root/arch/nds32/lib/memmove.S

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   1 // SPDX-License-Identifier: GPL-2.0
   2 // Copyright (C) 2005-2017 Andes Technology Corporation
   3 
   4 #include <linux/linkage.h>
   5 
   6 /*
   7   void *memmove(void *dst, const void *src, int n);
   8 
   9   dst: $r0
  10   src: $r1
  11   n  : $r2
  12   ret: $r0 - pointer to the memory area dst.
  13 */
  14         .text
  15 
  16 ENTRY(memmove)
  17         move    $r5, $r0                ! Set return value = det
  18         beq     $r0, $r1, exit_memcpy   ! Exit when det = src
  19         beqz    $r2, exit_memcpy        ! Exit when n = 0
  20         pushm   $t0, $t1                ! Save reg
  21         srli    $p1, $r2, #2            ! $p1 is how many words to copy
  22 
  23         ! Avoid data lost when memory overlap
  24         ! Copy data reversely when src < dst
  25         slt     $p0, $r0, $r1           ! check if $r0 < $r1
  26         beqz    $p0, do_reverse         ! branch if dst > src
  27 
  28         ! No reverse, dst < src
  29         andi    $r2, $r2, #3            ! How many bytes are less than a word
  30         li      $t0, #1                 ! Determining copy direction in byte_cpy
  31         beqz    $p1, byte_cpy           ! When n is less than a word
  32 
  33 word_cpy:
  34         lmw.bim $p0, [$r1], $p0         ! Read a word from src
  35         addi    $p1, $p1, #-1           ! How many words left to copy
  36         smw.bim $p0, [$r0], $p0         ! Copy the word to det
  37         bnez    $p1, word_cpy           ! If remained words > 0
  38         beqz    $r2, end_memcpy         ! No left bytes to copy
  39         b       byte_cpy
  40 
  41 do_reverse:
  42         add     $r0, $r0, $r2           ! Start with the end of $r0
  43         add     $r1, $r1, $r2           ! Start with the end of $r1
  44         andi    $r2, $r2, #3            ! How many bytes are less than a word
  45         li      $t0, #-1                ! Determining copy direction in byte_cpy
  46         beqz    $p1, reverse_byte_cpy   ! When n is less than a word
  47 
  48 reverse_word_cpy:
  49         lmw.adm $p0, [$r1], $p0         ! Read a word from src
  50         addi    $p1, $p1, #-1           ! How many words left to copy
  51         smw.adm $p0, [$r0], $p0         ! Copy the word to det
  52         bnez    $p1, reverse_word_cpy   ! If remained words > 0
  53         beqz    $r2, end_memcpy         ! No left bytes to copy
  54 
  55 reverse_byte_cpy:
  56         addi    $r0, $r0, #-1
  57         addi    $r1, $r1, #-1
  58 byte_cpy:                               ! Less than 4 bytes to copy now
  59         lb.bi   $p0, [$r1], $t0         ! Read a byte from src
  60         addi    $r2, $r2, #-1           ! How many bytes left to copy
  61         sb.bi   $p0, [$r0], $t0         ! copy the byte to det
  62         bnez    $r2, byte_cpy           ! If remained bytes > 0
  63 
  64 end_memcpy:
  65         popm    $t0, $t1
  66 exit_memcpy:
  67         move    $r0, $r5
  68         ret
  69 
  70 ENDPROC(memmove)

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