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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-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef LLVM_LIBC_SRC___SUPPORT_FPUTIL_NEAREST_INTEGER_H
10#define LLVM_LIBC_SRC___SUPPORT_FPUTIL_NEAREST_INTEGER_H
11
12#include "src/__support/macros/config.h"
13#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
14#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 fputil
31} // namespace LIBC_NAMESPACE_DECL
32
33#else
34
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 their
41// corresponding rounding instruction instead. And in those cases, the results
42// are rounded to the nearest integer, tie-to-even.
43LIBC_INLINE 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 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 fputil
76} // namespace LIBC_NAMESPACE_DECL
77
78#endif
79#endif // LLVM_LIBC_SRC___SUPPORT_FPUTIL_NEAREST_INTEGER_H
80

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source code of libc/src/__support/FPUtil/nearest_integer.h