2021-01-21 13:40:28 +01:00
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</head><body>
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<p><span class="h1">Working With Assembly Language</span>
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<br/><br/>
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RETRO runs on a virtual machine called Nga. It provides a
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standard assembler for this called <strong>Muri</strong>.
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<br/><br/>
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Muri is a simple, multipass model that's not fancy, but
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suffices for RETRO's needs.
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<br/><br/>
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<span class="h2">Assembling A Standalone File</span>
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<br/><br/>
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A small example (<strong>test.muri</strong>)
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<br/><br/>
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<tt class='indentedcode'>~~~</tt>
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<tt class='indentedcode'>i liju....</tt>
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<tt class='indentedcode'>r main</tt>
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<tt class='indentedcode'>: c:put</tt>
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<tt class='indentedcode'>i liiire..</tt>
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<tt class='indentedcode'>i 0</tt>
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<tt class='indentedcode'>: main</tt>
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<tt class='indentedcode'>i lilica..</tt>
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<tt class='indentedcode'>d 97</tt>
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<tt class='indentedcode'>i liju....</tt>
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<tt class='indentedcode'>r main</tt>
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<tt class='indentedcode'>~~~</tt>
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<br/><br/>
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Assembling it:
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<br/><br/>
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<tt class='indentedcode'>retro-muri test.muri</tt>
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<br/><br/>
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So breaking down: Muri extracts the assembly code blocks to
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assemble, then proceeds to do the assembly. Each source line
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starts with a directive, followed by a space, and then ending
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with a value.
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<br/><br/>
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The directives are:
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<br/><br/>
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<tt class='indentedcode'>: value is a label</tt>
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<tt class='indentedcode'>i value is an instruction bundle</tt>
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<tt class='indentedcode'>d value is a numeric value</tt>
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<tt class='indentedcode'>r value is a reference</tt>
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<tt class='indentedcode'>s value is a string to inline</tt>
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<br/><br/>
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Instructions for Nga are provided as bundles. Each memory
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location can store up to four instructions. And each instruction
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gets a two character identifier.
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<br/><br/>
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From the list of instructions:
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<br/><br/>
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<tt class='indentedcode'>0 nop 5 push 10 ret 15 fetch 20 div 25 zret</tt>
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<tt class='indentedcode'>1 lit 6 pop 11 eq 16 store 21 and 26 halt</tt>
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<tt class='indentedcode'>2 dup 7 jump 12 neq 17 add 22 or 27 ienum</tt>
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<tt class='indentedcode'>3 drop 8 call 13 lt 18 sub 23 xor 28 iquery</tt>
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<tt class='indentedcode'>4 swap 9 ccall 14 gt 19 mul 24 shift 29 iinvoke</tt>
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<br/><br/>
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This reduces to:
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<br/><br/>
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<tt class='indentedcode'>0 .. 5 pu 10 re 15 fe 20 di 25 zr</tt>
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<tt class='indentedcode'>1 li 6 po 11 eq 16 st 21 an 26 ha</tt>
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<tt class='indentedcode'>2 du 7 ju 12 ne 17 ad 22 or 27 ie</tt>
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<tt class='indentedcode'>3 dr 8 ca 13 lt 18 su 23 xo 28 iq</tt>
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<tt class='indentedcode'>4 sw 9 cc 14 gt 19 mu 24 sh 29 ii</tt>
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<br/><br/>
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Most are just the first two letters of the instruction name. I
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use <span class="tt">..</span> instead of <span class="tt">no</span> for <span class="tt">NOP</span>, and the first letter of
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each I/O instruction name. So a bundle may look like:
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<br/><br/>
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<tt class='indentedcode'>dumure..</tt>
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<br/><br/>
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(This would correspond to <span class="tt">dup multiply return nop</span>).
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<br/><br/>
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<span class="h2">Runtime Assembler</span>
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<br/><br/>
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RETRO also has a runtime variation of Muri that can be used
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when you need to generate more optimal code. So one can write:
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<br/><br/>
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<tt class='indentedcode'>:n:square dup * ;</tt>
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<br/><br/>
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Or:
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<br/><br/>
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<tt class='indentedcode'>:n:square \dumure.. ;</tt>
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<br/><br/>
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The second one will be faster, as the entire definition is one
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bundle, which reduces memory reads and decoding by 2/3.
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<br/><br/>
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Doing this is less readable, so I only recommend doing so after
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you have finalized working RETRO level code and determined the
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best places to optimize.
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<br/><br/>
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The runtime assembler has the following directives:
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<br/><br/>
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<tt class='indentedcode'>i value is an instruction bundle</tt>
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<tt class='indentedcode'>d value is a numeric value</tt>
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<tt class='indentedcode'>r value is a reference</tt>
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<br/><br/>
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Additionally, in the runtime assembler, these are reversed:
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<br/><br/>
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<tt class='indentedcode'>'dudumu.. i</tt>
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<br/><br/>
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Instead of:
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<br/><br/>
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<tt class='indentedcode'>i dudumu..</tt>
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<br/><br/>
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2021-03-30 13:58:25 +02:00
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The runtime assembler also provides three sigils for use in
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2021-01-21 13:40:28 +01:00
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inlining machine code into a definition. These are:
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<br/><br/>
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<tt class='indentedcode'> \ Treat token as an assembly sequence</tt>
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<tt class='indentedcode'> ` Treat token as a numeric value</tt>
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<tt class='indentedcode'> ^ Treat token as a reference</tt>
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<br/><br/>
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E.g., instead of doing something like:
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<br/><br/>
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<tt class='indentedcode'>:n:square as{ 'dumu.... i }as ;</tt>
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<tt class='indentedcode'>:test as{ 'lilica.... i #22 d 'n:square r }as ;</tt>
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<br/><br/>
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Just write:
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<tt class='indentedcode'>:n:square \dumu.... ;</tt>
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<tt class='indentedcode'>:test \lilica.. `22 ^n:square ; </tt>
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</p>
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</body></html>
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