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130 lines
4.2 KiB
C++
130 lines
4.2 KiB
C++
/*
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* Copyright (c) 2022, Jelle Raaijmakers <jelle@gmta.nl>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/Types.h>
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namespace AK {
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template<typename T>
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union FloatExtractor;
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#ifdef AK_HAS_FLOAT_128
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template<>
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union FloatExtractor<f128> {
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using ComponentType = unsigned __int128;
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static constexpr int mantissa_bits = 112;
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static constexpr ComponentType mantissa_max = (((ComponentType)1) << 112) - 1;
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static constexpr int exponent_bias = 16383;
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static constexpr int exponent_bits = 15;
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static constexpr unsigned exponent_max = 32767;
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struct [[gnu::packed]] {
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# if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
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ComponentType sign : 1;
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ComponentType exponent : 15;
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ComponentType mantissa : 112;
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# else
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ComponentType mantissa : 112;
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ComponentType exponent : 15;
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ComponentType sign : 1;
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# endif
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};
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f128 d;
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};
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// Validate that f128 and the FloatExtractor union are 128 bits.
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static_assert(AssertSize<f128, 16>());
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static_assert(AssertSize<FloatExtractor<f128>, sizeof(f128)>());
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#endif
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#ifdef AK_HAS_FLOAT_80
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template<>
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union FloatExtractor<f80> {
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using ComponentType = unsigned long long;
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static constexpr int mantissa_bits = 64;
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static constexpr ComponentType mantissa_max = ~0ull;
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static constexpr int exponent_bias = 16383;
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static constexpr int exponent_bits = 15;
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static constexpr unsigned exponent_max = 32767;
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struct [[gnu::packed]] {
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// This is technically wrong: Extended floating point values really only have 63 bits of mantissa
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// and an "integer bit" that behaves in various strange, unintuitive and non-IEEE-754 ways.
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// However, since all bit-fiddling float code assumes IEEE floats, it cannot handle this properly.
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// If we pretend that 80-bit floats are IEEE floats with 64-bit mantissas, almost everything works correctly
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// and we just need a few special cases.
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# if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
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ComponentType sign : 1;
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ComponentType exponent : 15;
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ComponentType mantissa : 64;
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# else
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ComponentType mantissa : 64;
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ComponentType exponent : 15;
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ComponentType sign : 1;
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# endif
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};
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f80 d;
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};
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static_assert(AssertSize<FloatExtractor<f80>, sizeof(f80)>());
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#endif
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template<>
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union FloatExtractor<f64> {
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using ComponentType = unsigned long long;
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static constexpr int mantissa_bits = 52;
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static constexpr ComponentType mantissa_max = (1ull << 52) - 1;
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static constexpr int exponent_bias = 1023;
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static constexpr int exponent_bits = 11;
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static constexpr unsigned exponent_max = 2047;
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struct [[gnu::packed]] {
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// FIXME: These types have to all be the same, otherwise this struct
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// goes from being a bitfield describing the layout of an f64
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// into being a multibyte mess on windows.
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// Technically, '-mno-ms-bitfields' is supposed to disable this
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// very intuitive and portable behaviour on windows, but it doesn't
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// work with the msvc ABI.
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// See <https://github.com/llvm/llvm-project/issues/24757>
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#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
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ComponentType sign : 1;
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ComponentType exponent : 11;
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ComponentType mantissa : 52;
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#else
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ComponentType mantissa : 52;
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ComponentType exponent : 11;
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ComponentType sign : 1;
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#endif
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};
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f64 d;
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};
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static_assert(AssertSize<FloatExtractor<f64>, sizeof(f64)>());
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template<>
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union FloatExtractor<f32> {
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using ComponentType = unsigned;
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static constexpr int mantissa_bits = 23;
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static constexpr ComponentType mantissa_max = (1 << 23) - 1;
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static constexpr int exponent_bias = 127;
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static constexpr int exponent_bits = 8;
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static constexpr ComponentType exponent_max = 255;
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struct [[gnu::packed]] {
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#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
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ComponentType sign : 1;
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ComponentType exponent : 8;
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ComponentType mantissa : 23;
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#else
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ComponentType mantissa : 23;
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ComponentType exponent : 8;
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ComponentType sign : 1;
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#endif
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};
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f32 d;
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};
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static_assert(AssertSize<FloatExtractor<f32>, sizeof(f32)>());
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}
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#if USING_AK_GLOBALLY
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using AK::FloatExtractor;
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#endif
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