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<h3 class="section">13.11 Bit-Fields</h3>
<p><a name="index-bit_002dfields-3001"></a>
Special expression codes exist to represent bit-field instructions.
<a name="index-sign_005fextract-3002"></a>
<a name="index-g_t_0040code_007bBITS_005fBIG_005fENDIAN_007d_002c-effect-on-_0040code_007bsign_005fextract_007d-3003"></a>
<dl><dt><code>(sign_extract:</code><var>m</var> <var>loc</var> <var>size</var> <var>pos</var><code>)</code><dd>This represents a reference to a sign-extended bit-field contained or
starting in <var>loc</var> (a memory or register reference). The bit-field
is <var>size</var> bits wide and starts at bit <var>pos</var>. The compilation
option <code>BITS_BIG_ENDIAN</code> says which end of the memory unit
<var>pos</var> counts from.
<p>If <var>loc</var> is in memory, its mode must be a single-byte integer mode.
If <var>loc</var> is in a register, the mode to use is specified by the
operand of the <code>insv</code> or <code>extv</code> pattern
(see <a href="Standard-Names.html#Standard-Names">Standard Names</a>) and is usually a full-word integer mode,
which is the default if none is specified.
<p>The mode of <var>pos</var> is machine-specific and is also specified
in the <code>insv</code> or <code>extv</code> pattern.
<p>The mode <var>m</var> is the same as the mode that would be used for
<var>loc</var> if it were a register.
<p>A <code>sign_extract</code> can not appear as an lvalue, or part thereof,
in RTL.
<p><a name="index-zero_005fextract-3004"></a><br><dt><code>(zero_extract:</code><var>m</var> <var>loc</var> <var>size</var> <var>pos</var><code>)</code><dd>Like <code>sign_extract</code> but refers to an unsigned or zero-extended
bit-field. The same sequence of bits are extracted, but they
are filled to an entire word with zeros instead of by sign-extension.
<p>Unlike <code>sign_extract</code>, this type of expressions can be lvalues
in RTL; they may appear on the left side of an assignment, indicating
insertion of a value into the specified bit-field.
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