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| <title>GNU Compiler Collection (GCC) Internals: Floating Point</title> |
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| <a name="Cross-Compilation-and-Floating-Point"></a> |
| <h3 class="section">17.23 Cross Compilation and Floating Point</h3> |
| <a name="index-cross-compilation-and-floating-point"></a> |
| <a name="index-floating-point-and-cross-compilation"></a> |
| |
| <p>While all modern machines use twos-complement representation for integers, |
| there are a variety of representations for floating point numbers. This |
| means that in a cross-compiler the representation of floating point numbers |
| in the compiled program may be different from that used in the machine |
| doing the compilation. |
| </p> |
| <p>Because different representation systems may offer different amounts of |
| range and precision, all floating point constants must be represented in |
| the target machine’s format. Therefore, the cross compiler cannot |
| safely use the host machine’s floating point arithmetic; it must emulate |
| the target’s arithmetic. To ensure consistency, GCC always uses |
| emulation to work with floating point values, even when the host and |
| target floating point formats are identical. |
| </p> |
| <p>The following macros are provided by <samp>real.h</samp> for the compiler to |
| use. All parts of the compiler which generate or optimize |
| floating-point calculations must use these macros. They may evaluate |
| their operands more than once, so operands must not have side effects. |
| </p> |
| <dl> |
| <dt><a name="index-REAL_005fVALUE_005fTYPE"></a>Macro: <strong>REAL_VALUE_TYPE</strong></dt> |
| <dd><p>The C data type to be used to hold a floating point value in the target |
| machine’s format. Typically this is a <code>struct</code> containing an |
| array of <code>HOST_WIDE_INT</code>, but all code should treat it as an opaque |
| quantity. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-REAL_005fVALUES_005fEQUAL"></a>Macro: <em>int</em> <strong>REAL_VALUES_EQUAL</strong> <em>(REAL_VALUE_TYPE <var>x</var>, REAL_VALUE_TYPE <var>y</var>)</em></dt> |
| <dd><p>Compares for equality the two values, <var>x</var> and <var>y</var>. If the target |
| floating point format supports negative zeroes and/or NaNs, |
| ‘<samp>REAL_VALUES_EQUAL (-0.0, 0.0)</samp>’ is true, and |
| ‘<samp>REAL_VALUES_EQUAL (NaN, NaN)</samp>’ is false. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-REAL_005fVALUES_005fLESS"></a>Macro: <em>int</em> <strong>REAL_VALUES_LESS</strong> <em>(REAL_VALUE_TYPE <var>x</var>, REAL_VALUE_TYPE <var>y</var>)</em></dt> |
| <dd><p>Tests whether <var>x</var> is less than <var>y</var>. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-REAL_005fVALUE_005fFIX"></a>Macro: <em>HOST_WIDE_INT</em> <strong>REAL_VALUE_FIX</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt> |
| <dd><p>Truncates <var>x</var> to a signed integer, rounding toward zero. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-REAL_005fVALUE_005fUNSIGNED_005fFIX"></a>Macro: <em>unsigned HOST_WIDE_INT</em> <strong>REAL_VALUE_UNSIGNED_FIX</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt> |
| <dd><p>Truncates <var>x</var> to an unsigned integer, rounding toward zero. If |
| <var>x</var> is negative, returns zero. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-REAL_005fVALUE_005fATOF"></a>Macro: <em>REAL_VALUE_TYPE</em> <strong>REAL_VALUE_ATOF</strong> <em>(const char *<var>string</var>, enum machine_mode <var>mode</var>)</em></dt> |
| <dd><p>Converts <var>string</var> into a floating point number in the target machine’s |
| representation for mode <var>mode</var>. This routine can handle both |
| decimal and hexadecimal floating point constants, using the syntax |
| defined by the C language for both. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-REAL_005fVALUE_005fNEGATIVE"></a>Macro: <em>int</em> <strong>REAL_VALUE_NEGATIVE</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt> |
| <dd><p>Returns 1 if <var>x</var> is negative (including negative zero), 0 otherwise. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-REAL_005fVALUE_005fISINF"></a>Macro: <em>int</em> <strong>REAL_VALUE_ISINF</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt> |
| <dd><p>Determines whether <var>x</var> represents infinity (positive or negative). |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-REAL_005fVALUE_005fISNAN"></a>Macro: <em>int</em> <strong>REAL_VALUE_ISNAN</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt> |
| <dd><p>Determines whether <var>x</var> represents a “NaN” (not-a-number). |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-REAL_005fARITHMETIC"></a>Macro: <em>void</em> <strong>REAL_ARITHMETIC</strong> <em>(REAL_VALUE_TYPE <var>output</var>, enum tree_code <var>code</var>, REAL_VALUE_TYPE <var>x</var>, REAL_VALUE_TYPE <var>y</var>)</em></dt> |
| <dd><p>Calculates an arithmetic operation on the two floating point values |
| <var>x</var> and <var>y</var>, storing the result in <var>output</var> (which must be a |
| variable). |
| </p> |
| <p>The operation to be performed is specified by <var>code</var>. Only the |
| following codes are supported: <code>PLUS_EXPR</code>, <code>MINUS_EXPR</code>, |
| <code>MULT_EXPR</code>, <code>RDIV_EXPR</code>, <code>MAX_EXPR</code>, <code>MIN_EXPR</code>. |
| </p> |
| <p>If <code>REAL_ARITHMETIC</code> is asked to evaluate division by zero and the |
| target’s floating point format cannot represent infinity, it will call |
| <code>abort</code>. Callers should check for this situation first, using |
| <code>MODE_HAS_INFINITIES</code>. See <a href="Storage-Layout.html#Storage-Layout">Storage Layout</a>. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-REAL_005fVALUE_005fNEGATE"></a>Macro: <em>REAL_VALUE_TYPE</em> <strong>REAL_VALUE_NEGATE</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt> |
| <dd><p>Returns the negative of the floating point value <var>x</var>. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-REAL_005fVALUE_005fABS"></a>Macro: <em>REAL_VALUE_TYPE</em> <strong>REAL_VALUE_ABS</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt> |
| <dd><p>Returns the absolute value of <var>x</var>. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-REAL_005fVALUE_005fTO_005fINT"></a>Macro: <em>void</em> <strong>REAL_VALUE_TO_INT</strong> <em>(HOST_WIDE_INT <var>low</var>, HOST_WIDE_INT <var>high</var>, REAL_VALUE_TYPE <var>x</var>)</em></dt> |
| <dd><p>Converts a floating point value <var>x</var> into a double-precision integer |
| which is then stored into <var>low</var> and <var>high</var>. If the value is not |
| integral, it is truncated. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-REAL_005fVALUE_005fFROM_005fINT"></a>Macro: <em>void</em> <strong>REAL_VALUE_FROM_INT</strong> <em>(REAL_VALUE_TYPE <var>x</var>, HOST_WIDE_INT <var>low</var>, HOST_WIDE_INT <var>high</var>, enum machine_mode <var>mode</var>)</em></dt> |
| <dd><p>Converts a double-precision integer found in <var>low</var> and <var>high</var>, |
| into a floating point value which is then stored into <var>x</var>. The |
| value is truncated to fit in mode <var>mode</var>. |
| </p></dd></dl> |
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