source: trunk/libs/newlib/src/newlib/libc/machine/i960/strncmp_ca.S @ 690

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

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

        result = strncmp (src1_addr, src2_addr, max_bytes)

        compare the null terminated string pointed to by src1_addr to 
        the string space pointed to by src2_addr.  Return 0 iff the strings
        are equal, -1 if src1_addr is lexicly less than src2_addr, and 1
        if it is lexicly greater.  Do not compare more than max_bytes bytes.

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

        This program handles five cases:

        1) both arguments start on a word boundary
        2) neither are word aligned, but they are offset by the same amount
        3) source1 is word aligned, source2 is not
        4) source2 is word aligned, source1 is not
        5) neither is word aligned, and they are offset by differing amounts

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

        g0  original src1 ptr;  extracted word;  return result
        g1  src2 ptr;  0xff  --  byte extraction mask
        g2  maximum number of bytes to compare
        g3  src2 word ptr 
        Little endian:
                g4  lsw of src1
                g5  msw of src1
                g6  src2 word
                g7  src1 word ptr
        Big endian:
                g4  msw of src1
                g5  lsw of src1
                g6  src1 word ptr
                g7  src2 word
        g13 return address
        g14 shift count
*/

#if __i960_BIG_ENDIAN__
#define MSW g4
#define LSW g5
#define SRC1 g6
#define SRC2 g7
#else
#define LSW g4
#define MSW g5
#define SRC2 g6
#define SRC1 g7
#endif

        .globl  _strncmp
        .globl  __strncmp
        .leafproc       _strncmp, __strncmp
        .align  2
_strncmp:
#ifndef __PIC
        lda     Lrett,g14
#else
        lda     Lrett-(.+8)(ip),g14
#endif
__strncmp:
Lrestart:
        notand  g0,3,SRC1       # extract word addr of start of src1
         lda    (g14),g13       # preserve return address
         cmpibge.f 0,g2,Lequal_exit     # return equality if number of bytes to
                                        /* compare is none. */
#if __i960_BIG_ENDIAN__
        cmpo    g0,SRC1         # check alignment of src1
#endif
         ld     (SRC1),LSW      # fetch word with at least first byte of src1
        notand  g1,3,g3         # extract word addr of start of src2
         ld     4(SRC1),MSW     # fetch second word of src1
#if __i960_BIG_ENDIAN__
         bne    Lsrc1_unaligned # branch if src1 is unaligned
        cmpo    g3,g1           # check alignment of src2
         ld     (g3),SRC2       # fetch word with at least first byte of src2
        shlo    3,g0,g14        # compute shift count for src1
        subo    g14,0,g14       # adjust shift count for big endian
         lda    8(SRC1),SRC1    # advance src1 word addr
         bne.f  Lsrc2_unaligned # branch if src2 is NOT word aligned

                                /* src2 is word aligned */

        mov     LSW,g0

Lwloop2:                                # word comparing loop
        cmpo    SRC2,g0         # compare src1 and src2 words
         lda    0xff000000,g1   # byte extraction mask
        mov     MSW,LSW         # move msw of src1 to lsw
         ld     (SRC1),MSW      # pre-fetch next msw of src1
        addo    4,SRC1,SRC1     # post-increment src1 addr
         lda    4(g3),g3        # pre-increment src2 addr
         bne.f  Lcloop          # branch if src1 and src2 unequal
        scanbyte 0,g0           # check for null byte in src1 word
         ld     (g3),SRC2       # pre-fetch next word of src2
        mov     LSW,g0          # extract word of src1
         subi   4,g2,g2         # decrement maximum byte count
        bo.f    Lequal_exit     # branch if null byte encountered
        cmpibl.t 0,g2,Lwloop2   # branch if max_bytes not reached yet

        b       Lequal_exit     # strings were equal up through max_bytes

Lsrc1_unaligned:
#endif
        cmpo    g3,g1           # check alignment of src2
         ld     (g3),SRC2       # fetch word with at least first byte of src2
        shlo    3,g0,g14        # compute shift count for src1
#if __i960_BIG_ENDIAN__
        subo    g14,0,g14       # adjust shift count for big endian
#endif
        eshro   g14,g4,LSW      # extract word of src1
         lda    8(SRC1),SRC1    # advance src1 word addr
         bne.f  Lsrc2_unaligned # branch if src2 is NOT word aligned

                                /* at least src2 is word aligned */

        mov     LSW,g0

Lwloop:                         # word comparing loop
        cmpo    SRC2,g0         # compare src1 and src2 words
#if __i960_BIG_ENDIAN__
         lda    0xff000000,g1   # byte extraction mask
#else
         lda    0xff,g1         # byte extraction mask
#endif
        mov     MSW,LSW         # move msw of src1 to lsw
         ld     (SRC1),MSW      # pre-fetch next msw of src1
        addo    4,SRC1,SRC1     # post-increment src1 addr
         lda    4(g3),g3        # pre-increment src2 addr
         bne.f  Lcloop          # branch if src1 and src2 unequal
        scanbyte 0,g0           # check for null byte in src1 word
         ld     (g3),SRC2       # pre-fetch next word of src2
        eshro   g14,g4,g0       # extract word of src1
         subi   4,g2,g2         # decrement maximum byte count
        bo.f    Lequal_exit     # branch if null byte encountered
        cmpibl.t 0,g2,Lwloop    # branch if max_bytes not reached yet

        b       Lequal_exit     # strings were equal up through max_bytes

Lcloop_setup:                   # setup for coming from Lsrc2_unaligned
        mov     LSW,g0          # restore extracted src1 word
#if __i960_BIG_ENDIAN__
         lda    0xff000000,g1   # byte extraction mask
#else
         lda    0xff,g1         # byte extraction mask
#endif

Lcloop:                         # character comparing loop
        and     SRC2,g1,g3      # extract next char of src2
        and     g0,g1,LSW       # extract next char of src1
        cmpobne.f LSW,g3,.diff  # check for equality
        cmpo    0,LSW           # check for null byte
#if __i960_BIG_ENDIAN__
        shro    8,g1,g1         # shift mask for next byte
#else
        shlo    8,g1,g1         # shift mask for next byte
#endif
        subi    1,g2,g2         # decrement character counter
         bne.t  Lcloop          # branch if null not reached

                                /* words are equal up thru null byte */

Lequal_exit:
        mov     0,g14           # conform to register conventions
         lda    0,g0            # return zero, indicating equality
        bx      (g13)           # return

Lrett:
        ret

.diff:
        mov     0,g14
         bl     Lless_than_exit
Lgreater_than_exit:
        cmpibge.f 0,g2,Lequal_exit  # branch if difference is beyond max_bytes
        mov     1,g0
         bx     (g13)           # g0 = 1 (src1 > src2)
Lless_than_exit:
        cmpibge.f 0,g2,Lequal_exit  # branch if difference is beyond max_bytes
        subi    1,0,g0
         bx     (g13)           # g0 = -1 (src1 < src2)

Lsrc2_unaligned:
        notor   g1,3,g14        # first step in computing new src1 ptr
         ld     4(g3),SRC1      # fetch second word of src2
        shlo    3,g1,MSW        # compute shift count for src2
#if __i960_BIG_ENDIAN__
        subo    MSW,0,MSW       # adjust shift count for big endian
#endif
        eshro   MSW,g6,SRC2     # extract word of src2
        cmpo    LSW,SRC2        # compare src1 and src2 words
         lda    4(g3),g1        # set new src2 ptr
         bne.f  Lcloop_setup    # first four bytes differ
        scanbyte 0,LSW          # check for null byte
        subo    g14,g0,g0       # second (final) step in computing new src1 ptr
        addi    g14,g2,g2       # compute new max_bytes too
         lda    (g13),g14       # prepare return pointer for Lrestart
         bno.t  Lrestart                # if null byte not encountered, continue 
                                /* with both string fetches shifted such that*/
                                /* src2 is now word aligned.*/
        mov     0,g14           # conform to register conventions.
         lda    0,g0            # return indicator of equality.
        bx      (g13)