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| <a name="Conversions-1"></a> |
| <h3 class="section">13.13 Conversions</h3> |
| <a name="index-conversions"></a> |
| <a name="index-machine-mode-conversions"></a> |
| |
| <p>All conversions between machine modes must be represented by |
| explicit conversion operations. For example, an expression |
| which is the sum of a byte and a full word cannot be written as |
| <code>(plus:SI (reg:QI 34) (reg:SI 80))</code> because the <code>plus</code> |
| operation requires two operands of the same machine mode. |
| Therefore, the byte-sized operand is enclosed in a conversion |
| operation, as in |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(plus:SI (sign_extend:SI (reg:QI 34)) (reg:SI 80)) |
| </pre></div> |
| |
| <p>The conversion operation is not a mere placeholder, because there |
| may be more than one way of converting from a given starting mode |
| to the desired final mode. The conversion operation code says how |
| to do it. |
| </p> |
| <p>For all conversion operations, <var>x</var> must not be <code>VOIDmode</code> |
| because the mode in which to do the conversion would not be known. |
| The conversion must either be done at compile-time or <var>x</var> |
| must be placed into a register. |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-sign_005fextend"></a> |
| </dd> |
| <dt><code>(sign_extend:<var>m</var> <var>x</var>)</code></dt> |
| <dd><p>Represents the result of sign-extending the value <var>x</var> |
| to machine mode <var>m</var>. <var>m</var> must be a fixed-point mode |
| and <var>x</var> a fixed-point value of a mode narrower than <var>m</var>. |
| </p> |
| <a name="index-zero_005fextend"></a> |
| </dd> |
| <dt><code>(zero_extend:<var>m</var> <var>x</var>)</code></dt> |
| <dd><p>Represents the result of zero-extending the value <var>x</var> |
| to machine mode <var>m</var>. <var>m</var> must be a fixed-point mode |
| and <var>x</var> a fixed-point value of a mode narrower than <var>m</var>. |
| </p> |
| <a name="index-float_005fextend"></a> |
| </dd> |
| <dt><code>(float_extend:<var>m</var> <var>x</var>)</code></dt> |
| <dd><p>Represents the result of extending the value <var>x</var> |
| to machine mode <var>m</var>. <var>m</var> must be a floating point mode |
| and <var>x</var> a floating point value of a mode narrower than <var>m</var>. |
| </p> |
| <a name="index-truncate"></a> |
| </dd> |
| <dt><code>(truncate:<var>m</var> <var>x</var>)</code></dt> |
| <dd><p>Represents the result of truncating the value <var>x</var> |
| to machine mode <var>m</var>. <var>m</var> must be a fixed-point mode |
| and <var>x</var> a fixed-point value of a mode wider than <var>m</var>. |
| </p> |
| <a name="index-ss_005ftruncate"></a> |
| </dd> |
| <dt><code>(ss_truncate:<var>m</var> <var>x</var>)</code></dt> |
| <dd><p>Represents the result of truncating the value <var>x</var> |
| to machine mode <var>m</var>, using signed saturation in the case of |
| overflow. Both <var>m</var> and the mode of <var>x</var> must be fixed-point |
| modes. |
| </p> |
| <a name="index-us_005ftruncate"></a> |
| </dd> |
| <dt><code>(us_truncate:<var>m</var> <var>x</var>)</code></dt> |
| <dd><p>Represents the result of truncating the value <var>x</var> |
| to machine mode <var>m</var>, using unsigned saturation in the case of |
| overflow. Both <var>m</var> and the mode of <var>x</var> must be fixed-point |
| modes. |
| </p> |
| <a name="index-float_005ftruncate"></a> |
| </dd> |
| <dt><code>(float_truncate:<var>m</var> <var>x</var>)</code></dt> |
| <dd><p>Represents the result of truncating the value <var>x</var> |
| to machine mode <var>m</var>. <var>m</var> must be a floating point mode |
| and <var>x</var> a floating point value of a mode wider than <var>m</var>. |
| </p> |
| <a name="index-float"></a> |
| </dd> |
| <dt><code>(float:<var>m</var> <var>x</var>)</code></dt> |
| <dd><p>Represents the result of converting fixed point value <var>x</var>, |
| regarded as signed, to floating point mode <var>m</var>. |
| </p> |
| <a name="index-unsigned_005ffloat"></a> |
| </dd> |
| <dt><code>(unsigned_float:<var>m</var> <var>x</var>)</code></dt> |
| <dd><p>Represents the result of converting fixed point value <var>x</var>, |
| regarded as unsigned, to floating point mode <var>m</var>. |
| </p> |
| <a name="index-fix"></a> |
| </dd> |
| <dt><code>(fix:<var>m</var> <var>x</var>)</code></dt> |
| <dd><p>When <var>m</var> is a floating-point mode, represents the result of |
| converting floating point value <var>x</var> (valid for mode <var>m</var>) to an |
| integer, still represented in floating point mode <var>m</var>, by rounding |
| towards zero. |
| </p> |
| <p>When <var>m</var> is a fixed-point mode, represents the result of |
| converting floating point value <var>x</var> to mode <var>m</var>, regarded as |
| signed. How rounding is done is not specified, so this operation may |
| be used validly in compiling C code only for integer-valued operands. |
| </p> |
| <a name="index-unsigned_005ffix"></a> |
| </dd> |
| <dt><code>(unsigned_fix:<var>m</var> <var>x</var>)</code></dt> |
| <dd><p>Represents the result of converting floating point value <var>x</var> to |
| fixed point mode <var>m</var>, regarded as unsigned. How rounding is done |
| is not specified. |
| </p> |
| <a name="index-fract_005fconvert"></a> |
| </dd> |
| <dt><code>(fract_convert:<var>m</var> <var>x</var>)</code></dt> |
| <dd><p>Represents the result of converting fixed-point value <var>x</var> to |
| fixed-point mode <var>m</var>, signed integer value <var>x</var> to |
| fixed-point mode <var>m</var>, floating-point value <var>x</var> to |
| fixed-point mode <var>m</var>, fixed-point value <var>x</var> to integer mode <var>m</var> |
| regarded as signed, or fixed-point value <var>x</var> to floating-point mode <var>m</var>. |
| When overflows or underflows happen, the results are undefined. |
| </p> |
| <a name="index-sat_005ffract"></a> |
| </dd> |
| <dt><code>(sat_fract:<var>m</var> <var>x</var>)</code></dt> |
| <dd><p>Represents the result of converting fixed-point value <var>x</var> to |
| fixed-point mode <var>m</var>, signed integer value <var>x</var> to |
| fixed-point mode <var>m</var>, or floating-point value <var>x</var> to |
| fixed-point mode <var>m</var>. |
| When overflows or underflows happen, the results are saturated to the |
| maximum or the minimum. |
| </p> |
| <a name="index-unsigned_005ffract_005fconvert"></a> |
| </dd> |
| <dt><code>(unsigned_fract_convert:<var>m</var> <var>x</var>)</code></dt> |
| <dd><p>Represents the result of converting fixed-point value <var>x</var> to |
| integer mode <var>m</var> regarded as unsigned, or unsigned integer value <var>x</var> to |
| fixed-point mode <var>m</var>. |
| When overflows or underflows happen, the results are undefined. |
| </p> |
| <a name="index-unsigned_005fsat_005ffract"></a> |
| </dd> |
| <dt><code>(unsigned_sat_fract:<var>m</var> <var>x</var>)</code></dt> |
| <dd><p>Represents the result of converting unsigned integer value <var>x</var> to |
| fixed-point mode <var>m</var>. |
| When overflows or underflows happen, the results are saturated to the |
| maximum or the minimum. |
| </p></dd> |
| </dl> |
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