audk/ArmPkg/Library/BaseMemoryLibStm/Arm/CopyMem.S

#------------------------------------------------------------------------------ 
#
# CopyMem() worker for ARM
#
# This file started out as C code that did 64 bit moves if the buffer was
# 32-bit aligned, else it does a byte copy. It also does a byte copy for
# any trailing bytes. It was updated to do 32-byte copies using stm/ldm. 
#
# Copyright (c) 2008 - 2010, Apple Inc. All rights reserved.<BR>
# This program and the accompanying materials
# are licensed and made available under the terms and conditions of the BSD License
# which accompanies this distribution.  The full text of the license may be found at
# http://opensource.org/licenses/bsd-license.php
#
# THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
# WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
#
#------------------------------------------------------------------------------

/**
  Copy Length bytes from Source to Destination. Overlap is OK.

  This implementation 

  @param  Destination Target of copy
  @param  Source      Place to copy from
  @param  Length      Number of bytes to copy

  @return Destination


VOID *
EFIAPI
InternalMemCopyMem (
  OUT     VOID                      *DestinationBuffer,
  IN      CONST VOID                *SourceBuffer,
  IN      UINTN                     Length
  )
**/
.text
.align 2
GCC_ASM_EXPORT(InternalMemCopyMem)

ASM_PFX(InternalMemCopyMem):
  stmfd  sp!, {r4-r11, lr}
  // Save the input parameters in extra registers (r11 = destination, r14 = source, r12 = length)
  mov  r11, r0
  mov  r10, r0
  mov  r12, r2
  mov  r14, r1
  
memcopy_check_overlapped:
  cmp  r11, r1
  // If (dest < source)
  bcc  memcopy_check_optim_default
  // If (dest <= source). But with the previous condition ->  If (dest == source)
  bls  memcopy_end

  // If (source + length < dest)
  rsb  r3, r1, r11
  cmp  r12, r3
  bcc  memcopy_check_optim_default

  // If (length == 0)  
  cmp  r12, #0
  beq  memcopy_end
  
  b     memcopy_check_optim_overlap

memcopy_check_optim_default:
  // Check if we can use an optimized path ((length >= 32) && destination word-aligned && source word-aligned) for the memcopy (optimized path if r0 == 1)
  tst  r0, #0xF
  movne  r0, #0
  bne   memcopy_default
  tst  r1, #0xF
  movne  r3, #0
  moveq  r3, #1
  cmp  r2, #31
  movls  r0, #0
  andhi  r0, r3, #1
  b     memcopy_default
    
memcopy_check_optim_overlap:
  // r10 = dest_end, r14 = source_end
  add  r10, r11, r12
  add  r14, r12, r1

  // Are we in the optimized case ((length >= 32) && dest_end word-aligned && source_end word-aligned)
  cmp  r2, #31
  movls  r0, #0
  movhi  r0, #1
  tst  r10, #0xF
  movne  r0, #0
  tst  r14, #0xF
  movne  r0, #0
  b  memcopy_overlapped
  
memcopy_overlapped_non_optim:
  // We read 1 byte from the end of the source buffer
  sub  r3, r14, #1
  sub  r12, r12, #1
  ldrb  r3, [r3, #0]  
  sub  r2, r10, #1
  cmp  r12, #0
  // We write 1 byte at the end of the dest buffer
  sub  r10, r10, #1
  sub  r14, r14, #1
  strb  r3, [r2, #0]
  bne  memcopy_overlapped_non_optim
  b   memcopy_end

// r10 = dest_end, r14 = source_end
memcopy_overlapped:
  // Are we in the optimized case ?
  cmp  r0, #0
  beq  memcopy_overlapped_non_optim
  
  // Optimized Overlapped - Read 32 bytes
  sub  r14, r14, #32
  sub  r12, r12, #32
  cmp  r12, #31
  ldmia  r14, {r2-r9}
  
  // If length is less than 32 then disable optim
  movls  r0, #0
  
  cmp  r12, #0
  
  // Optimized Overlapped - Write 32 bytes  
  sub  r10, r10, #32
  stmia  r10, {r2-r9}
  
  // while (length != 0)
  bne  memcopy_overlapped
  b   memcopy_end
  
memcopy_default_non_optim:
  // Byte copy
  ldrb  r3, [r14], #1  
  sub  r12, r12, #1
  strb  r3, [r10], #1
  
memcopy_default:
  cmp  r12, #0
  beq  memcopy_end
  
// r10 = dest, r14 = source
memcopy_default_loop:
  cmp  r0, #0
  beq  memcopy_default_non_optim
  
  // Optimized memcopy - Read 32 Bytes
  sub  r12, r12, #32
  cmp  r12, #31
  ldmia  r14!, {r2-r9}
  
  // If length is less than 32 then disable optim
  movls  r0, #0
  
  cmp  r12, #0
  
  // Optimized memcopy - Write 32 Bytes
  stmia  r10!, {r2-r9}

  // while (length != 0)
  bne  memcopy_default_loop
  
memcopy_end:
  mov  r0, r11
  ldmfd  sp!, {r4-r11, pc}