superrob1500
/
mirror-linux
mirror of https://github.com/torvalds/linux
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

s390/bitops: Slightly optimize ffs() and fls64() 

Use a simpler algorithm to calculate the result of ffs() and fls64().
This generates slightly better code and increases readability.

Kernel image size is reduced by ~3kb (gcc 15.1.0 + defconfig).

Suggested-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
pull/1354/merge
Heiko Carstens 2025-08-04 17:08:54 +02:00 committed by Alexander Gordeev
parent f9de6cdf4c
commit de88e74889
1 changed files with 2 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
arch/s390/include/asm/bitops.h
View File

@ -193,10 +193,9 @@ static inline unsigned long __ffs(unsigned long word)
*/
static inline int ffs(int word)
{
unsigned long mask = 2 * BITS_PER_LONG - 1;
unsigned int val = (unsigned int)word;
return (1 + (__flogr(-val & val) ^ (BITS_PER_LONG - 1))) & mask;
return BITS_PER_LONG - __flogr(-val & val);
}
/**
@ -223,9 +222,7 @@ static inline unsigned long __fls(unsigned long word)
*/
static inline int fls64(unsigned long word)
{
unsigned long mask = 2 * BITS_PER_LONG - 1;
return (1 + (__flogr(word) ^ (BITS_PER_LONG - 1))) & mask;
return BITS_PER_LONG - __flogr(word);
}
/**