github-mirrors/thirdparty-littlefs
1
0
Fork 0
mirror of https://github.com/eledio-devices/thirdparty-littlefs.git synced 2025-10-31 00:32:38 +01:00
Code Issues Packages Projects Releases Wiki Activity

Added software implementations of bitwise instructions

Browse Source 
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.
This commit is contained in:
Christopher Haster
2018-01-28 09:56:06 -06:00
parent 59ce49fa4b
commit 4f08424b51
1 changed files with 25 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

29
lfs_util.h
View File

@@ -33,16 +33,37 @@ static inline uint32_t lfs_min(uint32_t a, uint32_t b) {
return (a < b) ? a : b; return (a < b) ? a : b;
} }
static inline uint32_t lfs_ctz(uint32_t a) { static inline uint32_t lfs_npw2(uint32_t a) {
return __builtin_ctz(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_npw2(uint32_t a) { static inline uint32_t lfs_ctz(uint32_t a) {
return 32 - __builtin_clz(a-1); #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) { static inline uint32_t lfs_popc(uint32_t a) {
#if defined(__GNUC__) || defined(__CC_ARM)
return __builtin_popcount(a); 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) { static inline int lfs_scmp(uint32_t a, uint32_t b) {