diff options
author | Christopher Haster <chaster@utexas.edu> | 2018-01-28 18:56:06 +0300 |
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committer | Christopher Haster <chaster@utexas.edu> | 2018-02-19 10:39:04 +0300 |
commit | 4f08424b51c6e7fda140b91fd551a35531ca0fc3 (patch) | |
tree | e4d738ba2dc9cbba5db783389d2ee5bc6315ae19 /lfs_util.h | |
parent | 59ce49fa4b9345364714168363069ca701feee0d (diff) |
Added software implementations of bitwise instructions
This helps significantly with supporting different compilers. Intrinsics for
different compilers can be added as they are found.
Note that for ARMCC, __builtin_ctz is not used. This was the result of a
strange issue where ARMCC only emits __builtin_ctz when passed the
--gnu flag, but __builtin_clz and __builtin_popcount are always emitted.
This isn't a big problem since the ARM instruction set doesn't have a
ctz instruction, and the npw2 based implementation is one of the most
efficient.
Also note that for littefs's purposes, we consider ctz(0) to be
undefined. This lets us save a branch in the software lfs_ctz
implementation.
Diffstat (limited to 'lfs_util.h')
-rw-r--r-- | lfs_util.h | 29 |
1 files changed, 25 insertions, 4 deletions
@@ -33,16 +33,37 @@ static inline uint32_t lfs_min(uint32_t a, uint32_t b) { return (a < b) ? a : b; } -static inline uint32_t lfs_ctz(uint32_t a) { - return __builtin_ctz(a); -} - static inline uint32_t lfs_npw2(uint32_t a) { +#if defined(__GNUC__) || defined(__CC_ARM) return 32 - __builtin_clz(a-1); +#else + uint32_t r = 0; + uint32_t s; + a -= 1; + s = (a > 0xffff) << 4; a >>= s; r |= s; + s = (a > 0xff ) << 3; a >>= s; r |= s; + s = (a > 0xf ) << 2; a >>= s; r |= s; + s = (a > 0x3 ) << 1; a >>= s; r |= s; + return (r | (a >> 1)) + 1; +#endif +} + +static inline uint32_t lfs_ctz(uint32_t a) { +#if defined(__GNUC__) + return __builtin_ctz(a); +#else + return lfs_npw2((a & -a) + 1) - 1; +#endif } static inline uint32_t lfs_popc(uint32_t a) { +#if defined(__GNUC__) || defined(__CC_ARM) return __builtin_popcount(a); +#else + a = a - ((a >> 1) & 0x55555555); + a = (a & 0x33333333) + ((a >> 2) & 0x33333333); + return (((a + (a >> 4)) & 0xf0f0f0f) * 0x1010101) >> 24; +#endif } static inline int lfs_scmp(uint32_t a, uint32_t b) { |