6995a2e1ba
`a << b` is undefined when `a` is negative, and `a >> b` is implementation-defined. The correct thing to do here is to cast to unsigned, swap the bytes there and then swap back. This also improves performance on some compilers: Clang is smart enough to recognise that we're byteswapping here and reduce it to a single `bswap` instruction on x86_64, but only for the unsigned versions.
60 lines
1.1 KiB
C++
60 lines
1.1 KiB
C++
#pragma once
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#include <stdint.h>
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/**
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* Swap bytes between big endian and local number representation
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*/
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namespace util
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{
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#ifdef MULTIMC_BIG_ENDIAN
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inline uint64_t bigswap(uint64_t x)
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{
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return x;
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}
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inline uint32_t bigswap(uint32_t x)
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{
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return x;
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}
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inline uint16_t bigswap(uint16_t x)
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{
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return x;
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}
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#else
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inline uint64_t bigswap(uint64_t x)
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{
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return (x >> 56) | ((x << 40) & 0x00FF000000000000) | ((x << 24) & 0x0000FF0000000000) |
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((x << 8) & 0x000000FF00000000) | ((x >> 8) & 0x00000000FF000000) |
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((x >> 24) & 0x0000000000FF0000) | ((x >> 40) & 0x000000000000FF00) | (x << 56);
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}
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inline uint32_t bigswap(uint32_t x)
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{
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return (x >> 24) | ((x << 8) & 0x00FF0000) | ((x >> 8) & 0x0000FF00) | (x << 24);
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}
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inline uint16_t bigswap(uint16_t x)
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{
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return (x >> 8) | (x << 8);
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}
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#endif
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inline int64_t bigswap(int64_t x)
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{
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return static_cast<int64_t>(bigswap(static_cast<uint64_t>(x)));
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}
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inline int32_t bigswap(int32_t x)
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{
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return static_cast<int32_t>(bigswap(static_cast<uint32_t>(x)));
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}
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inline int16_t bigswap(int16_t x)
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{
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return static_cast<int16_t>(bigswap(static_cast<uint16_t>(x)));
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}
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}
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