Annotation of qemu/roms/qemu-palcode/strlen.S, revision 1.1

1.1     ! root        1: /*
        !             2:  * strlen.S (c) 1995 David Mosberger (davidm@cs.arizona.edu)
        !             3:  *
        !             4:  * Finds length of a 0-terminated string.  Optimized for the
        !             5:  * Alpha architecture:
        !             6:  *
        !             7:  *     - memory accessed as aligned quadwords only
        !             8:  *     - uses bcmpge to compare 8 bytes in parallel
        !             9:  *     - does binary search to find 0 byte in last
        !            10:  *       quadword (HAKMEM needed 12 instructions to
        !            11:  *       do this instead of the 9 instructions that
        !            12:  *       binary search needs).
        !            13:  */
        !            14: 
        !            15:        .set noreorder
        !            16:        .set noat
        !            17: 
        !            18:        .align 3
        !            19: 
        !            20:        .globl  strlen
        !            21:        .ent    strlen
        !            22: strlen:
        !            23:        .frame  $sp, 0, $26, 0
        !            24:        .prologue 0
        !            25: 
        !            26:        ldq_u   $1, 0($16)      # load first quadword ($16  may be misaligned)
        !            27:        lda     $2, -1($31)
        !            28:        insqh   $2, $16, $2
        !            29:        andnot  $16, 7, $0
        !            30:        or      $2, $1, $1
        !            31:        cmpbge  $31, $1, $2     # $2  <- bitmask: bit i == 1 <==> i-th byte == 0
        !            32:        bne     $2, found
        !            33: 
        !            34: loop:  ldq     $1, 8($0)
        !            35:        addq    $0, 8, $0       # addr += 8
        !            36:        nop                     # helps dual issue last two insns
        !            37:        cmpbge  $31, $1, $2
        !            38:        beq     $2, loop
        !            39: 
        !            40: found: blbs    $2, done        # make aligned case fast
        !            41:        negq    $2, $3
        !            42:        and     $2, $3, $2
        !            43: 
        !            44:        and     $2, 0x0f, $1
        !            45:        addq    $0, 4, $3
        !            46:        cmoveq  $1, $3, $0
        !            47: 
        !            48:        and     $2, 0x33, $1
        !            49:        addq    $0, 2, $3
        !            50:        cmoveq  $1, $3, $0
        !            51: 
        !            52:        and     $2, 0x55, $1
        !            53:        addq    $0, 1, $3
        !            54:        cmoveq  $1, $3, $0
        !            55: 
        !            56: done:  subq    $0, $16, $0
        !            57:        ret     $31, ($26)
        !            58: 
        !            59:        .end    strlen

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