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arch: Simplify find_lsb_set() 

Rather than testing each bit until the lowest set bit is found, we can
massage the input parameter to easily clear all bits except the lowest
set bit. When only one bit is set, both find_lsb_set() and find_msb_set()
return the same value.

Signed-off-by: Peter Mitsis <peter.mitsis@intel.com>
This commit is contained in:
Peter Mitsis 2024-09-04 18:51:42 +00:00 committed by Henrik Brix Andersen
parent 3c092f9274
commit 03d9f636ea
1 changed files with 4 additions and 17 deletions
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21
include/zephyr/arch/common/ffs.h
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@ -57,26 +57,13 @@ static ALWAYS_INLINE unsigned int find_lsb_set(uint32_t op)
#else
/*
* Toolchain does not have __builtin_ffs().
* Need to do this manually.
* Toolchain does not have __builtin_ffs(). Leverage find_lsb_set()
* by first clearing all but the lowest set bit.
*/
int bit;
if (op == 0) {
return 0;
}
op = op ^ (op & (op - 1));
for (bit = 0; bit < 32; bit++) {
if ((op & (1 << bit)) != 0) {
return (bit + 1);
}
}
/*
* This should never happen but we need to keep
* compiler happy.
*/
return 0;
return find_msb_set(op);
#endif /* CONFIG_TOOLCHAIN_HAS_BUILTIN_FFS */
}