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/*
 * arch/alpha/lib/ev67-strlen.S
 * 21264 version by Rick Gorton <rick.gorton@alpha-processor.com>
 *
 * 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