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Merge pull request #17217 from maribu/core/bitarithm

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core/bitarthm: suppress false positives
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chrysn 2021-11-18 10:31:21 +01:00 committed by GitHub
commit 69af236d50
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1 changed files with 8 additions and 0 deletions
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core/include/bitarithm.h
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@ -172,6 +172,10 @@ static inline unsigned bitarithm_lsb(unsigned v)
{ {
/* Source: http://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightMultLookup */ /* Source: http://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightMultLookup */
extern const uint8_t MultiplyDeBruijnBitPosition[32]; extern const uint8_t MultiplyDeBruijnBitPosition[32];
/* cppcheck-suppress oppositeExpression
* (reason: `x & -x` is a bit twiddling idiom to extract the LSB; the
* check treats opposite arguments as indicator for poor copy-pasting
* as e.g. `x + -x` or `x & ~x` don't make sense. ) */
return MultiplyDeBruijnBitPosition[((uint32_t)((v & -v) * 0x077CB531U)) >> return MultiplyDeBruijnBitPosition[((uint32_t)((v & -v) * 0x077CB531U)) >>
27]; 27];
} }
@ -216,6 +220,10 @@ static inline unsigned bitarithm_test_and_clear(unsigned state, uint8_t *index)
#elif defined(BITARITHM_LSB_LOOKUP) #elif defined(BITARITHM_LSB_LOOKUP)
/* Source: http://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightMultLookup */ /* Source: http://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightMultLookup */
extern const uint8_t MultiplyDeBruijnBitPosition[32]; extern const uint8_t MultiplyDeBruijnBitPosition[32];
/* cppcheck-suppress oppositeExpression
* (reason: `x & -x` is a bit twiddling idiom to extract the LSB; the
* check treats opposite arguments as indicator for poor copy-pasting
* as e.g. `x + -x` or `x & ~x` don't make sense. ) */
uint32_t least_bit = state & -state; uint32_t least_bit = state & -state;
*index = MultiplyDeBruijnBitPosition[(least_bit * 0x077CB531U) >> 27]; *index = MultiplyDeBruijnBitPosition[(least_bit * 0x077CB531U) >> 27];
return state & ~least_bit; return state & ~least_bit;