llvm/libc/src/__support/FPUtil/rounding_mode.h

//===---- Free-standing function to detect rounding mode --------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_LIBC_SRC___SUPPORT_FPUTIL_ROUNDING_MODE_H
#define LLVM_LIBC_SRC___SUPPORT_FPUTIL_ROUNDING_MODE_H

#include "hdr/fenv_macros.h"
#include "src/__support/macros/attributes.h" // LIBC_INLINE
#include "src/__support/macros/config.h"

namespace LIBC_NAMESPACE_DECL {
namespace fputil {

// Quick free-standing test whether fegetround() == FE_UPWARD.
// Using the following observation:
//   1.0f + 2^-25 = 1.0f        for FE_TONEAREST, FE_DOWNWARD, FE_TOWARDZERO
//                = 0x1.000002f for FE_UPWARD.
LIBC_INLINE bool fenv_is_round_up() { … }

// Quick free-standing test whether fegetround() == FE_DOWNWARD.
// Using the following observation:
//   -1.0f - 2^-25 = -1.0f        for FE_TONEAREST, FE_UPWARD, FE_TOWARDZERO
//                 = -0x1.000002f for FE_DOWNWARD.
LIBC_INLINE bool fenv_is_round_down() { … }

// Quick free-standing test whether fegetround() == FE_TONEAREST.
// Using the following observation:
//   1.5f + 2^-24 = 1.5f           for FE_TONEAREST, FE_DOWNWARD, FE_TOWARDZERO
//                = 0x1.100002p0f  for FE_UPWARD,
//   1.5f - 2^-24 = 1.5f           for FE_TONEAREST, FE_UPWARD
//                = 0x1.0ffffep-1f for FE_DOWNWARD, FE_TOWARDZERO
LIBC_INLINE bool fenv_is_round_to_nearest() { … }

// Quick free-standing test whether fegetround() == FE_TOWARDZERO.
// Using the following observation:
//   1.0f + 2^-23 + 2^-24 = 0x1.000002p0f for FE_DOWNWARD, FE_TOWARDZERO
//                        = 0x1.000004p0f for FE_TONEAREST, FE_UPWARD,
//  -1.0f - 2^-24 = -1.0f          for FE_TONEAREST, FE_UPWARD, FE_TOWARDZERO
//                = -0x1.000002p0f for FE_DOWNWARD
// So:
// (0x1.000002p0f + 2^-24) + (-1.0f - 2^-24) = 2^-23 for FE_TOWARDZERO
//                                           = 2^-22 for FE_TONEAREST, FE_UPWARD
//                                           = 0 for FE_DOWNWARD
LIBC_INLINE bool fenv_is_round_to_zero() { … }

// Quick free standing get rounding mode based on the above observations.
LIBC_INLINE int quick_get_round() { … }

} // namespace fputil
} // namespace LIBC_NAMESPACE_DECL

#endif // LLVM_LIBC_SRC___SUPPORT_FPUTIL_ROUNDING_MODE_H