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<h4 class="subsection">9.22.2 M32R Directives</h4>
<p><a name="index-directives_002c-M32R-1317"></a><a name="index-M32R-directives-1318"></a>
The Renease M32R version of <code>as</code> has a few architecture
specific directives:
<a name="index-g_t_0040code_007blow_007d-directive_002c-M32R-1319"></a>
<dl><dt><code>low </code><var>expression</var><dd>The <code>low</code> directive computes the value of its expression and
places the lower 16-bits of the result into the immediate-field of the
instruction. For example:
<pre class="smallexample"> or3 r0, r0, #low(0x12345678) ; compute r0 = r0 | 0x5678
add3, r0, r0, #low(fred) ; compute r0 = r0 + low 16-bits of address of fred
</pre>
<br><dt><code>high </code><var>expression</var><dd><a name="index-g_t_0040code_007bhigh_007d-directive_002c-M32R-1320"></a>The <code>high</code> directive computes the value of its expression and
places the upper 16-bits of the result into the immediate-field of the
instruction. For example:
<pre class="smallexample"> seth r0, #high(0x12345678) ; compute r0 = 0x12340000
seth, r0, #high(fred) ; compute r0 = upper 16-bits of address of fred
</pre>
<br><dt><code>shigh </code><var>expression</var><dd><a name="index-g_t_0040code_007bshigh_007d-directive_002c-M32R-1321"></a>The <code>shigh</code> directive is very similar to the <code>high</code>
directive. It also computes the value of its expression and places
the upper 16-bits of the result into the immediate-field of the
instruction. The difference is that <code>shigh</code> also checks to see
if the lower 16-bits could be interpreted as a signed number, and if
so it assumes that a borrow will occur from the upper-16 bits. To
compensate for this the <code>shigh</code> directive pre-biases the upper
16 bit value by adding one to it. For example:
<p>For example:
<pre class="smallexample"> seth r0, #shigh(0x12345678) ; compute r0 = 0x12340000
seth r0, #shigh(0x00008000) ; compute r0 = 0x00010000
</pre>
<p>In the second example the lower 16-bits are 0x8000. If these are
treated as a signed value and sign extended to 32-bits then the value
becomes 0xffff8000. If this value is then added to 0x00010000 then
the result is 0x00008000.
<p>This behaviour is to allow for the different semantics of the
<code>or3</code> and <code>add3</code> instructions. The <code>or3</code> instruction
treats its 16-bit immediate argument as unsigned whereas the
<code>add3</code> treats its 16-bit immediate as a signed value. So for
example:
<pre class="smallexample"> seth r0, #shigh(0x00008000)
add3 r0, r0, #low(0x00008000)
</pre>
<p>Produces the correct result in r0, whereas:
<pre class="smallexample"> seth r0, #shigh(0x00008000)
or3 r0, r0, #low(0x00008000)
</pre>
<p>Stores 0xffff8000 into r0.
<p>Note - the <code>shigh</code> directive does not know where in the assembly
source code the lower 16-bits of the value are going set, so it cannot
check to make sure that an <code>or3</code> instruction is being used rather
than an <code>add3</code> instruction. It is up to the programmer to make
sure that correct directives are used.
<p><a name="index-g_t_0040code_007b_002em32r_007d-directive_002c-M32R-1322"></a><br><dt><code>.m32r</code><dd>The directive performs a similar thing as the <em>-m32r</em> command
line option. It tells the assembler to only accept M32R instructions
from now on. An instructions from later M32R architectures are
refused.
<p><a name="index-g_t_0040code_007b_002em32rx_007d-directive_002c-M32RX-1323"></a><br><dt><code>.m32rx</code><dd>The directive performs a similar thing as the <em>-m32rx</em> command
line option. It tells the assembler to start accepting the extra
instructions in the M32RX ISA as well as the ordinary M32R ISA.
<p><a name="index-g_t_0040code_007b_002em32r2_007d-directive_002c-M32R2-1324"></a><br><dt><code>.m32r2</code><dd>The directive performs a similar thing as the <em>-m32r2</em> command
line option. It tells the assembler to start accepting the extra
instructions in the M32R2 ISA as well as the ordinary M32R ISA.
<p><a name="index-g_t_0040code_007b_002elittle_007d-directive_002c-M32RX-1325"></a><br><dt><code>.little</code><dd>The directive performs a similar thing as the <em>-little</em> command
line option. It tells the assembler to start producing little-endian
code and data. This option should be used with care as producing
mixed-endian binary files is fraught with danger.
<p><a name="index-g_t_0040code_007b_002ebig_007d-directive_002c-M32RX-1326"></a><br><dt><code>.big</code><dd>The directive performs a similar thing as the <em>-big</em> command
line option. It tells the assembler to start producing big-endian
code and data. This option should be used with care as producing
mixed-endian binary files is fraught with danger.
</dl>
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