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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 | |
23 | namespace LIBC_NAMESPACE_DECL { |
24 | namespace fputil { |
25 | |
26 | LIBC_INLINE float nearest_integer(float x) { return __builtin_rintf(x); } |
27 | |
28 | LIBC_INLINE double nearest_integer(double x) { return __builtin_rint(x); } |
29 | |
30 | } // namespace fputil |
31 | } // namespace LIBC_NAMESPACE_DECL |
32 | |
33 | #else |
34 | |
35 | namespace LIBC_NAMESPACE_DECL { |
36 | namespace 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. |
43 | LIBC_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 | |
59 | LIBC_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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