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[/] [or1k/] [trunk/] [uclinux/] [uClinux-2.0.x/] [arch/] [alpha/] [lib/] [strlen.S] - Blame information for rev 1765

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Line No. Rev Author Line
1 199 simons
/*
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 * strlen.S (c) 1995 David Mosberger (davidm@cs.arizona.edu)
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 *
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 * Finds length of a 0-terminated string.  Optimized for the
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 * Alpha architecture:
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 *
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 *      - memory accessed as aligned quadwords only
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 *      - uses bcmpge to compare 8 bytes in parallel
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 *      - does binary search to find 0 byte in last
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 *        quadword (HAKMEM needed 12 instructions to
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 *        do this instead of the 9 instructions that
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 *        binary search needs).
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 */
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        .set noreorder
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        .set noat
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        .align 3
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        .globl  strlen
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        .ent    strlen
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strlen:
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        ldq_u   $1, 0($16)      # load first quadword ($16  may be misaligned)
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        lda     $2, -1($31)
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        insqh   $2, $16, $2
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        andnot  $16, 7, $0
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        or      $2, $1, $1
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        cmpbge  $31, $1, $2     # $2  <- bitmask: bit i == 1 <==> i-th byte == 0
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        bne     $2, found
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loop:   ldq     $1, 8($0)
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        addq    $0, 8, $0       # addr += 8
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        nop                     # helps dual issue last two insns
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        cmpbge  $31, $1, $2
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        beq     $2, loop
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found:  blbs    $2, done        # make aligned case fast
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        negq    $2, $3
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        and     $2, $3, $2
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        and     $2, 0x0f, $1
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        addq    $0, 4, $3
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        cmoveq  $1, $3, $0
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        and     $2, 0x33, $1
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        addq    $0, 2, $3
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        cmoveq  $1, $3, $0
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        and     $2, 0x55, $1
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        addq    $0, 1, $3
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        cmoveq  $1, $3, $0
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done:   subq    $0, $16, $0
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        ret     $31, ($26)
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        .end    strlen

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