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| author | AbigailBuccaneer <AbigailBuccaneer@users.noreply.github.com> | 2020-08-24 18:04:37 +0100 |
|---|---|---|
| committer | AbigailBuccaneer <AbigailBuccaneer@users.noreply.github.com> | 2020-08-24 18:52:08 +0100 |
| commit | 6995a2e1bac6812ec4f48b98cfaf321f75c320d8 (patch) | |
| tree | e185dbb951524cc11ab33af90ddb20d412e92733 /libraries | |
| parent | 0f2757f0004e20503b2c4ee587e16f6775ee14bf (diff) | |
| download | PrismLauncher-6995a2e1bac6812ec4f48b98cfaf321f75c320d8.tar.gz PrismLauncher-6995a2e1bac6812ec4f48b98cfaf321f75c320d8.tar.bz2 PrismLauncher-6995a2e1bac6812ec4f48b98cfaf321f75c320d8.zip | |
Avoid undefined behaviour when byteswapping
`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.
Diffstat (limited to 'libraries')
| -rw-r--r-- | libraries/classparser/src/javaendian.h | 27 |
1 files changed, 5 insertions, 22 deletions
diff --git a/libraries/classparser/src/javaendian.h b/libraries/classparser/src/javaendian.h index 6eb4de63..5a6e107b 100644 --- a/libraries/classparser/src/javaendian.h +++ b/libraries/classparser/src/javaendian.h @@ -22,21 +22,6 @@ inline uint16_t bigswap(uint16_t x) return x; } -inline int64_t bigswap(int64_t x) -{ - return x; -} - -inline int32_t bigswap(int32_t x) -{ - return x; -} - -inline int16_t bigswap(int16_t x) -{ - return x; -} - #else inline uint64_t bigswap(uint64_t x) { @@ -55,22 +40,20 @@ inline uint16_t bigswap(uint16_t x) return (x >> 8) | (x << 8); } +#endif + inline int64_t bigswap(int64_t x) { - return (x >> 56) | ((x << 40) & 0x00FF000000000000) | ((x << 24) & 0x0000FF0000000000) | - ((x << 8) & 0x000000FF00000000) | ((x >> 8) & 0x00000000FF000000) | - ((x >> 24) & 0x0000000000FF0000) | ((x >> 40) & 0x000000000000FF00) | (x << 56); + return static_cast<int64_t>(bigswap(static_cast<uint64_t>(x))); } inline int32_t bigswap(int32_t x) { - return (x >> 24) | ((x << 8) & 0x00FF0000) | ((x >> 8) & 0x0000FF00) | (x << 24); + return static_cast<int32_t>(bigswap(static_cast<uint32_t>(x))); } inline int16_t bigswap(int16_t x) { - return (x >> 8) | (x << 8); + return static_cast<int16_t>(bigswap(static_cast<uint16_t>(x))); } - -#endif } |