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bitarithm: Move extern const out of static inline functions

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Workaround-For: https://github.com/immunant/c2rust/issues/423
This commit is contained in:
chrysn 2022-05-29 13:39:03 +02:00
parent 2d67eaf7ef
commit bdbde49753
2 changed files with 17 additions and 5 deletions
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2
core/lib/bitarithm.c
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@ -62,7 +62,7 @@ uint8_t bitarithm_bits_set_u32(uint32_t v)
} }
#endif #endif
const uint8_t MultiplyDeBruijnBitPosition[32] = const uint8_t bitarithm_MultiplyDeBruijnBitPosition[32] =
{ {
0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8, 0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9 31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9

20
core/lib/include/bitarithm.h
View File

@ -163,6 +163,20 @@ static inline unsigned bitarithm_msb(unsigned v)
#endif #endif
} }
/**
* @private
*
* @brief Lookup table for a fast CLS / LSB implementations.
*
* This is not supposed to be public, and should be declared `extern const` in
* the two functions which use it -- but that causes [transpiler issues], so it
* is declared here as a workaround. (Once that issue is resolved and part of
* CI, this line will be removed again).
*
* [transpiler issues]: https://github.com/immunant/c2rust/issues/423
*/
extern const uint8_t bitarithm_MultiplyDeBruijnBitPosition[32];
static inline unsigned bitarithm_lsb(unsigned v) static inline unsigned bitarithm_lsb(unsigned v)
#if defined(BITARITHM_LSB_BUILTIN) #if defined(BITARITHM_LSB_BUILTIN)
{ {
@ -171,12 +185,11 @@ static inline unsigned bitarithm_lsb(unsigned v)
#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];
/* cppcheck-suppress oppositeExpression /* cppcheck-suppress oppositeExpression
* (reason: `x & -x` is a bit twiddling idiom to extract the LSB; the * (reason: `x & -x` is a bit twiddling idiom to extract the LSB; the
* check treats opposite arguments as indicator for poor copy-pasting * check treats opposite arguments as indicator for poor copy-pasting
* as e.g. `x + -x` or `x & ~x` don't make sense. ) */ * as e.g. `x + -x` or `x & ~x` don't make sense. ) */
return MultiplyDeBruijnBitPosition[((uint32_t)((v & -v) * 0x077CB531U)) >> return bitarithm_MultiplyDeBruijnBitPosition[((uint32_t)((v & -v) * 0x077CB531U)) >>
27]; 27];
} }
#else #else
@ -219,13 +232,12 @@ static inline unsigned bitarithm_test_and_clear(unsigned state, uint8_t *index)
return state & ~(1 << *index); return state & ~(1 << *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];
/* cppcheck-suppress oppositeExpression /* cppcheck-suppress oppositeExpression
* (reason: `x & -x` is a bit twiddling idiom to extract the LSB; the * (reason: `x & -x` is a bit twiddling idiom to extract the LSB; the
* check treats opposite arguments as indicator for poor copy-pasting * check treats opposite arguments as indicator for poor copy-pasting
* as e.g. `x + -x` or `x & ~x` don't make sense. ) */ * 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 = bitarithm_MultiplyDeBruijnBitPosition[(least_bit * 0x077CB531U) >> 27];
return state & ~least_bit; return state & ~least_bit;
#else #else
while ((state & 1) == 0) { while ((state & 1) == 0) {