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[libc] Add ffs(), ffsl(), and ffsll()

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Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2015-03-15 19:28:05 +00:00
parent 57bab4e1d3
commit 79697c75ee
4 changed files with 233 additions and 6 deletions
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38
src/arch/x86_64/include/bits/strings.h
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@@ -3,6 +3,42 @@
FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
/**
* Find first (i.e. least significant) set bit
*
* @v value Value
* @ret lsb Least significant bit set in value (LSB=1), or zero
*/
static inline __attribute__ (( always_inline )) int __ffsll ( long long value ){
long long lsb_minus_one;
/* If the input value is zero, the BSF instruction returns
* ZF=0 and leaves an undefined value in the output register.
* Perform this check in C rather than asm so that it can be
* omitted in cases where the compiler is able to prove that
* the input is non-zero.
*/
if ( value ) {
__asm__ ( "bsfq %1, %0"
: "=r" ( lsb_minus_one )
: "rm" ( value ) );
return ( lsb_minus_one + 1 );
} else {
return 0;
}
}
/**
* Find first (i.e. least significant) set bit
*
* @v value Value
* @ret lsb Least significant bit set in value (LSB=1), or zero
*/
static inline __attribute__ (( always_inline )) int __ffsl ( long value ) {
return __ffsll ( value );
}
/**
* Find last (i.e. most significant) set bit
*
@@ -13,7 +49,7 @@ static inline __attribute__ (( always_inline )) int __flsll ( long long value ){
long long msb_minus_one;
/* If the input value is zero, the BSR instruction returns
* ZF=1 and leaves an undefined value in the output register.
* ZF=0 and leaves an undefined value in the output register.
* Perform this check in C rather than asm so that it can be
* omitted in cases where the compiler is able to prove that
* the input is non-zero.