Michael Brown
32 lines
783 B
C
32 lines
783 B
C
#ifndef _BITS_STRINGS_H
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#define _BITS_STRINGS_H
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FILE_LICENCE ( GPL2_OR_LATER );
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/**
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* Find last (i.e. most significant) set bit
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*
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* @v value Value
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* @ret msb Most significant bit set in value (LSB=1), or zero
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*/
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static inline __attribute__ (( always_inline )) int __flsl ( long value ) {
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long msb_minus_one;
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/* If the input value is zero, the BSR instruction returns
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* ZF=1 and leaves an undefined value in the output register.
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* Perform this check in C rather than asm so that it can be
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* omitted in cases where the compiler is able to prove that
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* the input is non-zero.
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*/
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if ( value ) {
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__asm__ ( "bsr %1, %0"
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: "=r" ( msb_minus_one )
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: "rm" ( value ) );
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return ( msb_minus_one + 1 );
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} else {
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return 0;
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}
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}
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#endif /* _BITS_STRINGS_H */
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