Subversion Repositories or1k

/*
 * 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