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[libc] Add flsll()

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Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2014-04-27 16:11:44 +01:00
parent 3ffd309375
commit d36e814b8a
4 changed files with 112 additions and 7 deletions
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31
src/arch/x86/include/bits/strings.h
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@@ -1,31 +0,0 @@
#ifndef _BITS_STRINGS_H
#define _BITS_STRINGS_H
FILE_LICENCE ( GPL2_OR_LATER );
/**
* Find last (i.e. most significant) set bit
*
* @v value Value
* @ret msb Most significant bit set in value (LSB=1), or zero
*/
static inline __attribute__ (( always_inline )) int __flsl ( long value ) {
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.
* 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__ ( "bsr %1, %0"
: "=r" ( msb_minus_one )
: "rm" ( value ) );
return ( msb_minus_one + 1 );
} else {
return 0;
}
}
#endif /* _BITS_STRINGS_H */