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<title>Using as: M32R-Directives</title>
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<a name="M32R_002dDirectives"></a>
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<p>
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Next: <a href="M32R_002dWarnings.html#M32R_002dWarnings" accesskey="n" rel="next">M32R-Warnings</a>, Previous: <a href="M32R_002dOpts.html#M32R_002dOpts" accesskey="p" rel="prev">M32R-Opts</a>, Up: <a href="M32R_002dDependent.html#M32R_002dDependent" accesskey="u" rel="up">M32R-Dependent</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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<hr>
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<a name="M32R-Directives"></a>
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<h4 class="subsection">9.22.2 M32R Directives</h4>
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<a name="index-directives_002c-M32R"></a>
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<a name="index-M32R-directives"></a>
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<p>The Renease M32R version of <code>as</code> has a few architecture
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specific directives:
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</p>
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<dl compact="compact">
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<dd>
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<a name="index-low-directive_002c-M32R"></a>
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</dd>
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<dt><code>low <var>expression</var></code></dt>
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<dd><p>The <code>low</code> directive computes the value of its expression and
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places the lower 16-bits of the result into the immediate-field of the
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instruction. For example:
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</p>
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<div class="smallexample">
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<pre class="smallexample"> or3 r0, r0, #low(0x12345678) ; compute r0 = r0 | 0x5678
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add3, r0, r0, #low(fred) ; compute r0 = r0 + low 16-bits of address of fred
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</pre></div>
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</dd>
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<dt><code>high <var>expression</var></code></dt>
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<dd><a name="index-high-directive_002c-M32R"></a>
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<p>The <code>high</code> directive computes the value of its expression and
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places the upper 16-bits of the result into the immediate-field of the
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instruction. For example:
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</p>
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<div class="smallexample">
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<pre class="smallexample"> seth r0, #high(0x12345678) ; compute r0 = 0x12340000
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seth, r0, #high(fred) ; compute r0 = upper 16-bits of address of fred
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</pre></div>
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</dd>
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<dt><code>shigh <var>expression</var></code></dt>
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<dd><a name="index-shigh-directive_002c-M32R"></a>
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<p>The <code>shigh</code> directive is very similar to the <code>high</code>
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directive. It also computes the value of its expression and places
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the upper 16-bits of the result into the immediate-field of the
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instruction. The difference is that <code>shigh</code> also checks to see
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if the lower 16-bits could be interpreted as a signed number, and if
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so it assumes that a borrow will occur from the upper-16 bits. To
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compensate for this the <code>shigh</code> directive pre-biases the upper
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16 bit value by adding one to it. For example:
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</p>
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<p>For example:
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</p>
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<div class="smallexample">
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<pre class="smallexample"> seth r0, #shigh(0x12345678) ; compute r0 = 0x12340000
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seth r0, #shigh(0x00008000) ; compute r0 = 0x00010000
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</pre></div>
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<p>In the second example the lower 16-bits are 0x8000. If these are
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treated as a signed value and sign extended to 32-bits then the value
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becomes 0xffff8000. If this value is then added to 0x00010000 then
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the result is 0x00008000.
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</p>
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<p>This behaviour is to allow for the different semantics of the
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<code>or3</code> and <code>add3</code> instructions. The <code>or3</code> instruction
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treats its 16-bit immediate argument as unsigned whereas the
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<code>add3</code> treats its 16-bit immediate as a signed value. So for
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example:
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</p>
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<div class="smallexample">
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<pre class="smallexample"> seth r0, #shigh(0x00008000)
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add3 r0, r0, #low(0x00008000)
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</pre></div>
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<p>Produces the correct result in r0, whereas:
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</p>
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<div class="smallexample">
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<pre class="smallexample"> seth r0, #shigh(0x00008000)
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or3 r0, r0, #low(0x00008000)
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</pre></div>
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<p>Stores 0xffff8000 into r0.
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</p>
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<p>Note - the <code>shigh</code> directive does not know where in the assembly
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source code the lower 16-bits of the value are going set, so it cannot
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check to make sure that an <code>or3</code> instruction is being used rather
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than an <code>add3</code> instruction. It is up to the programmer to make
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sure that correct directives are used.
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</p>
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<a name="index-_002em32r-directive_002c-M32R"></a>
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</dd>
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<dt><code>.m32r</code></dt>
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<dd><p>The directive performs a similar thing as the <em>-m32r</em> command
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line option. It tells the assembler to only accept M32R instructions
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from now on. An instructions from later M32R architectures are
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refused.
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</p>
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<a name="index-_002em32rx-directive_002c-M32RX"></a>
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</dd>
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<dt><code>.m32rx</code></dt>
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<dd><p>The directive performs a similar thing as the <em>-m32rx</em> command
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line option. It tells the assembler to start accepting the extra
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instructions in the M32RX ISA as well as the ordinary M32R ISA.
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</p>
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<a name="index-_002em32r2-directive_002c-M32R2"></a>
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</dd>
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<dt><code>.m32r2</code></dt>
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<dd><p>The directive performs a similar thing as the <em>-m32r2</em> command
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line option. It tells the assembler to start accepting the extra
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instructions in the M32R2 ISA as well as the ordinary M32R ISA.
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</p>
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<a name="index-_002elittle-directive_002c-M32RX"></a>
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</dd>
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<dt><code>.little</code></dt>
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<dd><p>The directive performs a similar thing as the <em>-little</em> command
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line option. It tells the assembler to start producing little-endian
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code and data. This option should be used with care as producing
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mixed-endian binary files is fraught with danger.
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</p>
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<a name="index-_002ebig-directive_002c-M32RX"></a>
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</dd>
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<dt><code>.big</code></dt>
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<dd><p>The directive performs a similar thing as the <em>-big</em> command
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line option. It tells the assembler to start producing big-endian
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code and data. This option should be used with care as producing
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mixed-endian binary files is fraught with danger.
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</p>
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</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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Next: <a href="M32R_002dWarnings.html#M32R_002dWarnings" accesskey="n" rel="next">M32R-Warnings</a>, Previous: <a href="M32R_002dOpts.html#M32R_002dOpts" accesskey="p" rel="prev">M32R-Opts</a>, Up: <a href="M32R_002dDependent.html#M32R_002dDependent" accesskey="u" rel="up">M32R-Dependent</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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