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MINOR: tools: implement my_flsl()

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We already have my_ffsl() to find the lowest bit set in a word, and
this patch implements the search for the highest bit set in a word.
On x86 it uses the bsr instruction and on other architectures it
uses an efficient implementation.
This commit is contained in:
Willy Tarreau 2019-03-05 12:04:55 +01:00
parent fc630bd373
commit d87a67f9bc
1 changed files with 45 additions and 1 deletions
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46
include/common/standard.h
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@ -808,7 +808,7 @@ static inline unsigned long atleast2(unsigned long a)
}
/* Simple ffs implementation. It returns the position of the lowest bit set to
* one. It is illegal to call it with a==0 (undefined result).
* one, starting at 1. It is illegal to call it with a==0 (undefined result).
*/
static inline unsigned int my_ffsl(unsigned long a)
{
@ -851,6 +851,50 @@ static inline unsigned int my_ffsl(unsigned long a)
return cnt;
}
/* Simple fls implementation. It returns the position of the highest bit set to
* one, starting at 1. It is illegal to call it with a==0 (undefined result).
*/
static inline unsigned int my_flsl(unsigned long a)
{
unsigned long cnt;
#if defined(__x86_64__)
__asm__("bsr %1,%0\n" : "=r" (cnt) : "rm" (a));
cnt++;
#else
cnt = 1;
#if LONG_MAX > 0x7FFFFFFFUL /* 64bits */
if (a & 0xFFFFFFFF00000000UL) {
a >>= 32;
cnt += 32;
}
#endif
if (a & 0XFFFF0000U) {
a >>= 16;
cnt += 16;
}
if (a & 0XFF00) {
a >>= 8;
cnt += 8;
}
if (a & 0xf0) {
a >>= 4;
cnt += 4;
}
if (a & 0xc) {
a >>= 2;
cnt += 2;
}
if (a & 0x2) {
a >>= 1;
cnt += 1;
}
#endif /* x86_64 */
return cnt;
}
/* Build a word with the <bits> lower bits set (reverse of my_popcountl) */
static inline unsigned long nbits(int bits)
{