;)">&lt;Sn&gt;</a><text>, </text><a link="sa_sm" hover="Second 32-bit SIMD&amp;FP source register (field &quot;Rm&quot;)">&lt;Sm&gt;</a><text>, </text><a link="sa_cond" hover="Standard condition (field &quot;cond&quot;)">&lt;cond&gt;</a></asmtemplate>
</encoding>
<encoding name="FCSEL_D_floatsel" oneofinclass="3" oneof="3" label="Double-precision" bitdiffs="ftype == 01">
<docvars>
<docvar key="datatype" value="double" />
<docvar key="instr-class" value="float" />
<docvar key="isa" value="A64" />
<docvar key="mnemonic" value="FCSEL" />
</docvars>
<box hibit="23" width="2" name="ftype">
<c>0</c>
<c>1</c>
</box>
<asmtemplate><text>FCSEL </text><a link="sa_dd" hover="64-bit SIMD&amp;FP destination register (field &quot;Rd&quot;)">&lt;Dd&gt;</a><text>, </text><a link="sa_dn" hover="First 64-bit SIMD&amp;FP source register (field &quot;Rn&quot;)">&lt;Dn&gt;</a><text>, </text><a link="sa_dm" hover="Second 64-bit SIMD&amp;FP source register (field &quot;Rm&quot;)">&lt;Dm&gt;</a><text>, </text><a link="sa_cond" hover="Standard condition (field &quot;cond&quot;)">&lt;cond&gt;</a></asmtemplate>
</encoding>
<ps_section howmany="1">
<ps name="aarch64/instrs/float/move/fp/select" mylink="aarch64.instrs.float.move.fp.select" enclabels="" sections="1" secttype="noheading">
<pstext mayhavelinks="1" section="Decode" rep_section="decode">integer d = <a link="impl-shared.UInt.1" file="shared_pseudocode.xml" hover="function: integer UInt(bits(N) x)">UInt</a>(Rd);
integer n = <a link="impl-shared.UInt.1" file="shared_pseudocode.xml" hover="function: integer UInt(bits(N) x)">UInt</a>(Rn);
integer m = <a link="impl-shared.UInt.1" file="shared_pseudocode.xml" hover="function: integer UInt(bits(N) x)">UInt</a>(Rm);
integer datasize;
case ftype of
when '00' datasize = 32;
when '01' datasize = 64;
when '10' UNDEFINED;
when '11'
if <a link="impl-shared.HaveFP16Ext.0" file="shared_pseudocode.xml" hover="function: boolean HaveFP16Ext()">HaveFP16Ext</a>() then
datasize = 16;
else
UNDEFINED;
bits(4) condition = cond;</pstext>
</ps>
</ps_section>
</iclass>
</classes>
<explanations scope="all">
<explanation enclist="FCSEL_D_floatsel" symboldefcount="1">
<symbol link="sa_dd">&lt;Dd&gt;</symbol>
<account encodedin="Rd">
<intro>
<para>Is the 64-bit name of the SIMD&amp;FP destination register, encoded in the "Rd" field.</para>
</intro>
</account>
</explanation>
<explanation enclist="FCSEL_D_floatsel" symboldefcount="1">
<symbol link="sa_dn">&lt;Dn&gt;</symbol>
<account encodedin="Rn">
<intro>
<para>Is the 64-bit name of the first SIMD&amp;FP source register, encoded in the "Rn" field.</para>
</intro>
</account>
</explanation>
<explanation enclist="FCSEL_D_floatsel" symboldefcount="1">
<symbol link="sa_dm">&lt;Dm&gt;</symbol>
<account encodedin="Rm">
<intro>
<para>Is the 64-bit name of the second SIMD&amp;FP source register, encoded in the "Rm" field.</para>
</intro>
</account>
</explanation>
<explanation enclist="FCSEL_H_floatsel" symboldefcount="1">
<symbol link="sa_hd">&lt;Hd&gt;</symbol>
<account encodedin="Rd">
<intro>
<para>Is the 16-bit name of the SIMD&amp;FP destination register, encoded in the "Rd" field.</para>
</intro>
</account>
</explanation>
<explanation enclist="FCSEL_H_floatsel" symboldefcount="1">
<symbol link="sa_hn">&lt;Hn&gt;</symbol>
<account encodedin="Rn">
<intro>
<para>Is the 16-bit name of the first SIMD&amp;FP source register, encoded in the "Rn" field.</para>
</intro>
</account>
</explanation>
<explanation enclist="FCSEL_H_floatsel" symboldefcount="1">
<symbol link="sa_hm">&lt;Hm&gt;</symbol>
<account encodedin="Rm">
<intro>
<para>Is the 16-bit name of the second SIMD&amp;FP source register, encoded in the "Rm" field.</para>
</intro>
</account>
</explanation>
<explanation enclist="FCSEL_S_floatsel" symboldefcount="1">
<symbol link="sa_sd">&lt;Sd&gt;</symbol>
<account encodedin="Rd">
<intro>
<para>Is the 32-bit name of the SIMD&amp;FP destination register, encoded in the "Rd" field.</para>
</intro>
</account>
</explanation>
<explanation enclist="FCSEL_S_floatsel" symboldefcount="1">
<symbol link="sa_sn">&lt;Sn&gt;</symbol>
<account encodedin="Rn">
<intro>
<para>Is the 32-bit name of the first SIMD&amp;FP source register, encoded in the "Rn" field.</para>
</intro>
</account>
</explanation>
<explanation enclist="FCSEL_S_floatsel" symboldefcount="1">
<symbol link="sa_sm">&lt;Sm&gt;</symbol>
<account encodedin="Rm">
<intro>
<para>Is the 32-bit name of the second SIMD&amp;FP source register, encoded in the "Rm" field.</para>
</intro>
</account>
</explanation>
<explanation enclist="FCSEL_D_floatsel, FCSEL_H_floatsel, FCSEL_S_floatsel" symboldefcount="1">
<symbol link="sa_cond">&lt;cond&gt;</symbol>
<account encodedin="cond">
<intro>
<para>Is one of the standard conditions, encoded in the "cond" field in the standard way.</para>
</intro>
</account>
</explanation>
</explanations>
<ps_section howmany="1">
<ps name="aarch64/instrs/float/move/fp/select" mylink="execute" enclabels="" sections="1" secttype="Operation">
<pstext mayhavelinks="1" section="Execute" rep_section="execute"><a link="impl-aarch64.CheckFPEnabled64.0" file="shared_pseudocode.xml" hover="function: CheckFPEnabled64()">CheckFPEnabled64</a>();
bits(datasize) result;
result = if <a link="impl-shared.ConditionHolds.1" file="shared_pseudocode.xml" hover="function: boolean ConditionHolds(bits(4) cond)">ConditionHolds</a>(condition) then <a link="impl-aarch64.V.read.2" file="shared_pseudocode.xml" hover="accessor: bits(width) V[integer n, integer width]">V</a>[n, datasize] else <a link="impl-aarch64.V.read.2" file="shared_pseudocode.xml" hover="accessor: bits(width) V[integer n, integer width]">V</a>[m, datasize];
<a link="impl-aarch64.V.write.2" file="shared_pseudocode.xml" hover="accessor: V[integer n, integer width] = bits(width) value">V</a>[d, datasize] = result;</pstext>
</ps>
</ps_section>
</instructionsection>