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/*

 * strlen.S (c) 1995 David Mosberger (davidm@cs.arizona.edu)

 *

 * Finds length of a 0-terminated string.  Optimized for the

 * Alpha architecture:

 *

 *      - memory accessed as aligned quadwords only

 *      - uses bcmpge to compare 8 bytes in parallel

 *      - does binary search to find 0 byte in last

 *        quadword (HAKMEM needed 12 instructions to

 *        do this instead of the 9 instructions that

 *        binary search needs).

 */

        .set noreorder

        .set noat

        .align 3

        .globl  strlen

        .ent    strlen

strlen:

        ldq_u   $1, 0($16)      # load first quadword ($16  may be misaligned)

        lda     $2, -1($31)

        insqh   $2, $16, $2

        andnot  $16, 7, $0

        or      $2, $1, $1

        cmpbge  $31, $1, $2     # $2  <- bitmask: bit i == 1 <==> i-th byte == 0

        bne     $2, found

loop:   ldq     $1, 8($0)

        addq    $0, 8, $0       # addr += 8

        nop                     # helps dual issue last two insns

        cmpbge  $31, $1, $2

        beq     $2, loop

found:  blbs    $2, done        # make aligned case fast

        negq    $2, $3

        and     $2, $3, $2

        and     $2, 0x0f, $1

        addq    $0, 4, $3

        cmoveq  $1, $3, $0

        and     $2, 0x33, $1

        addq    $0, 2, $3

        cmoveq  $1, $3, $0

        and     $2, 0x55, $1

        addq    $0, 1, $3

        cmoveq  $1, $3, $0

done:   subq    $0, $16, $0

        ret     $31, ($26)

        .end    strlen