1//===-- nextafter implementation for x86 long double numbers ----*- 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_X86_64_NEXTAFTERLONGDOUBLE_H
10#define LLVM_LIBC_SRC___SUPPORT_FPUTIL_X86_64_NEXTAFTERLONGDOUBLE_H
11
12#include "src/__support/macros/properties/architectures.h"
13
14#if !defined(LIBC_TARGET_ARCH_IS_X86)
15#error "Invalid include"
16#endif
17
18#include "src/__support/CPP/bit.h"
19#include "src/__support/FPUtil/FEnvImpl.h"
20#include "src/__support/FPUtil/FPBits.h"
21
22#include <stdint.h>
23
24namespace LIBC_NAMESPACE {
25namespace fputil {
26
27LIBC_INLINE long double nextafter(long double from, long double to) {
28 using FPBits = FPBits<long double>;
29 FPBits from_bits(from);
30 if (from_bits.is_nan())
31 return from;
32
33 FPBits to_bits(to);
34 if (to_bits.is_nan())
35 return to;
36
37 if (from == to)
38 return to;
39
40 // Convert pseudo subnormal number to normal number.
41 if (from_bits.get_implicit_bit() == 1 && from_bits.is_subnormal()) {
42 from_bits.set_biased_exponent(1);
43 }
44
45 using StorageType = FPBits::StorageType;
46
47 constexpr StorageType FRACTION_MASK = FPBits::FRACTION_MASK;
48 // StorageType int_val = from_bits.uintval();
49 if (from == 0.0l) { // +0.0 / -0.0
50 from_bits = FPBits::min_subnormal(sign: from > to ? Sign::NEG : Sign::POS);
51 } else if (from < 0.0l) {
52 if (to < from) { // toward -inf
53 if (from_bits == FPBits::max_subnormal(sign: Sign::NEG)) {
54 // We deal with normal/subnormal boundary separately to avoid
55 // dealing with the implicit bit.
56 from_bits = FPBits::min_normal(sign: Sign::NEG);
57 } else if (from_bits.get_mantissa() == FRACTION_MASK) {
58 from_bits.set_mantissa(0);
59 // Incrementing exponent might overflow the value to infinity,
60 // which is what is expected. Since NaNs are handling separately,
61 // it will never overflow "beyond" infinity.
62 from_bits.set_biased_exponent(from_bits.get_biased_exponent() + 1);
63 if (from_bits.is_inf())
64 raise_except_if_required(FE_OVERFLOW | FE_INEXACT);
65 return from_bits.get_val();
66 } else {
67 from_bits = FPBits(StorageType(from_bits.uintval() + 1));
68 }
69 } else { // toward +inf
70 if (from_bits == FPBits::min_normal(sign: Sign::NEG)) {
71 // We deal with normal/subnormal boundary separately to avoid
72 // dealing with the implicit bit.
73 from_bits = FPBits::max_subnormal(sign: Sign::NEG);
74 } else if (from_bits.get_mantissa() == 0) {
75 from_bits.set_mantissa(FRACTION_MASK);
76 // from == 0 is handled separately so decrementing the exponent will not
77 // lead to underflow.
78 from_bits.set_biased_exponent(from_bits.get_biased_exponent() - 1);
79 return from_bits.get_val();
80 } else {
81 from_bits = FPBits(StorageType(from_bits.uintval() - 1));
82 }
83 }
84 } else {
85 if (to < from) { // toward -inf
86 if (from_bits == FPBits::min_normal(sign: Sign::POS)) {
87 from_bits = FPBits::max_subnormal(sign: Sign::POS);
88 } else if (from_bits.get_mantissa() == 0) {
89 from_bits.set_mantissa(FRACTION_MASK);
90 // from == 0 is handled separately so decrementing the exponent will not
91 // lead to underflow.
92 from_bits.set_biased_exponent(from_bits.get_biased_exponent() - 1);
93 return from_bits.get_val();
94 } else {
95 from_bits = FPBits(StorageType(from_bits.uintval() - 1));
96 }
97 } else { // toward +inf
98 if (from_bits == FPBits::max_subnormal(sign: Sign::POS)) {
99 from_bits = FPBits::min_normal(sign: Sign::POS);
100 } else if (from_bits.get_mantissa() == FRACTION_MASK) {
101 from_bits.set_mantissa(0);
102 // Incrementing exponent might overflow the value to infinity,
103 // which is what is expected. Since NaNs are handling separately,
104 // it will never overflow "beyond" infinity.
105 from_bits.set_biased_exponent(from_bits.get_biased_exponent() + 1);
106 if (from_bits.is_inf())
107 raise_except_if_required(FE_OVERFLOW | FE_INEXACT);
108 return from_bits.get_val();
109 } else {
110 from_bits = FPBits(StorageType(from_bits.uintval() + 1));
111 }
112 }
113 }
114
115 if (!from_bits.get_implicit_bit())
116 raise_except_if_required(FE_UNDERFLOW | FE_INEXACT);
117
118 return from_bits.get_val();
119}
120
121} // namespace fputil
122} // namespace LIBC_NAMESPACE
123
124#endif // LLVM_LIBC_SRC___SUPPORT_FPUTIL_X86_64_NEXTAFTERLONGDOUBLE_H
125

source code of libc/src/__support/FPUtil/x86_64/NextAfterLongDouble.h