root/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 
  24 strlen:
  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 
  33 loop:   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 
  39 found:  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 
  55 done:   subq    $0, $16, $0
  56         ret     $31, ($26)
  57 
  58         .end    strlen
  59         EXPORT_SYMBOL(strlen)