Warning: This file is not a C or C++ file. It does not have highlighting.
| 1 | //===---- Free-standing function to detect rounding mode --------*- C++ -*-===// |
|---|---|
| 2 | // |
| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| 4 | // See https://llvm.org/LICENSE.txt for license information. |
| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| 6 | // |
| 7 | //===----------------------------------------------------------------------===// |
| 8 | |
| 9 | #ifndef LLVM_LIBC_SRC___SUPPORT_FPUTIL_ROUNDING_MODE_H |
| 10 | #define LLVM_LIBC_SRC___SUPPORT_FPUTIL_ROUNDING_MODE_H |
| 11 | |
| 12 | #include "hdr/fenv_macros.h" |
| 13 | #include "src/__support/macros/attributes.h" // LIBC_INLINE |
| 14 | #include "src/__support/macros/config.h" |
| 15 | |
| 16 | namespace LIBC_NAMESPACE_DECL { |
| 17 | namespace fputil { |
| 18 | |
| 19 | // Quick free-standing test whether fegetround() == FE_UPWARD. |
| 20 | // Using the following observation: |
| 21 | // 1.0f + 2^-25 = 1.0f for FE_TONEAREST, FE_DOWNWARD, FE_TOWARDZERO |
| 22 | // = 0x1.000002f for FE_UPWARD. |
| 23 | LIBC_INLINE bool fenv_is_round_up() { |
| 24 | volatile float x = 0x1.0p-25f; |
| 25 | return (1.0f + x != 1.0f); |
| 26 | } |
| 27 | |
| 28 | // Quick free-standing test whether fegetround() == FE_DOWNWARD. |
| 29 | // Using the following observation: |
| 30 | // -1.0f - 2^-25 = -1.0f for FE_TONEAREST, FE_UPWARD, FE_TOWARDZERO |
| 31 | // = -0x1.000002f for FE_DOWNWARD. |
| 32 | LIBC_INLINE bool fenv_is_round_down() { |
| 33 | volatile float x = 0x1.0p-25f; |
| 34 | return (-1.0f - x != -1.0f); |
| 35 | } |
| 36 | |
| 37 | // Quick free-standing test whether fegetround() == FE_TONEAREST. |
| 38 | // Using the following observation: |
| 39 | // 1.5f + 2^-24 = 1.5f for FE_TONEAREST, FE_DOWNWARD, FE_TOWARDZERO |
| 40 | // = 0x1.100002p0f for FE_UPWARD, |
| 41 | // 1.5f - 2^-24 = 1.5f for FE_TONEAREST, FE_UPWARD |
| 42 | // = 0x1.0ffffep-1f for FE_DOWNWARD, FE_TOWARDZERO |
| 43 | LIBC_INLINE bool fenv_is_round_to_nearest() { |
| 44 | static volatile float x = 0x1.0p-24f; |
| 45 | float y = x; |
| 46 | return (1.5f + y == 1.5f - y); |
| 47 | } |
| 48 | |
| 49 | // Quick free-standing test whether fegetround() == FE_TOWARDZERO. |
| 50 | // Using the following observation: |
| 51 | // 1.0f + 2^-23 + 2^-24 = 0x1.000002p0f for FE_DOWNWARD, FE_TOWARDZERO |
| 52 | // = 0x1.000004p0f for FE_TONEAREST, FE_UPWARD, |
| 53 | // -1.0f - 2^-24 = -1.0f for FE_TONEAREST, FE_UPWARD, FE_TOWARDZERO |
| 54 | // = -0x1.000002p0f for FE_DOWNWARD |
| 55 | // So: |
| 56 | // (0x1.000002p0f + 2^-24) + (-1.0f - 2^-24) = 2^-23 for FE_TOWARDZERO |
| 57 | // = 2^-22 for FE_TONEAREST, FE_UPWARD |
| 58 | // = 0 for FE_DOWNWARD |
| 59 | LIBC_INLINE bool fenv_is_round_to_zero() { |
| 60 | static volatile float x = 0x1.0p-24f; |
| 61 | float y = x; |
| 62 | return ((0x1.000002p0f + y) + (-1.0f - y) == 0x1.0p-23f); |
| 63 | } |
| 64 | |
| 65 | // Quick free standing get rounding mode based on the above observations. |
| 66 | LIBC_INLINE int quick_get_round() { |
| 67 | static volatile float x = 0x1.0p-24f; |
| 68 | float y = x; |
| 69 | float z = (0x1.000002p0f + y) + (-1.0f - y); |
| 70 | |
| 71 | if (z == 0.0f) |
| 72 | return FE_DOWNWARD; |
| 73 | if (z == 0x1.0p-23f) |
| 74 | return FE_TOWARDZERO; |
| 75 | return (2.0f + y == 2.0f) ? FE_TONEAREST : FE_UPWARD; |
| 76 | } |
| 77 | |
| 78 | } // namespace fputil |
| 79 | } // namespace LIBC_NAMESPACE_DECL |
| 80 | |
| 81 | #endif // LLVM_LIBC_SRC___SUPPORT_FPUTIL_ROUNDING_MODE_H |
| 82 |
Warning: This file is not a C or C++ file. It does not have highlighting.