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archived-ballistic/spec/arm64_xml/decp_r_p_r.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

<?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="decp_r_p_r" title="DECP (scalar)" type="instruction">
<docvars>
<docvar key="instr-class" value="sve" />
<docvar key="isa" value="A64" />
<docvar key="mnemonic" value="DECP" />
</docvars>
<heading>DECP (scalar)</heading>
<desc>
<brief>Decrement scalar by count of true predicate elements</brief>
<description>
<para>Counts the number of true elements in the source predicate and then uses the result to decrement the scalar destination.</para>
</description>
<status>Green</status>
<predicated>False</predicated>
<affected_by_sme output="general-purpose register" />
</desc>
<alias_list howmany="0"></alias_list>
<classes>
<iclass name="SVE" oneof="1" id="iclass_sve" no_encodings="1" isa="A64">
<docvars>
<docvar key="instr-class" value="sve" />
<docvar key="isa" value="A64" />
<docvar key="mnemonic" value="DECP" />
</docvars>
<iclassintro count="1"></iclassintro>
<regdiagram form="32" psname="DECP-R.P.R-_" tworows="1">
<box hibit="31" width="8" settings="8">
<c>0</c>
<c>0</c>
<c>1</c>
<c>0</c>
<c>0</c>
<c>1</c>
<c>0</c>
<c>1</c>
</box>
<box hibit="23" width="2" name="size" usename="1">
<c colspan="2"></c>
</box>
<box hibit="21" width="4" settings="4">
<c>1</c>
<c>0</c>
<c>1</c>
<c>1</c>
</box>
<box hibit="17" name="op" settings="1">
<c>0</c>
</box>
<box hibit="16" name="D" usename="1" settings="1">
<c>1</c>
</box>
<box hibit="15" width="5" settings="5">
<c>1</c>
<c>0</c>
<c>0</c>
<c>0</c>
<c>1</c>
</box>
<box hibit="10" name="opc2&lt;1&gt;" settings="1">
<c>0</c>
</box>
<box hibit="9" name="opc2&lt;0&gt;" settings="1">
<c>0</c>
</box>
<box hibit="8" width="4" name="Pm" usename="1">
<c colspan="4"></c>
</box>
<box hibit="4" width="5" name="Rdn" usename="1">
<c colspan="5"></c>
</box>
</regdiagram>
<encoding name="decp_r_p_r_" oneofinclass="1" oneof="1" label="">
<docvars>
<docvar key="instr-class" value="sve" />
<docvar key="isa" value="A64" />
<docvar key="mnemonic" value="DECP" />
</docvars>
<asmtemplate><text>DECP </text><a link="sa_xdn" hover="64-bit source and destination general-purpose register (field &quot;Rdn&quot;)">&lt;Xdn&gt;</a><text>, </text><a link="sa_pm" hover="Source scalable predicate register (field &quot;Pm&quot;)">&lt;Pm&gt;</a><text>.</text><a link="sa_t" hover="Size specifier (field &quot;size&quot;) [B,D,H,S]">&lt;T&gt;</a></asmtemplate>
</encoding>
<ps_section howmany="1">
<ps name="DECP-R.P.R-_" mylink="DECP-R.P.R-_" enclabels="" sections="1" secttype="noheading">
<pstext mayhavelinks="1" section="Decode" rep_section="decode">if !<a link="impl-aarch64.HaveSVE.0" file="shared_pseudocode.xml" hover="function: boolean HaveSVE()">HaveSVE</a>() &amp;&amp; !<a link="impl-aarch64.HaveSME.0" file="shared_pseudocode.xml" hover="function: boolean HaveSME()">HaveSME</a>() then UNDEFINED;
constant integer esize = 8 &lt;&lt; <a link="impl-shared.UInt.1" file="shared_pseudocode.xml" hover="function: integer UInt(bits(N) x)">UInt</a>(size);
integer m = <a link="impl-shared.UInt.1" file="shared_pseudocode.xml" hover="function: integer UInt(bits(N) x)">UInt</a>(Pm);
integer dn = <a link="impl-shared.UInt.1" file="shared_pseudocode.xml" hover="function: integer UInt(bits(N) x)">UInt</a>(Rdn);</pstext>
</ps>
</ps_section>
</iclass>
</classes>
<explanations scope="all">
<explanation enclist="decp_r_p_r_" symboldefcount="1">
<symbol link="sa_xdn">&lt;Xdn&gt;</symbol>
<account encodedin="Rdn">
<intro>
<para>Is the 64-bit name of the source and destination general-purpose register, encoded in the "Rdn" field.</para>
</intro>
</account>
</explanation>
<explanation enclist="decp_r_p_r_" symboldefcount="1">
<symbol link="sa_pm">&lt;Pm&gt;</symbol>
<account encodedin="Pm">
<intro>
<para>Is the name of the source scalable predicate register, encoded in the "Pm" field.</para>
</intro>
</account>
</explanation>
<explanation enclist="decp_r_p_r_" symboldefcount="1">
<symbol link="sa_t">&lt;T&gt;</symbol>
<definition encodedin="size">
<intro>Is the size specifier, </intro>
<table class="valuetable">
<tgroup cols="2">
<thead>
<row>
<entry class="bitfield">size</entry>
<entry class="symbol">&lt;T&gt;</entry>
</row>
</thead>
<tbody>
<row>
<entry class="bitfield">00</entry>
<entry class="symbol">B</entry>
</row>
<row>
<entry class="bitfield">01</entry>
<entry class="symbol">H</entry>
</row>
<row>
<entry class="bitfield">10</entry>
<entry class="symbol">S</entry>
</row>
<row>
<entry class="bitfield">11</entry>
<entry class="symbol">D</entry>
</row>
</tbody>
</tgroup>
</table>
</definition>
</explanation>
</explanations>
<ps_section howmany="1">
<ps name="DECP-R.P.R-_" mylink="execute" enclabels="" sections="1" secttype="Operation">
<pstext mayhavelinks="1" section="Execute" rep_section="execute"><a link="impl-aarch64.CheckSVEEnabled.0" file="shared_pseudocode.xml" hover="function: CheckSVEEnabled()">CheckSVEEnabled</a>();
constant integer VL = <a link="impl-aarch64.CurrentVL.read.none" file="shared_pseudocode.xml" hover="accessor: integer CurrentVL">CurrentVL</a>;
constant integer PL = VL DIV 8;
constant integer elements = VL DIV esize;
bits(64) operand1 = <a link="impl-aarch64.X.read.2" file="shared_pseudocode.xml" hover="accessor: bits(width) X[integer n, integer width]">X</a>[dn, 64];
bits(PL) operand2 = <a link="impl-aarch64.P.read.2" file="shared_pseudocode.xml" hover="accessor: bits(width) P[integer n, integer width]">P</a>[m, PL];
integer count = 0;
for e = 0 to elements-1
if <a link="impl-aarch64.ActivePredicateElement.3" file="shared_pseudocode.xml" hover="function: boolean ActivePredicateElement(bits(N) pred, integer e, integer esize)">ActivePredicateElement</a>(operand2, e, esize) then
count = count + 1;
<a link="impl-aarch64.X.write.2" file="shared_pseudocode.xml" hover="accessor: X[integer n, integer width] = bits(width) value">X</a>[dn, 64] = operand1 - count;</pstext>
</ps>
</ps_section>
</instructionsection>