324 lines
14 KiB
HTML
324 lines
14 KiB
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- This file documents the GNU Assembler "as".
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Copyright (C) 1991-2016 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Using as: MMIX-Pseudos</title>
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<meta name="description" content="Using as: MMIX-Pseudos">
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<meta name="keywords" content="Using as: MMIX-Pseudos">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="AS-Index.html#AS-Index" rel="index" title="AS Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="MMIX_002dSyntax.html#MMIX_002dSyntax" rel="up" title="MMIX-Syntax">
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<link href="MMIX_002dmmixal.html#MMIX_002dmmixal" rel="next" title="MMIX-mmixal">
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<link href="MMIX_002dRegs.html#MMIX_002dRegs" rel="prev" title="MMIX-Regs">
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</head>
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="MMIX_002dPseudos"></a>
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<div class="header">
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<p>
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Previous: <a href="MMIX_002dRegs.html#MMIX_002dRegs" accesskey="p" rel="prev">MMIX-Regs</a>, Up: <a href="MMIX_002dSyntax.html#MMIX_002dSyntax" accesskey="u" rel="up">MMIX-Syntax</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Assembler-Directives-3"></a>
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<h4 class="subsubsection">9.28.3.4 Assembler Directives</h4>
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<a name="index-assembler-directives_002c-MMIX"></a>
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<a name="index-pseudo_002dops_002c-MMIX"></a>
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<a name="index-MMIX-assembler-directives"></a>
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<a name="index-MMIX-pseudo_002dops"></a>
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<dl compact="compact">
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<dt><code>LOC</code></dt>
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<dd><a name="index-assembler-directive-LOC_002c-MMIX"></a>
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<a name="index-pseudo_002dop-LOC_002c-MMIX"></a>
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<a name="index-MMIX-assembler-directive-LOC"></a>
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<a name="index-MMIX-pseudo_002dop-LOC"></a>
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<a name="MMIX_002dloc"></a><p>The <code>LOC</code> directive sets the current location to the value of the
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operand field, which may include changing sections. If the operand is a
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constant, the section is set to either <code>.data</code> if the value is
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<code>0x2000000000000000</code> or larger, else it is set to <code>.text</code>.
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Within a section, the current location may only be changed to
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monotonically higher addresses. A LOC expression must be a previously
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defined symbol or a “pure” constant.
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</p>
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<p>An example, which sets the label <var>prev</var> to the current location, and
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updates the current location to eight bytes forward:
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</p><div class="smallexample">
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<pre class="smallexample">prev LOC @+8
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</pre></div>
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<p>When a LOC has a constant as its operand, a symbol
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<code>__.MMIX.start..text</code> or <code>__.MMIX.start..data</code> is defined
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depending on the address as mentioned above. Each such symbol is
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interpreted as special by the linker, locating the section at that
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address. Note that if multiple files are linked, the first object file
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with that section will be mapped to that address (not necessarily the file
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with the LOC definition).
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</p>
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</dd>
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<dt><code>LOCAL</code></dt>
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<dd><a name="index-assembler-directive-LOCAL_002c-MMIX"></a>
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<a name="index-pseudo_002dop-LOCAL_002c-MMIX"></a>
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<a name="index-MMIX-assembler-directive-LOCAL"></a>
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<a name="index-MMIX-pseudo_002dop-LOCAL"></a>
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<a name="MMIX_002dlocal"></a><p>Example:
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</p><div class="smallexample">
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<pre class="smallexample"> LOCAL external_symbol
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LOCAL 42
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.local asymbol
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</pre></div>
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<p>This directive-operation generates a link-time assertion that the operand
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does not correspond to a global register. The operand is an expression
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that at link-time resolves to a register symbol or a number. A number is
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treated as the register having that number. There is one restriction on
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the use of this directive: the pseudo-directive must be placed in a
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section with contents, code or data.
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</p>
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</dd>
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<dt><code>IS</code></dt>
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<dd><a name="index-assembler-directive-IS_002c-MMIX"></a>
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<a name="index-pseudo_002dop-IS_002c-MMIX"></a>
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<a name="index-MMIX-assembler-directive-IS"></a>
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<a name="index-MMIX-pseudo_002dop-IS"></a>
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<a name="MMIX_002dis"></a><p>The <code>IS</code> directive:
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</p><div class="smallexample">
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<pre class="smallexample">asymbol IS an_expression
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</pre></div>
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<p>sets the symbol ‘<samp>asymbol</samp>’ to ‘<samp>an_expression</samp>’. A symbol may not
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be set more than once using this directive. Local labels may be set using
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this directive, for example:
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</p><div class="smallexample">
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<pre class="smallexample">5H IS @+4
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</pre></div>
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</dd>
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<dt><code>GREG</code></dt>
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<dd><a name="index-assembler-directive-GREG_002c-MMIX"></a>
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<a name="index-pseudo_002dop-GREG_002c-MMIX"></a>
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<a name="index-MMIX-assembler-directive-GREG"></a>
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<a name="index-MMIX-pseudo_002dop-GREG"></a>
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<a name="MMIX_002dgreg"></a><p>This directive reserves a global register, gives it an initial value and
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optionally gives it a symbolic name. Some examples:
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</p>
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<div class="smallexample">
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<pre class="smallexample">areg GREG
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breg GREG data_value
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GREG data_buffer
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.greg creg, another_data_value
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</pre></div>
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<p>The symbolic register name can be used in place of a (non-special)
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register. If a value isn’t provided, it defaults to zero. Unless the
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option ‘<samp>--no-merge-gregs</samp>’ is specified, non-zero registers allocated
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with this directive may be eliminated by <code>as</code>; another
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register with the same value used in its place.
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Any of the instructions
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‘<samp>CSWAP</samp>’,
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‘<samp>GO</samp>’,
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‘<samp>LDA</samp>’,
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‘<samp>LDBU</samp>’,
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‘<samp>LDB</samp>’,
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‘<samp>LDHT</samp>’,
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‘<samp>LDOU</samp>’,
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‘<samp>LDO</samp>’,
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‘<samp>LDSF</samp>’,
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‘<samp>LDTU</samp>’,
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‘<samp>LDT</samp>’,
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‘<samp>LDUNC</samp>’,
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‘<samp>LDVTS</samp>’,
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‘<samp>LDWU</samp>’,
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‘<samp>LDW</samp>’,
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‘<samp>PREGO</samp>’,
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‘<samp>PRELD</samp>’,
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‘<samp>PREST</samp>’,
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‘<samp>PUSHGO</samp>’,
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‘<samp>STBU</samp>’,
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‘<samp>STB</samp>’,
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‘<samp>STCO</samp>’,
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‘<samp>STHT</samp>’,
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‘<samp>STOU</samp>’,
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‘<samp>STSF</samp>’,
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‘<samp>STTU</samp>’,
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‘<samp>STT</samp>’,
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‘<samp>STUNC</samp>’,
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‘<samp>SYNCD</samp>’,
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‘<samp>SYNCID</samp>’,
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can have a value nearby <a name="GREG_002dbase"></a>an initial value in place of its
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second and third operands. Here, “nearby” is defined as within the
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range 0…255 from the initial value of such an allocated register.
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</p>
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<div class="smallexample">
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<pre class="smallexample">buffer1 BYTE 0,0,0,0,0
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buffer2 BYTE 0,0,0,0,0
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…
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GREG buffer1
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LDOU $42,buffer2
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</pre></div>
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<p>In the example above, the ‘<samp>Y</samp>’ field of the <code>LDOUI</code> instruction
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(LDOU with a constant Z) will be replaced with the global register
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allocated for ‘<samp>buffer1</samp>’, and the ‘<samp>Z</samp>’ field will have the value
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5, the offset from ‘<samp>buffer1</samp>’ to ‘<samp>buffer2</samp>’. The result is
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equivalent to this code:
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</p><div class="smallexample">
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<pre class="smallexample">buffer1 BYTE 0,0,0,0,0
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buffer2 BYTE 0,0,0,0,0
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…
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tmpreg GREG buffer1
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LDOU $42,tmpreg,(buffer2-buffer1)
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</pre></div>
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<p>Global registers allocated with this directive are allocated in order
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higher-to-lower within a file. Other than that, the exact order of
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register allocation and elimination is undefined. For example, the order
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is undefined when more than one file with such directives are linked
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together. With the options ‘<samp>-x</samp>’ and ‘<samp>--linker-allocated-gregs</samp>’,
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‘<samp>GREG</samp>’ directives for two-operand cases like the one mentioned above
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can be omitted. Sufficient global registers will then be allocated by the
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linker.
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</p>
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</dd>
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<dt><code>BYTE</code></dt>
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<dd><a name="index-assembler-directive-BYTE_002c-MMIX"></a>
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<a name="index-pseudo_002dop-BYTE_002c-MMIX"></a>
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<a name="index-MMIX-assembler-directive-BYTE"></a>
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<a name="index-MMIX-pseudo_002dop-BYTE"></a>
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<a name="MMIX_002dbyte"></a><p>The ‘<samp>BYTE</samp>’ directive takes a series of operands separated by a comma.
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If an operand is a string (see <a href="Strings.html#Strings">Strings</a>), each character of that string
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is emitted as a byte. Other operands must be constant expressions without
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forward references, in the range 0…255. If you need operands having
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expressions with forward references, use ‘<samp>.byte</samp>’ (see <a href="Byte.html#Byte">Byte</a>). An
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operand can be omitted, defaulting to a zero value.
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</p>
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</dd>
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<dt><code>WYDE</code></dt>
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<dt><code>TETRA</code></dt>
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<dt><code>OCTA</code></dt>
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<dd><a name="index-assembler-directive-WYDE_002c-MMIX"></a>
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<a name="index-pseudo_002dop-WYDE_002c-MMIX"></a>
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<a name="index-MMIX-assembler-directive-WYDE"></a>
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<a name="index-MMIX-pseudo_002dop-WYDE"></a>
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<a name="index-assembler-directive-TETRA_002c-MMIX"></a>
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<a name="index-pseudo_002dop-TETRA_002c-MMIX"></a>
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<a name="index-MMIX-assembler-directive-TETRA"></a>
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<a name="index-MMIX-pseudo_002dop-TETRA"></a>
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<a name="index-assembler-directive-OCTA_002c-MMIX"></a>
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<a name="index-pseudo_002dop-OCTA_002c-MMIX"></a>
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<a name="index-MMIX-assembler-directive-OCTA"></a>
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<a name="index-MMIX-pseudo_002dop-OCTA"></a>
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<a name="MMIX_002dconstants"></a><p>The directives ‘<samp>WYDE</samp>’, ‘<samp>TETRA</samp>’ and ‘<samp>OCTA</samp>’ emit constants of
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two, four and eight bytes size respectively. Before anything else happens
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for the directive, the current location is aligned to the respective
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constant-size boundary. If a label is defined at the beginning of the
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line, its value will be that after the alignment. A single operand can be
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omitted, defaulting to a zero value emitted for the directive. Operands
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can be expressed as strings (see <a href="Strings.html#Strings">Strings</a>), in which case each
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character in the string is emitted as a separate constant of the size
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indicated by the directive.
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</p>
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</dd>
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<dt><code>PREFIX</code></dt>
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<dd><a name="index-assembler-directive-PREFIX_002c-MMIX"></a>
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<a name="index-pseudo_002dop-PREFIX_002c-MMIX"></a>
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<a name="index-MMIX-assembler-directive-PREFIX"></a>
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<a name="index-MMIX-pseudo_002dop-PREFIX"></a>
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<a name="MMIX_002dprefix"></a><p>The ‘<samp>PREFIX</samp>’ directive sets a symbol name prefix to be prepended to
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all symbols (except local symbols, see <a href="MMIX_002dSymbols.html#MMIX_002dSymbols">MMIX-Symbols</a>), that are not
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prefixed with ‘<samp>:</samp>’, until the next ‘<samp>PREFIX</samp>’ directive. Such
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prefixes accumulate. For example,
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</p><div class="smallexample">
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<pre class="smallexample"> PREFIX a
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PREFIX b
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c IS 0
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</pre></div>
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<p>defines a symbol ‘<samp>abc</samp>’ with the value 0.
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</p>
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</dd>
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<dt><code>BSPEC</code></dt>
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<dt><code>ESPEC</code></dt>
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<dd><a name="index-assembler-directive-BSPEC_002c-MMIX"></a>
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<a name="index-pseudo_002dop-BSPEC_002c-MMIX"></a>
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<a name="index-MMIX-assembler-directive-BSPEC"></a>
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<a name="index-MMIX-pseudo_002dop-BSPEC"></a>
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<a name="index-assembler-directive-ESPEC_002c-MMIX"></a>
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<a name="index-pseudo_002dop-ESPEC_002c-MMIX"></a>
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<a name="index-MMIX-assembler-directive-ESPEC"></a>
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<a name="index-MMIX-pseudo_002dop-ESPEC"></a>
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<a name="MMIX_002dspec"></a><p>A pair of ‘<samp>BSPEC</samp>’ and ‘<samp>ESPEC</samp>’ directives delimit a section of
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special contents (without specified semantics). Example:
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</p><div class="smallexample">
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<pre class="smallexample"> BSPEC 42
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TETRA 1,2,3
|
||
|
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ESPEC
|
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</pre></div>
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<p>The single operand to ‘<samp>BSPEC</samp>’ must be number in the range
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0…255. The ‘<samp>BSPEC</samp>’ number 80 is used by the GNU binutils
|
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implementation.
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</p></dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Previous: <a href="MMIX_002dRegs.html#MMIX_002dRegs" accesskey="p" rel="prev">MMIX-Regs</a>, Up: <a href="MMIX_002dSyntax.html#MMIX_002dSyntax" accesskey="u" rel="up">MMIX-Syntax</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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