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| <title>Using the GNU Compiler Collection (GCC): Floating point implementation</title> |
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| <a name="Floating-point-implementation"></a> |
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| <a name="Floating-point"></a> |
| <h3 class="section">4.6 Floating point</h3> |
| |
| <ul> |
| <li> <cite>The accuracy of the floating-point operations and of the library |
| functions in <code><math.h></code> and <code><complex.h></code> that return floating-point |
| results (C90, C99 and C11 5.2.4.2.2).</cite> |
| |
| <p>The accuracy is unknown. |
| </p> |
| </li><li> <cite>The rounding behaviors characterized by non-standard values |
| of <code>FLT_ROUNDS</code> |
| (C90, C99 and C11 5.2.4.2.2).</cite> |
| |
| <p>GCC does not use such values. |
| </p> |
| </li><li> <cite>The evaluation methods characterized by non-standard negative |
| values of <code>FLT_EVAL_METHOD</code> (C99 and C11 5.2.4.2.2).</cite> |
| |
| <p>GCC does not use such values. |
| </p> |
| </li><li> <cite>The direction of rounding when an integer is converted to a |
| floating-point number that cannot exactly represent the original |
| value (C90 6.2.1.3, C99 and C11 6.3.1.4).</cite> |
| |
| <p>C99 Annex F is followed. |
| </p> |
| </li><li> <cite>The direction of rounding when a floating-point number is |
| converted to a narrower floating-point number (C90 6.2.1.4, C99 and C11 |
| 6.3.1.5).</cite> |
| |
| <p>C99 Annex F is followed. |
| </p> |
| </li><li> <cite>How the nearest representable value or the larger or smaller |
| representable value immediately adjacent to the nearest representable |
| value is chosen for certain floating constants (C90 6.1.3.1, C99 and C11 |
| 6.4.4.2).</cite> |
| |
| <p>C99 Annex F is followed. |
| </p> |
| </li><li> <cite>Whether and how floating expressions are contracted when not |
| disallowed by the <code>FP_CONTRACT</code> pragma (C99 and C11 6.5).</cite> |
| |
| <p>Expressions are currently only contracted if <samp>-ffp-contract=fast</samp>, |
| <samp>-funsafe-math-optimizations</samp> or <samp>-ffast-math</samp> are used. |
| This is subject to change. |
| </p> |
| </li><li> <cite>The default state for the <code>FENV_ACCESS</code> pragma (C99 and C11 |
| 7.6.1).</cite> |
| |
| <p>This pragma is not implemented, but the default is to “off” unless |
| <samp>-frounding-math</samp> is used in which case it is “on”. |
| </p> |
| </li><li> <cite>Additional floating-point exceptions, rounding modes, environments, |
| and classifications, and their macro names (C99 and C11 7.6, C99 and |
| C11 7.12).</cite> |
| |
| <p>This is dependent on the implementation of the C library, and is not |
| defined by GCC itself. |
| </p> |
| </li><li> <cite>The default state for the <code>FP_CONTRACT</code> pragma (C99 and C11 |
| 7.12.2).</cite> |
| |
| <p>This pragma is not implemented. Expressions are currently only |
| contracted if <samp>-ffp-contract=fast</samp>, |
| <samp>-funsafe-math-optimizations</samp> or <samp>-ffast-math</samp> are used. |
| This is subject to change. |
| </p> |
| </li><li> <cite>Whether the “inexact” floating-point exception can be raised |
| when the rounded result actually does equal the mathematical result |
| in an IEC 60559 conformant implementation (C99 F.9).</cite> |
| |
| <p>This is dependent on the implementation of the C library, and is not |
| defined by GCC itself. |
| </p> |
| </li><li> <cite>Whether the “underflow” (and “inexact”) floating-point |
| exception can be raised when a result is tiny but not inexact in an |
| IEC 60559 conformant implementation (C99 F.9).</cite> |
| |
| <p>This is dependent on the implementation of the C library, and is not |
| defined by GCC itself. |
| </p> |
| </li></ul> |
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