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/*

 * arch/alpha/lib/ev67-strlen.S

 * 21264 version by Rick Gorton 

 *

 * 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

 *

 * Much of the information about 21264 scheduling/coding comes from:

 *      Compiler Writer's Guide for the Alpha 21264

 *      abbreviated as 'CWG' in other comments here

 *      ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html

 * Scheduling notation:

 *      E       - either cluster

 *      U       - upper subcluster; U0 - subcluster U0; U1 - subcluster U1

 *      L       - lower subcluster; L0 - subcluster L0; L1 - subcluster L1

 */

        .set noreorder

        .set noat

        .globl  strlen

        .ent    strlen

        .align 4

strlen:

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

        lda     $2, -1($31)     # E :

        insqh   $2, $16, $2     # U :

        andnot  $16, 7, $0      # E :

        or      $2, $1, $1      # E :

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

        nop                     # E :

        bne     $2, $found      # U :

$loop:  ldq     $1, 8($0)       # L :

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

        cmpbge  $31, $1, $2     # E :

        beq     $2, $loop       # U :

$found:

        cttz    $2, $3          # U0 :

        addq    $0, $3, $0      # E :

        subq    $0, $16, $0     # E :

        ret     $31, ($26)      # L0 :

        .end    strlen