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<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># String comparison: return 1 iff the two args passed in at the commandline are equal.</span>
<span id="L2" class="LineNr"> 2 </span><span class="subxComment">#</span>
<span id="L3" class="LineNr"> 3 </span><span class="subxComment"># To run (from the subx directory):</span>
<span id="L4" class="LineNr"> 4 </span><span class="subxComment"># $ subx translate examples/ex10.subx -o examples/ex10</span>
<span id="L5" class="LineNr"> 5 </span><span class="subxComment"># $ subx run examples/ex10 abc abd</span>
<span id="L6" class="LineNr"> 6 </span><span class="subxComment"># Expected result:</span>
<span id="L7" class="LineNr"> 7 </span><span class="subxComment"># $ echo $?</span>
<span id="L8" class="LineNr"> 8 </span><span class="subxComment"># 0 # false</span>
<span id="L9" class="LineNr"> 9 </span>
<span id="L10" class="LineNr">10 </span>== code
<span id="L11" class="LineNr">11 </span><span class="subxComment"># instruction effective address register displacement immediate</span>
<span id="L12" class="LineNr">12 </span><span class="subxS1Comment"># . op subop mod rm32 base index scale r32</span>
<span id="L13" class="LineNr">13 </span><span class="subxS1Comment"># . 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes</span>
<span id="L14" class="LineNr">14 </span>
<span id="L15" class="LineNr">15 </span><span class="subxComment"># main: return argv-equal(argv[1], argv[2])</span>
<span id="L16" class="LineNr">16 </span><span class="subxComment"># At the start of a SubX program:</span>
<span id="L17" class="LineNr">17 </span><span class="subxComment"># argc: *ESP</span>
<span id="L18" class="LineNr">18 </span><span class="subxComment"># argv[0]: *(ESP+4)</span>
<span id="L19" class="LineNr">19 </span><span class="subxComment"># argv[1]: *(ESP+8)</span>
<span id="L20" class="LineNr">20 </span><span class="subxComment"># ...</span>
<span id="L21" class="LineNr">21 </span> <span class="subxS1Comment"># . prolog</span>
<span id="L22" class="LineNr">22 </span> 89/copy 3/mod/direct 5/rm32/EBP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 4/r32/ESP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="subxComment"># copy ESP to EBP</span>
<span id="L23" class="LineNr">23 </span> <span class="subxComment"># argv-equal(argv[1], argv[2])</span>
<span id="L24" class="LineNr">24 </span> <span class="subxS2Comment"># . . push argv[2]</span>
<span id="L25" class="LineNr">25 </span> ff 6/subop/push 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0xc/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># push *(EBP+12)</span>
<span id="L26" class="LineNr">26 </span> <span class="subxS2Comment"># . . push argv[1]</span>
<span id="L27" class="LineNr">27 </span> ff 6/subop/push 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0x8/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># push *(EBP+8)</span>
<span id="L28" class="LineNr">28 </span> <span class="subxS2Comment"># . . call</span>
<span id="L29" class="LineNr">29 </span> e8/call argv-equal/disp32
<span id="L30" class="LineNr">30 </span> <span class="subxComment"># syscall(exit, EAX)</span>
<span id="L31" class="LineNr">31 </span> 89/copy 3/mod/direct 3/rm32/EBX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0/r32/EAX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="subxComment"># copy EAX to EBX</span>
<span id="L32" class="LineNr">32 </span> b8/copy-to-EAX 1/imm32
<span id="L33" class="LineNr">33 </span> cd/syscall 0x80/imm8
<span id="L34" class="LineNr">34 </span>
<span id="L35" class="LineNr">35 </span><span class="subxComment"># compare two null-terminated ascii strings</span>
<span id="L36" class="LineNr">36 </span><span class="subxComment"># reason for the name: the only place we should have null-terminated ascii strings is from commandline args</span>
<span id="L37" class="LineNr">37 </span>argv-equal: <span class="subxComment"># (s1, s2) : null-terminated ascii strings -> EAX : boolean</span>
<span id="L38" class="LineNr">38 </span> <span class="subxComment"># initialize s1 (ECX) and s2 (EDX)</span>
<span id="L39" class="LineNr">39 </span> 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none <span class="CommentedCode"> . </span> 1/r32/ECX 4/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># copy *(ESP+4) to ECX</span>
<span id="L40" class="LineNr">40 </span> 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none <span class="CommentedCode"> . </span> 2/r32/EDX 8/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># copy *(ESP+8) to EDX</span>
<span id="L41" class="LineNr">41 </span> <span class="subxComment"># while (true)</span>
<span id="L42" class="LineNr">42 </span>$argv-equal:loop:
<span id="L43" class="LineNr">43 </span> <span class="subxComment"># c1/EAX, c2/EBX = *s1, *s2</span>
<span id="L44" class="LineNr">44 </span> b8/copy-to-EAX 0/imm32
<span id="L45" class="LineNr">45 </span> 8a/copy 0/mod/indirect 1/rm32/ECX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0/r32/EAX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="subxComment"># copy byte at *ECX to lower byte of EAX</span>
<span id="L46" class="LineNr">46 </span> bb/copy-to-EBX 0/imm32
<span id="L47" class="LineNr">47 </span> 8a/copy 0/mod/indirect 2/rm32/EDX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 3/r32/EBX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="subxComment"># copy byte at *EDX to lower byte of EBX</span>
<span id="L48" class="LineNr">48 </span> <span class="subxComment"># if (c1 == 0) break</span>
<span id="L49" class="LineNr">49 </span> 3d/compare-EAX 0/imm32
<span id="L50" class="LineNr">50 </span> 74/jump-if-equal $argv-equal:break/disp8
<span id="L51" class="LineNr">51 </span> <span class="subxComment"># if (c1 != c2) return false</span>
<span id="L52" class="LineNr">52 </span> 39/compare 3/mod/direct 0/rm32/EAX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 3/r32/EBX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="subxComment"># compare EAX with EBX</span>
<span id="L53" class="LineNr">53 </span> 75/jump-if-not-equal $argv-equal:false/disp8
<span id="L54" class="LineNr">54 </span> <span class="subxComment"># ++s1, ++s2</span>
<span id="L55" class="LineNr">55 </span> 41/inc-ECX
<span id="L56" class="LineNr">56 </span> 42/inc-EDX
<span id="L57" class="LineNr">57 </span> <span class="subxComment"># end while</span>
<span id="L58" class="LineNr">58 </span> eb/jump $argv-equal:loop/disp8
<span id="L59" class="LineNr">59 </span>$argv-equal:break:
<span id="L60" class="LineNr">60 </span> <span class="subxComment"># if (c2 == 0) return true</span>
<span id="L61" class="LineNr">61 </span> 81 7/subop/compare 3/mod/direct 3/rm32/EBX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0/imm32 <span class="subxComment"># compare EBX</span>
<span id="L62" class="LineNr">62 </span> 75/jump-if-not-equal $argv-equal:false/disp8
<span id="L63" class="LineNr">63 </span>$argv-equal:success:
<span id="L64" class="LineNr">64 </span> b8/copy-to-EAX 1/imm32
<span id="L65" class="LineNr">65 </span> c3/return
<span id="L66" class="LineNr">66 </span> <span class="subxComment"># return false</span>
<span id="L67" class="LineNr">67 </span>$argv-equal:false:
<span id="L68" class="LineNr">68 </span> b8/copy-to-EAX 0/imm32
<span id="L69" class="LineNr">69 </span> c3/return
<span id="L70" class="LineNr">70 </span>
<span id="L71" class="LineNr">71 </span><span class="subxS2Comment"># . . vim:nowrap:textwidth=0</span>
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