strlen_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
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  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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/* $Id$ */

/** \file */
/** \ingroup avr_pgmspace
    \fn size_t strlen_P(PGM_P src)

    The strlen_P() function is similar to strlen(), except that src is a
    pointer to a string in program space.

    \returns The strlen() function returns the number of characters in src.
    
    \note strlen_P() is implemented as an inline function in the avr/pgmspace.h
    header file, which will check if the length of the string is a constant
    and known at compile time. If it is not known at compile time, the macro
    will issue a call to __strlen_P() which will then calculate the length
    of the string as normal.
*/

#if !defined(__AVR_TINY__)

#if !defined(__DOXYGEN__)

#include "macros.inc"

#define src_hi r25
#define src_lo r24

; 11 words, (14 + __strlen_P(src) * 8) cycles

        ASSEMBLY_CLIB_SECTION
        .global _U(__strlen_P)
        .type   _U(__strlen_P), @function
_U(__strlen_P):
        X_movw  ZL, src_lo
.L_strlen_P_loop:
        X_lpm   r0, Z+
        tst     r0
        brne    .L_strlen_P_loop
; return Z - 1 - src = (-1 - src) + Z = ~src + Z
        com     src_lo
        com     src_hi
        add     src_lo, ZL
        adc     src_hi, ZH
        ret
.L_strlen_P_end:
        .size   _U(__strlen_P), .L_strlen_P_end - _U(__strlen_P)

#endif /* not __DOXYGEN__ */

#endif /* !defined(__AVR_TINY__) */