1 //===-- Abstract class for bit manipulation of float 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_UTILS_FPUTIL_FP_BITS_H 10 #define LLVM_LIBC_UTILS_FPUTIL_FP_BITS_H 11 12 #include "utils/CPP/TypeTraits.h" 13 14 #include <stdint.h> 15 16 namespace __llvm_libc { 17 namespace fputil { 18 19 template <typename T> struct MantissaWidth {}; 20 template <> struct MantissaWidth<float> { 21 static constexpr unsigned value = 23; 22 }; 23 template <> struct MantissaWidth<double> { 24 static constexpr unsigned value = 52; 25 }; 26 27 template <typename T> struct ExponentWidth {}; 28 template <> struct ExponentWidth<float> { 29 static constexpr unsigned value = 8; 30 }; 31 template <> struct ExponentWidth<double> { 32 static constexpr unsigned value = 11; 33 }; 34 template <> struct ExponentWidth<long double> { 35 static constexpr unsigned value = 15; 36 }; 37 38 template <typename T> struct FPUIntType {}; 39 template <> struct FPUIntType<float> { using Type = uint32_t; }; 40 template <> struct FPUIntType<double> { using Type = uint64_t; }; 41 42 #if !(defined(__x86_64__) || defined(__i386__)) 43 // TODO: This has to be extended for visual studio where long double and 44 // double are equivalent. 45 template <> struct MantissaWidth<long double> { 46 static constexpr unsigned value = 112; 47 }; 48 49 template <> struct FPUIntType<long double> { using Type = __uint128_t; }; 50 #endif 51 52 // A generic class to represent single precision, double precision, and quad 53 // precision IEEE 754 floating point formats. 54 // On most platforms, the 'float' type corresponds to single precision floating 55 // point numbers, the 'double' type corresponds to double precision floating 56 // point numers, and the 'long double' type corresponds to the quad precision 57 // floating numbers. On x86 platforms however, the 'long double' type maps to 58 // an x87 floating point format. This format is an IEEE 754 extension format. 59 // It is handled as an explicit specialization of this class. 60 template <typename T> struct __attribute__((packed)) FPBits { 61 static_assert(cpp::IsFloatingPointType<T>::Value, 62 "FPBits instantiated with invalid type."); 63 64 // Reinterpreting bits as an integer value and interpreting the bits of an 65 // integer value as a floating point value is used in tests. So, a convenient 66 // type is provided for such reinterpretations. 67 using UIntType = typename FPUIntType<T>::Type; 68 69 UIntType mantissa : MantissaWidth<T>::value; 70 uint16_t exponent : ExponentWidth<T>::value; 71 uint8_t sign : 1; 72 73 static constexpr int exponentBias = (1 << (ExponentWidth<T>::value - 1)) - 1; 74 static constexpr int maxExponent = (1 << ExponentWidth<T>::value) - 1; 75 76 static constexpr UIntType minSubnormal = UIntType(1); 77 static constexpr UIntType maxSubnormal = 78 (UIntType(1) << MantissaWidth<T>::value) - 1; 79 static constexpr UIntType minNormal = 80 (UIntType(1) << MantissaWidth<T>::value); 81 static constexpr UIntType maxNormal = 82 ((UIntType(maxExponent) - 1) << MantissaWidth<T>::value) | maxSubnormal; 83 84 // We don't want accidental type promotions/conversions so we require exact 85 // type match. 86 template <typename XType, 87 cpp::EnableIfType<cpp::IsSame<T, XType>::Value || 88 (cpp::IsIntegral<XType>::Value && 89 (sizeof(XType) == sizeof(UIntType))), 90 int> = 0> 91 explicit FPBits(XType x) { 92 *this = *reinterpret_cast<FPBits<T> *>(&x); 93 } 94 95 operator T() { return *reinterpret_cast<T *>(this); } 96 97 int getExponent() const { return int(exponent) - exponentBias; } 98 99 bool isZero() const { return mantissa == 0 && exponent == 0; } 100 101 bool isInf() const { return mantissa == 0 && exponent == maxExponent; } 102 103 bool isNaN() const { return exponent == maxExponent && mantissa != 0; } 104 105 bool isInfOrNaN() const { return exponent == maxExponent; } 106 107 // Methods below this are used by tests. 108 // The to and from integer bits converters are only used in tests. Hence, 109 // the potential software implementations of UIntType will not slow real 110 // code. 111 112 UIntType bitsAsUInt() const { 113 return *reinterpret_cast<const UIntType *>(this); 114 } 115 116 static FPBits<T> zero() { return FPBits(T(0.0)); } 117 118 static FPBits<T> negZero() { 119 FPBits<T> bits(T(0.0)); 120 bits.sign = 1; 121 return bits; 122 } 123 124 static FPBits<T> inf() { 125 FPBits<T> bits(T(0.0)); 126 bits.exponent = maxExponent; 127 return bits; 128 } 129 130 static FPBits<T> negInf() { 131 FPBits<T> bits(T(0.0)); 132 bits.exponent = maxExponent; 133 bits.sign = 1; 134 return bits; 135 } 136 137 static T buildNaN(UIntType v) { 138 FPBits<T> bits(T(0.0)); 139 bits.exponent = maxExponent; 140 bits.mantissa = v; 141 return bits; 142 } 143 }; 144 145 } // namespace fputil 146 } // namespace __llvm_libc 147 148 #if defined(__x86_64__) || defined(__i386__) 149 #include "utils/FPUtil/LongDoubleBitsX86.h" 150 #endif 151 152 #endif // LLVM_LIBC_UTILS_FPUTIL_FP_BITS_H 153