LXR linux/arch/alpha/lib/strlen.S

   1/* SPDX-License-Identifier: GPL-2.0 */
   2/*
   3 * strlen.S (c) 1995 David Mosberger (davidm@cs.arizona.edu)
   4 *
   5 * Finds length of a 0-terminated string.  Optimized for the
   6 * Alpha architecture:
   7 *
   8 *      - memory accessed as aligned quadwords only
   9 *      - uses bcmpge to compare 8 bytes in parallel
  10 *      - does binary search to find 0 byte in last
  11 *        quadword (HAKMEM needed 12 instructions to
  12 *        do this instead of the 9 instructions that
  13 *        binary search needs).
  14 */
  15#include <asm/export.h>
  16        .set noreorder
  17        .set noat
  18
  19        .align 3
  20
  21        .globl  strlen
  22        .ent    strlen
  23
  24strlen:
  25        ldq_u   $1, 0($16)      # load first quadword ($16  may be misaligned)
  26        lda     $2, -1($31)
  27        insqh   $2, $16, $2
  28        andnot  $16, 7, $0
  29        or      $2, $1, $1
  30        cmpbge  $31, $1, $2     # $2  <- bitmask: bit i == 1 <==> i-th byte == 0
  31        bne     $2, found
  32
  33loop:   ldq     $1, 8($0)
  34        addq    $0, 8, $0       # addr += 8
  35        nop                     # helps dual issue last two insns
  36        cmpbge  $31, $1, $2
  37        beq     $2, loop
  38
  39found:  blbs    $2, done        # make aligned case fast
  40        negq    $2, $3
  41        and     $2, $3, $2
  42
  43        and     $2, 0x0f, $1
  44        addq    $0, 4, $3
  45        cmoveq  $1, $3, $0
  46
  47        and     $2, 0x33, $1
  48        addq    $0, 2, $3
  49        cmoveq  $1, $3, $0
  50
  51        and     $2, 0x55, $1
  52        addq    $0, 1, $3
  53        cmoveq  $1, $3, $0
  54
  55done:   subq    $0, $16, $0
  56        ret     $31, ($26)
  57
  58        .end    strlen
  59        EXPORT_SYMBOL(strlen)
  60