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<title>Mu - 112read-byte.subx</title>
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<a href='https://github.com/akkartik/mu/blob/main/112read-byte.subx'>https://github.com/akkartik/mu/blob/main/112read-byte.subx</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr">  1 </span><span class="subxComment"># Read a single byte from a stream.</span>
<span id="L2" class="LineNr">  2 </span><span class="subxComment">#</span>
<span id="L3" class="LineNr">  3 </span><span class="subxComment"># We need to do this in machine code because streams need to be opaque types,</span>
<span id="L4" class="LineNr">  4 </span><span class="subxComment"># and we don't yet support opaque types in Mu.</span>
<span id="L5" class="LineNr">  5 </span>
<span id="L6" class="LineNr">  6 </span>== code
<span id="L7" class="LineNr">  7 </span><span class="subxComment">#   instruction                     effective address                                                   register    displacement    immediate</span>
<span id="L8" class="LineNr">  8 </span><span class="subxS1Comment"># . op          subop               mod             rm32          base        index         scale       r32</span>
<span id="L9" class="LineNr">  9 </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="L10" class="LineNr"> 10 </span>
<span id="L11" class="LineNr"> 11 </span><span class="subxComment"># Return next byte value in eax, with top 3 bytes cleared.</span>
<span id="L12" class="LineNr"> 12 </span><span class="subxComment"># Abort on reaching end of stream.</span>
<span id="L13" class="LineNr"> 13 </span><span class="subxFunction">read-byte</span>:  <span class="subxComment"># s: (addr stream byte) -&gt; result/eax: byte</span>
<span id="L14" class="LineNr"> 14 </span>    <span class="subxS1Comment"># . prologue</span>
<span id="L15" class="LineNr"> 15 </span>    55/push-ebp
<span id="L16" class="LineNr"> 16 </span>    89/copy                         3/mod/direct    5/rm32/ebp   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          4/r32/esp  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># copy esp to ebp</span>
<span id="L17" class="LineNr"> 17 </span>    <span class="subxS1Comment"># . save registers</span>
<span id="L18" class="LineNr"> 18 </span>    51/push-ecx
<span id="L19" class="LineNr"> 19 </span>    56/push-esi
<span id="L20" class="LineNr"> 20 </span>    <span class="subxComment"># esi = s</span>
<span id="L21" class="LineNr"> 21 </span>    8b/copy                         1/mod/*+disp8   5/rm32/ebp   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          6/r32/esi   8/disp8        <span class="Normal"> . </span>                <span class="subxComment"># copy *(ebp+8) to esi</span>
<span id="L22" class="LineNr"> 22 </span>    <span class="subxComment"># ecx = s-&gt;read</span>
<span id="L23" class="LineNr"> 23 </span>    8b/copy                         1/mod/*+disp8   6/rm32/esi   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          1/r32/ecx   4/disp8        <span class="Normal"> . </span>                <span class="subxComment"># copy *(esi+4) to ecx</span>
<span id="L24" class="LineNr"> 24 </span>    <span class="subxComment"># if (f-&gt;read &gt;= f-&gt;write) abort</span>
<span id="L25" class="LineNr"> 25 </span>    3b/compare                      0/mod/indirect  6/rm32/esi   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          1/r32/ecx  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># compare ecx with *esi</span>
<span id="L26" class="LineNr"> 26 </span>    0f 8d/jump-if-&gt;=  $read-byte:<a href='317abort.subx.html#L5'>abort</a>/disp32
<span id="L27" class="LineNr"> 27 </span>    <span class="subxComment"># result = f-&gt;data[f-&gt;read]</span>
<span id="L28" class="LineNr"> 28 </span>    31/xor                          3/mod/direct    0/rm32/eax   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          0/r32/eax  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># clear eax</span>
<span id="L29" class="LineNr"> 29 </span>    8a/copy-byte                    1/mod/*+disp8   4/rm32/sib    6/base/esi  1/index/ecx  <span class="Normal"> . </span>          0/r32/AL    0xc/disp8      <span class="Normal"> . </span>                <span class="subxComment"># copy byte at *(esi+ecx+12) to AL</span>
<span id="L30" class="LineNr"> 30 </span>    <span class="subxComment"># ++f-&gt;read</span>
<span id="L31" class="LineNr"> 31 </span>    ff          0/subop/increment   1/mod/*+disp8   6/rm32/esi   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>         <span class="Normal"> . </span>          4/disp8        <span class="Normal"> . </span>                <span class="subxComment"># increment *(esi+4)</span>
<span id="L32" class="LineNr"> 32 </span><span class="Constant">$read-byte:end</span>:
<span id="L33" class="LineNr"> 33 </span>    <span class="subxS1Comment"># . restore registers</span>
<span id="L34" class="LineNr"> 34 </span>    5e/pop-to-esi
<span id="L35" class="LineNr"> 35 </span>    59/pop-to-ecx
<span id="L36" class="LineNr"> 36 </span>    <span class="subxS1Comment"># . epilogue</span>
<span id="L37" class="LineNr"> 37 </span>    89/copy                         3/mod/direct    4/rm32/esp   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          5/r32/ebp  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># copy ebp to esp</span>
<span id="L38" class="LineNr"> 38 </span>    5d/pop-to-ebp
<span id="L39" class="LineNr"> 39 </span>    c3/return
<span id="L40" class="LineNr"> 40 </span>
<span id="L41" class="LineNr"> 41 </span><span class="Constant">$read-byte:<a href='317abort.subx.html#L5'>abort</a></span>:
<span id="L42" class="LineNr"> 42 </span>    (<a href='317abort.subx.html#L5'>abort</a> <span class="Constant">&quot;read-byte: empty stream&quot;</span>)
<span id="L43" class="LineNr"> 43 </span>    <span class="subxComment"># never gets here</span>
<span id="L44" class="LineNr"> 44 </span>
<span id="L45" class="LineNr"> 45 </span>== data
<span id="L46" class="LineNr"> 46 </span>
<span id="L47" class="LineNr"> 47 </span><span class="subxMinorFunction">_test-input-stream</span>:  <span class="subxComment"># (stream byte)</span>
<span id="L48" class="LineNr"> 48 </span>    <span class="subxComment"># current write index</span>
<span id="L49" class="LineNr"> 49 </span>    0/imm32
<span id="L50" class="LineNr"> 50 </span>    <span class="subxComment"># current read index</span>
<span id="L51" class="LineNr"> 51 </span>    0/imm32
<span id="L52" class="LineNr"> 52 </span>    <span class="subxComment"># size</span>
<span id="L53" class="LineNr"> 53 </span>    0x400/imm32  <span class="subxComment"># 1024 bytes</span>
<span id="L54" class="LineNr"> 54 </span>    <span class="subxComment"># data (64 lines x 16 bytes/line)</span>
<span id="L55" class="LineNr"> 55 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L56" class="LineNr"> 56 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L57" class="LineNr"> 57 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L58" class="LineNr"> 58 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L59" class="LineNr"> 59 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L60" class="LineNr"> 60 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L61" class="LineNr"> 61 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L62" class="LineNr"> 62 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L63" class="LineNr"> 63 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L64" class="LineNr"> 64 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L65" class="LineNr"> 65 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L66" class="LineNr"> 66 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L67" class="LineNr"> 67 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L68" class="LineNr"> 68 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L69" class="LineNr"> 69 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L70" class="LineNr"> 70 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L71" class="LineNr"> 71 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L72" class="LineNr"> 72 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L73" class="LineNr"> 73 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L74" class="LineNr"> 74 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L75" class="LineNr"> 75 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L76" class="LineNr"> 76 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L77" class="LineNr"> 77 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L78" class="LineNr"> 78 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L79" class="LineNr"> 79 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L80" class="LineNr"> 80 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L81" class="LineNr"> 81 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L82" class="LineNr"> 82 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L83" class="LineNr"> 83 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L84" class="LineNr"> 84 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L85" class="LineNr"> 85 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L86" class="LineNr"> 86 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L87" class="LineNr"> 87 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L88" class="LineNr"> 88 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L89" class="LineNr"> 89 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L90" class="LineNr"> 90 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L91" class="LineNr"> 91 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L92" class="LineNr"> 92 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L93" class="LineNr"> 93 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L94" class="LineNr"> 94 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L95" class="LineNr"> 95 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L96" class="LineNr"> 96 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L97" class="LineNr"> 97 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L98" class="LineNr"> 98 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L99" class="LineNr"> 99 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L100" class="LineNr">100 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L101" class="LineNr">101 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L102" class="LineNr">102 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L103" class="LineNr">103 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L104" class="LineNr">104 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L105" class="LineNr">105 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L106" class="LineNr">106 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L107" class="LineNr">107 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L108" class="LineNr">108 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L109" class="LineNr">109 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L110" class="LineNr">110 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L111" class="LineNr">111 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L112" class="LineNr">112 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L113" class="LineNr">113 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L114" class="LineNr">114 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L115" class="LineNr">115 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L116" class="LineNr">116 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L117" class="LineNr">117 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L118" class="LineNr">118 </span>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L119" class="LineNr">119 </span>
<span id="L120" class="LineNr">120 </span><span class="subxS2Comment"># . . vim&#0058;nowrap:textwidth=0</span>
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