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1//===-- Fast rounding to nearest integer for floating point -----*- 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-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef LLVM_LIBC_SRC___SUPPORT_FPUTIL_NEAREST_INTEGER_H10#define LLVM_LIBC_SRC___SUPPORT_FPUTIL_NEAREST_INTEGER_H11 12#include "src/__support/macros/config.h"13#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY14#include "src/__support/macros/properties/architectures.h"15#include "src/__support/macros/properties/cpu_features.h"16 17#if (defined(LIBC_TARGET_ARCH_IS_X86_64) && defined(LIBC_TARGET_CPU_HAS_SSE4_2))18#include "x86_64/nearest_integer.h"19#elif (defined(LIBC_TARGET_ARCH_IS_AARCH64) && defined(__ARM_FP))20#include "aarch64/nearest_integer.h"21#elif defined(LIBC_TARGET_ARCH_IS_GPU)22 23namespace LIBC_NAMESPACE_DECL {24namespace fputil {25 26LIBC_INLINE float nearest_integer(float x) { return __builtin_rintf(x); }27 28LIBC_INLINE double nearest_integer(double x) { return __builtin_rint(x); }29 30} // namespace fputil31} // namespace LIBC_NAMESPACE_DECL32 33#else34 35namespace LIBC_NAMESPACE_DECL {36namespace fputil {37 38// This is a fast implementation for rounding to a nearest integer that.39//40// Notice that for AARCH64 and x86-64 with SSE4.2 support, we will use their41// corresponding rounding instruction instead. And in those cases, the results42// are rounded to the nearest integer, tie-to-even.43LIBC_INLINE static constexpr float nearest_integer(float x) {44 if (x < 0x1p24f && x > -0x1p24f) {45 float r = x < 0 ? (x - 0x1.0p23f) + 0x1.0p23f : (x + 0x1.0p23f) - 0x1.0p23f;46 float diff = x - r;47 // The expression above is correct for the default rounding mode, round-to-48 // nearest, tie-to-even. For other rounding modes, it might be off by 1,49 // which is corrected below.50 if (LIBC_UNLIKELY(diff > 0.5f))51 return r + 1.0f;52 if (LIBC_UNLIKELY(diff < -0.5f))53 return r - 1.0f;54 return r;55 }56 return x;57}58 59LIBC_INLINE static constexpr double nearest_integer(double x) {60 if (x < 0x1p53 && x > -0x1p53) {61 double r = x < 0 ? (x - 0x1.0p52) + 0x1.0p52 : (x + 0x1.0p52) - 0x1.0p52;62 double diff = x - r;63 // The expression above is correct for the default rounding mode, round-to-64 // nearest, tie-to-even. For other rounding modes, it might be off by 1,65 // which is corrected below.66 if (LIBC_UNLIKELY(diff > 0.5))67 return r + 1.0;68 if (LIBC_UNLIKELY(diff < -0.5))69 return r - 1.0;70 return r;71 }72 return x;73}74 75} // namespace fputil76} // namespace LIBC_NAMESPACE_DECL77 78#endif79#endif // LLVM_LIBC_SRC___SUPPORT_FPUTIL_NEAREST_INTEGER_H80