strings.h

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#ifndef _BITS_STRINGS_H
#define _BITS_STRINGS_H
 
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 __ffsl ( long value ) {
        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__ ( "bsfl %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 __ffsll ( long long value ){
        unsigned long high = ( value >> 32 );
        unsigned long low = ( value >> 0 );
 
        if ( low ) {
                return ( __ffsl ( low ) );
        } else if ( high ) {
                return ( 32 + __ffsl ( high ) );
        } else {
                return 0;
        }
}
 
/**
 * 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=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__ ( "bsrl %1, %0"
                          : "=r" ( msb_minus_one )
                          : "rm" ( value ) );
                return ( msb_minus_one + 1 );
        } else {
                return 0;
        }
}
 
/**
 * 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 __flsll ( long long value ){
        unsigned long high = ( value >> 32 );
        unsigned long low = ( value >> 0 );
 
        if ( high ) {
                return ( 32 + __flsl ( high ) );
        } else if ( low ) {
                return ( __flsl ( low ) );
        } else {
                return 0;
        }
}
 
#endif /* _BITS_STRINGS_H */