source: trunk/libs/newlib/src/newlib/libc/machine/i960/strlen_ca.S @ 444

/*******************************************************************************
 * 
 * Copyright (c) 1993 Intel Corporation
 * 
 * Intel hereby grants you permission to copy, modify, and distribute this
 * software and its documentation.  Intel grants this permission provided
 * that the above copyright notice appears in all copies and that both the
 * copyright notice and this permission notice appear in supporting
 * documentation.  In addition, Intel grants this permission provided that
 * you prominently mark as "not part of the original" any modifications
 * made to this software or documentation, and that the name of Intel
 * Corporation not be used in advertising or publicity pertaining to
 * distribution of the software or the documentation without specific,
 * written prior permission.
 * 
 * Intel Corporation provides this AS IS, WITHOUT ANY WARRANTY, EXPRESS OR
 * IMPLIED, INCLUDING, WITHOUT LIMITATION, ANY WARRANTY OF MERCHANTABILITY
 * OR FITNESS FOR A PARTICULAR PURPOSE.  Intel makes no guarantee or
 * representations regarding the use of, or the results of the use of,
 * the software and documentation in terms of correctness, accuracy,
 * reliability, currentness, or otherwise; and you rely on the software,
 * documentation and results solely at your own risk.
 *
 * IN NO EVENT SHALL INTEL BE LIABLE FOR ANY LOSS OF USE, LOSS OF BUSINESS,
 * LOSS OF PROFITS, INDIRECT, INCIDENTAL, SPECIAL OR CONSEQUENTIAL DAMAGES
 * OF ANY KIND.  IN NO EVENT SHALL INTEL'S TOTAL LIABILITY EXCEED THE SUM
 * PAID TO INTEL FOR THE PRODUCT LICENSED HEREUNDER.
 * 
 ******************************************************************************/

        .file "strle_ca.s"
#ifdef  __PIC
        .pic
#endif
#ifdef  __PID
        .pid
#endif
/*
 * (c) copyright 1988,1993 Intel Corp., all rights reserved
 */

/*
        procedure strlen  (optimized assembler version for the CA)

        src_addr = strlen (src_addr)

        return the number of bytes that precede the null byte in the
        string pointed to by src_addr.

        Undefined behavior will occur if the end of the source string (i.e. 
        the terminating null byte) is in the last four words of the program's
        allocated memory space.  This is so because, in several cases, strlen
        will fetch ahead several words.  Disallowing the fetch ahead would 
        impose a severe performance penalty.

        This program handles two cases:

        1) the argument starts on a word boundary
        2) the argument doesn't start on a word boundary

        At the time of this writing, only g0 thru g7 and g13 are available 
        for use in this leafproc;  other registers would have to be saved and
        restored.  These nine registers, plus tricky use of g14 are sufficient
        to implement the routine.  The registers are used as follows:

        g0  original src ptr;  upon return it is the byte count.
        g1
        g2  src ptr  
        g3  mask
        g4  even word of the source string
        g5  odd word of the source string
        g6  copy of even word, shift count
        g7  copy of odd word
        g13 return address
        g14 byte extracted.
*/

        .globl  _strlen
        .globl  __strlen
        .leafproc       _strlen, __strlen
        .align  2
_strlen:
#ifndef __PIC
        lda     Lrett,g14
#else
        lda     Lrett-(.+8)(ip),g14
#endif
__strlen:

        notand  g0,3,g2         # extract word addr of start of src
        lda     (g14),g13       # preserve return address
        and     g0,3,g7         # extract byte offset of src
        ld      (g2),g5         # fetch word containing at least first byte
        shlo    3,g7,g7         # get shift count for making mask for first word
        lda     4(g2),g2        # post-increment src word pointer
        subi    1,0,g3          # mask initially all ones
        chkbit  2,g2            # are we on an even word boundary or an odd one?
#if __i960_BIG_ENDIAN__
        shro    g7,g3,g3        # get mask for bytes needed from first word
        notor   g5,g3,g7        # set unneeded bytes to all ones
        lda     0xff000000,g3   # byte extraction mask
#else
        shlo    g7,g3,g3        # get mask for bytes needed from first word
        notor   g5,g3,g7        # set unneeded bytes to all ones
        lda     0xff,g3         # byte extraction mask
#endif
        bno.f   Lodd_word       # branch if first word is odd
        mov     g7,g4           # move first word to copy thereof
        ld      (g2),g5         # load odd word
        lda     4(g2),g2        # post-increment src word pointer
        

Leven_word:
        scanbyte 0,g4           # check for null byte
        movl    g4,g6           # copy both words
Lodd_word:                      # trickery!  if we branch here, following branch
                                /* instruction will fall thru, as we want,  */
                                /* effecting the load of g4 and g5 only. */
        ldl     (g2),g4         # fetch next pair of word of src
        bo.f    Lsearch_for_null        # branch if null found 
        scanbyte 0,g7           # check for null byte
        lda     8(g2),g2        # post-increment src word pointer
        bno.t   Leven_word      # branch if null not found yet

        subo    4,g2,g2         # back up the byte pointer
        lda     (g7),g6         # move odd word to search word
Lsearch_for_null:
        subo    9,g2,g2         # back up the byte pointer
Lsearch_for_null.a:
        and     g6,g3,g14       # extract byte
        cmpo    0,g14           # is it null?
        lda     1(g2),g2        # bump src byte ptr
#if __i960_BIG_ENDIAN__
        shlo    8,g6,g6         # shift word to position next byte
#else
        shro    8,g6,g6         # shift word to position next byte
#endif
        bne.t   Lsearch_for_null.a

Lexit_code:
        subo    g0,g2,g0        # calculate string length
        bx      (g13)           # g0 = addr of src;  g14 = 0
Lrett:
        ret

/* end of strlen */