projects / thirdparty / gcc.git / blame
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| c63539ff ML |
1 | .. |
| 2 | Copyright 1988-2022 Free Software Foundation, Inc. | |
| 3 | This is part of the GCC manual. | |
| 4 | For copying conditions, see the copyright.rst file. | |
| 5 | ||
| 6 | .. _floating-point-implementation: | |
| 7 | ||
| 8 | Floating Point | |
| 9 | ************** | |
| 10 | ||
| 11 | * The accuracy of the floating-point operations and of the library | |
| 12 | functions in ``<math.h>`` and ``<complex.h>`` that return floating-point | |
| 13 | results (C90, C99 and C11 5.2.4.2.2). | |
| 14 | ||
| 15 | The accuracy is unknown. | |
| 16 | ||
| 17 | * The rounding behaviors characterized by non-standard values | |
| 18 | of ``FLT_ROUNDS`` | |
| 19 | (C90, C99 and C11 5.2.4.2.2). | |
| 20 | ||
| 21 | GCC does not use such values. | |
| 22 | ||
| 23 | * The evaluation methods characterized by non-standard negative | |
| 24 | values of ``FLT_EVAL_METHOD`` (C99 and C11 5.2.4.2.2). | |
| 25 | ||
| 26 | GCC does not use such values. | |
| 27 | ||
| 28 | * The direction of rounding when an integer is converted to a | |
| 29 | floating-point number that cannot exactly represent the original | |
| 30 | value (C90 6.2.1.3, C99 and C11 6.3.1.4). | |
| 31 | ||
| 32 | C99 Annex F is followed. | |
| 33 | ||
| 34 | * The direction of rounding when a floating-point number is | |
| 35 | converted to a narrower floating-point number (C90 6.2.1.4, C99 and C11 | |
| 36 | 6.3.1.5). | |
| 37 | ||
| 38 | C99 Annex F is followed. | |
| 39 | ||
| 40 | * How the nearest representable value or the larger or smaller | |
| 41 | representable value immediately adjacent to the nearest representable | |
| 42 | value is chosen for certain floating constants (C90 6.1.3.1, C99 and C11 | |
| 43 | 6.4.4.2). | |
| 44 | ||
| 45 | C99 Annex F is followed. | |
| 46 | ||
| 47 | * Whether and how floating expressions are contracted when not | |
| 48 | disallowed by the ``FP_CONTRACT`` pragma (C99 and C11 6.5). | |
| 49 | ||
| 50 | Expressions are currently only contracted if :option:`-ffp-contract=fast`, | |
| 51 | :option:`-funsafe-math-optimizations` or :option:`-ffast-math` are used. | |
| 52 | This is subject to change. | |
| 53 | ||
| 54 | * The default state for the ``FENV_ACCESS`` pragma (C99 and C11 | |
| 55 | 7.6.1). | |
| 56 | ||
| 57 | This pragma is not implemented, but the default is to 'off' unless | |
| 58 | :option:`-frounding-math` is used and :option:`-fno-trapping-math` is not | |
| 59 | in which case it is 'on'. | |
| 60 | ||
| 61 | * Additional floating-point exceptions, rounding modes, environments, | |
| 62 | and classifications, and their macro names (C99 and C11 7.6, C99 and | |
| 63 | C11 7.12). | |
| 64 | ||
| 65 | This is dependent on the implementation of the C library, and is not | |
| 66 | defined by GCC itself. | |
| 67 | ||
| 68 | * The default state for the ``FP_CONTRACT`` pragma (C99 and C11 | |
| 69 | 7.12.2). | |
| 70 | ||
| 71 | This pragma is not implemented. Expressions are currently only | |
| 72 | contracted if :option:`-ffp-contract=fast`, | |
| 73 | :option:`-funsafe-math-optimizations` or :option:`-ffast-math` are used. | |
| 74 | This is subject to change. | |
| 75 | ||
| 76 | * Whether the 'inexact' floating-point exception can be raised | |
| 77 | when the rounded result actually does equal the mathematical result | |
| 78 | in an IEC 60559 conformant implementation (C99 F.9). | |
| 79 | ||
| 80 | This is dependent on the implementation of the C library, and is not | |
| 81 | defined by GCC itself. | |
| 82 | ||
| 83 | * Whether the 'underflow' (and 'inexact') floating-point | |
| 84 | exception can be raised when a result is tiny but not inexact in an | |
| 85 | IEC 60559 conformant implementation (C99 F.9). | |
| 86 | ||
| 87 | This is dependent on the implementation of the C library, and is not | |
| a0ccbac8 | 88 | defined by GCC itself. |