memcpy_P 函数 AVR？答案

【问题标题】：memcpy_P function AVR?memcpy_P 函数 AVR？
【发布时间】：2013-01-16 18:45:28
【问题描述】：

void * memcpy_P(void * dest, PGM_VOID_P src, size_t n)

谁能告诉我上面的函数是在avr libc库中的什么地方实现的？

我似乎只能在几个头文件中找到函数的定义，而不是实际的实现。

我想这样做的原因是因为目前我正在 AVRAtmega128rfa1 上进行性能测试，并且我需要查看该函数的 AVR 汇编代码以及执行需要多长时间。

谢谢。

【问题讨论】：

标签： avr avr-gcc winavr

【解决方案1】：

在avr-libc-1.8.0中，函数定义在avr-libc-1.8.0/libc/pmstring/memcpy_P.S

    /* Copyright (c) 2002, 2005, 2006, 2007 Marek Michalkiewicz
   All rights reserved.

   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions are met:

   * Redistributions of source code must retain the above copyright
     notice, this list of conditions and the following disclaimer.
   * Redistributions in binary form must reproduce the above copyright
     notice, this list of conditions and the following disclaimer in
     the documentation and/or other materials provided with the
     distribution.
   * Neither the name of the copyright holders nor the names of
     contributors may be used to endorse or promote products derived
     from this software without specific prior written permission.

  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  POSSIBILITY OF SUCH DAMAGE. */

/* $Id: memcpy_P.S 2191 2010-11-05 13:45:57Z arcanum $ */

/** \file */
/** \ingroup avr_pgmspace
    \fn void *memcpy_P(void *dest, PGM_VOID_P src, size_t n)

    The memcpy_P() function is similar to memcpy(), except the src string
    resides in program space.

    \returns The memcpy_P() function returns a pointer to dest.  */


#if !defined(__AVR_TINY__)

#if !defined(__DOXYGEN__)

#include "macros.inc"

#define dest_hi r25
#define dest_lo r24
#define src_hi r23
#define src_lo r22
#define len_hi r21
#define len_lo r20

    ASSEMBLY_CLIB_SECTION
    .global _U(memcpy_P)
    .type   _U(memcpy_P), @function
_U(memcpy_P):
    X_movw  ZL, src_lo
    X_movw  XL, dest_lo
#if OPTIMIZE_SPEED
; 17 words, (14 + len * 9 - (len & 1)) cycles
    sbrs    len_lo, 0
    rjmp    .L_memcpy_P_start
    rjmp    .L_memcpy_P_odd
.L_memcpy_P_loop:
    X_lpm   r0, Z+
    st  X+, r0
.L_memcpy_P_odd:
    X_lpm   r0, Z+
    st  X+, r0
.L_memcpy_P_start:
    subi    len_lo, lo8(2)
    sbci    len_hi, hi8(2)
#else
; 12 words, (13 + len * 11) cycles
    rjmp    .L_memcpy_P_start
.L_memcpy_P_loop:
    X_lpm   r0, Z+
    st  X+, r0
.L_memcpy_P_start:
    subi    len_lo, lo8(1)
    sbci    len_hi, hi8(1)
#endif
    brcc    .L_memcpy_P_loop
; return dest (unchanged)
    ret
.L_memcpy_P_end:
    .size   _U(memcpy_P), .L_memcpy_P_end - _U(memcpy_P)

#endif /* not __DOXYGEN__ */

#endif /* !defined(__AVR_TINY__) */

【讨论】：