source: trunk/libs/newlib/src/newlib/libc/machine/i960/strrchr.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 "strrchr.s"
#ifdef  __i960_BIG_ENDIAN__
#error  "This does not work in big-endian"
#endif

#ifdef  __PIC
        .pic
#endif
#ifdef  __PID
        .pid
#endif

/*
 * (c) copyright 1988,1993 Intel Corp., all rights reserved
 */

/*
        procedure strrchr  (optimized assembler version for the 80960K series)

        src_addr = strrchr (src_addr, char)

        return a pointer to the last byte that contains the indicated
        byte in the source string.  Return null if the byte is not found.

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

        Strategy:

        Fetch the source string by words and scanbyte the words for the 
        char until either a word with the byte is found or the null byte is
        encountered.  In the former case, move through the word to find the
        matching byte and save its memory address, then continue the search.  
        In the latter case, return the saved address, or zero (null) if none
        was ever found to save.

        Tactics:

        1) Do NOT try to fetch the words in a word aligned manner because,
        in my judgement, the performance degradation experienced due to 
        non-aligned accesses does NOT outweigh the time and complexity added 
        by the preamble that would be necessary to assure alignment.  This 
        is supported by the intuition that most source arrays (even more 
        true of most big source arrays) will be word aligned to begin with.
*/

        .globl  _strrchr
        .globl  __strrchr
        .leafproc       _strrchr, __strrchr
        .align  2
_strrchr:
#ifdef __PIC
        lda     Lrett-(.+8)(ip),g14
#else
        lda     Lrett,g14
#endif
__strrchr:

        ld      (g0),g4         # fetch first word
        lda     0xff,g7         # byte extraction mask
        and     g1,g7,g1        # make char an 8-bit ordinal
        shlo    8,g1,g2         # broadcast the char to four bytes
        or      g1,g2,g2
        shlo    16,g2,g5
        or      g2,g5,g3
        mov     g14,g13         # preserve return address
        addo    4,g0,g2         # post-increment src pointer
        mov     1,g0            # prepare to return null pointer
        mov     g3,g6           # prepare to return null pointer

Lsearch_for_word_with_char_or_null:
        mov     g4,g5           # copy word
        scanbyte 0,g5           # check for null byte
        ld      (g2),g4         # fetch next word of src
        bo      Lword_has_null  # branch if null found 
        scanbyte g3,g5          # check for byte with char
        addo    4,g2,g2         # post-increment src pointer
        bno     Lsearch_for_word_with_char_or_null   # branch if no copy of char
        mov     g5,g6           # save word that has char in it (at least once)
        subo    4,g2,g0         # save addr of byte after word with char
        b       Lsearch_for_word_with_char_or_null

Lword_has_null:
        subo    4,g2,g2         # move src pointer back to word with null
Lfind_null:
        addo    1,g2,g2         # advance src pointer to byte after current
        and     g7,g5,g14       # extract next byte
        cmpo    g1,g14          # is current byte char?
        shro    8,g5,g5         # position next byte for extraction
        bne     1f              # skip if not char sought after
        mov     g2,g0           # save addr of byte after char
        mov     g3,g6           # save word of all char to short circuit search
1:      cmpobne 0,g14,Lfind_null        # is current byte null?

Lfind_last_char:
        rotate  8,g6,g6         # position next highest byte
        and     g7,g6,g5        # extract byte
        subo    1,g0,g0         # move pointer to that byte (or nullify)
        cmpobne g5,g1,Lfind_last_char   # branch if not at char

        bx      (g13)           # g0 = addr of char in src (or null);  g14 = 0
Lrett:
        ret

/* end of strrchr */