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/architectures.h"
13 #include "src/__support/common.h"
14 
15 #if (defined(LLVM_LIBC_ARCH_X86_64) && defined(__SSE4_2__))
16 #include "x86_64/nearest_integer.h"
17 #elif defined(LLVM_LIBC_ARCH_AARCH64)
18 #include "aarch64/nearest_integer.h"
19 #else
20 
21 namespace __llvm_libc {
22 namespace fputil {
23 
24 // This is a fast implementation for rounding to a nearest integer that.
25 //
26 // Notice that for AARCH64 and x86-64 with SSE4.2 support, we will use their
27 // corresponding rounding instruction instead.  And in those cases, the results
28 // are rounded to the nearest integer, tie-to-even.
29 static inline float nearest_integer(float x) {
30   if (x < 0x1p24f && x > -0x1p24f) {
31     float r = x < 0 ? (x - 0x1.0p23f) + 0x1.0p23f : (x + 0x1.0p23f) - 0x1.0p23f;
32     float diff = x - r;
33     // The expression above is correct for the default rounding mode, round-to-
34     // nearest, tie-to-even.  For other rounding modes, it might be off by 1,
35     // which is corrected below.
36     if (unlikely(diff > 0.5f))
37       return r + 1.0f;
38     if (unlikely(diff < -0.5f))
39       return r - 1.0f;
40     return r;
41   }
42   return x;
43 }
44 
45 static inline double nearest_integer(double x) {
46   if (x < 0x1p53 && x > -0x1p53) {
47     double r = x < 0 ? (x - 0x1.0p52) + 0x1.0p52 : (x + 0x1.0p52) - 0x1.0p52;
48     double diff = x - r;
49     // The expression above is correct for the default rounding mode, round-to-
50     // nearest, tie-to-even.  For other rounding modes, it might be off by 1,
51     // which is corrected below.
52     if (unlikely(diff > 0.5))
53       return r + 1.0;
54     if (unlikely(diff < -0.5))
55       return r - 1.0;
56     return r;
57   }
58   return x;
59 }
60 
61 } // namespace fputil
62 } // namespace __llvm_libc
63 
64 #endif
65 #endif // LLVM_LIBC_SRC_SUPPORT_FPUTIL_NEAREST_INTEGER_H
66