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

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

        dest_addr = strncpy (dest_addr, src_addr, max_bytes)

        copy the null terminated string pointed to by src_addr to 
        the string space pointed to by dest_addr.  Return the original
        dest_addr.  If the source string is shorter than max_bytes,
        then null-pad the destination string.

        This routine will fail if the source and destination string
        overlap (in particular, if the end of the source is overlapped
        by the beginning of the destination).  The behavior is undefined.
        This is acceptable according to the draft C standard.

        Undefined behavior will also occur if the end of the 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, strcpy
        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) source is word aligned, destination is not
        4) destination is word aligned, source 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 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 dest ptr;  not modified, so that it may be returned.
        g1  src ptr;  shift count
        g2  max_bytes
        g3  src ptr (word aligned)
        g4  dest ptr (word aligned)
        g5  0xff  --  byte extraction mask
        Little endian:
                g6  lsw of double word for extraction of 4 bytes
                g7  msw of double word for extraction of 4 bytes
        Big endian:
                g6  msw of double word for extraction of 4 bytes
                g7  lsw of double word for extraction of 4 bytes
        g13 return address
        g14 byte extracted.
*/

#if __i960_BIG_ENDIAN__
#define MSW g6
#define LSW g7
#else
#define LSW g6
#define MSW g7
#endif

        .globl  _strncpy
        .globl  __strncpy
        .leafproc       _strncpy, __strncpy
        .align  2
_strncpy:
#ifndef __PIC
        lda     Lrett,g14
#else
        lda     Lrett-(.+8)(ip),g14
#endif
__strncpy:
        notand  g1,3,g3         # extract word addr of start of src
         lda    (g14),g13       # preserve return address
         cmpibge.f 0,g2,Lexit_code # Lexit if number of bytes to move is <= zero.
        cmpo    g3,g1           # check alignment of src
         ld     (g3),LSW        # fetch word containing at least first byte
        notand  g0,3,g4         # extract word addr of start of dest
         lda    4(g3),g3        # advance src word addr
         bne.f  Lcase_245       # branch if src is NOT word aligned

Lcase_13:
        cmpo    g0,g4           # check alignment of dest
         lda    0xff,g5         # load mask for byte extraction
        subo    4,g4,g4         # store is pre-incrementing;  back up dest addr
         bne.f  Lcase_3         # branch if dest not word aligned

Lcase_1:                                # src and dest are word aligned
Lcase_1_wloop:                  # word copying loop
        cmpi    g2,4            # check for fewer than four bytes to move
         lda    (LSW),g1        # keep a copy of the src word
        addo    4,g4,g4         # pre-increment dest addr
         bl.f   Lcase_1_cloop.a # branch if fewer than four bytes to copy
        scanbyte 0,g1           # check for null byte in src word
         ld     (g3),LSW        # pre-fetch next word of src
        subi    4,g2,g2         # decrease max_byte count by the 4 bytes moved
         bo.f   Lcase_1_cloop.c # branch if word contains null byte
        addo    4,g3,g3         # post-increment src addr
         st     g1,(g4)         # store word in dest string
         b      Lcase_1_wloop

Lcase_3_cloop.a:
Lcase_1_cloop.a:                        # character copying loop (max_bytes <= 3)
#if __i960_BIG_ENDIAN__
        rotate  8,g1,g1         # move next byte into position for extraction
#endif
        and     g5,g1,g14       # extract next char
Lcase_1_cloop.b:
        cmpdeci 0,g2,g2         # is max_bytes exhausted?
        be.f    Lexit_code      # Lexit if max_bytes is exhausted
        cmpo    0,g14           # check for null byte
         stob   g14,(g4)        # store the byte in dest
#if ! __i960_BIG_ENDIAN__
        shro    8,g1,g1         # move next byte into position for extraction
#endif
         lda    1(g4),g4        # post-increment dest byte addr
         bne.t  Lcase_1_cloop.a # branch if null not reached
         b      Lcase_1_cloop.b

Lexit_code:
        mov     0,g14           # conform to register conventions
        bx      (g13)           # g0 = addr of dest;  g14 = 0
Lrett:
        ret

Lcase_1_cloop.c:
Lcase_3_cloop.c:
#if __i960_BIG_ENDIAN__
        rotate  24,g5,g5        # move mask into position for testing next byte
#endif
        and     g5,g1,g14       # extract next char
        cmpo    0,g14           # check for null byte
#if ! __i960_BIG_ENDIAN__
         lda    (g5),LSW        # keep a copy of the current mask
        shlo    8,g5,g5         # move mask into position for testing next byte
#endif
         bne.t  Lcase_1_cloop.c # branch if null not reached
#if __i960_BIG_ENDIAN__
        subo    1,g5,g5         # null pad.
        andnot  g5,g1,g1        # last bytes to copy, and null pad rest of word
#else
        subo    1,LSW,g5        # mask to get last bytes to copy, and null pad
        and     g5,g1,g1        # last bytes to copy, and null pad rest of word
#endif
        st      g1,(g4) 

Lcase_1_zwloop:                 # zero word loop
        cmpi    g2,4            # check for fewer than four bytes to move
        addo    4,g4,g4         # pre-increment dest addr
         bl.f   Lcase_1_cloop.b # branch if fewer than four bytes to copy
        subo    4,g2,g2         # decrease max_byte count by the 4 bytes moved
         st     g14,(g4)        # store word in dest string
         b      Lcase_1_zwloop

Lcase_3:                                # src is word aligned; dest is not
        addo    8,g4,g4         # move dest word ptr to first word boundary
         lda    (g0),g1         # copy dest byte ptr
        mov     LSW,MSW         # make copy of first word of src
         lda    32,g14          # initialize shift count to zero (mod 32)

Lcase_25:
Lcase_3_cloop_at_start:         # character copying loop for start of dest str
        cmpdeci 0,g2,g2         # is max_bytes exhausted?
#if __i960_BIG_ENDIAN__
        shro    24,MSW,g5       # extract next char
#else
        and     g5,MSW,g5       # extract next char
#endif
         be.f   Lexit_code      # Lexit if max_bytes is exhausted
        cmpo    0,g5            # check for null byte
         stob   g5,(g1)         # store the byte in dest
        addo    1,g1,g1         # post-increment dest ptr
         lda    0xff,g5         # re-initialize byte extraction mask
         bne.t  1f              # drop thru if null byte reached (to pad)
        movl    0,g6            # blank out remainder of input buffer
1:
        cmpo    g1,g4           # have we reached word boundary in dest yet?
#if __i960_BIG_ENDIAN__
         lda    -8(g14),g14     # augment the shift counter
        rotate  8,MSW,MSW       # move next byte into position for extraction
#else
         lda    8(g14),g14      # augment the shift counter
        shro    8,MSW,MSW       # move next byte into position for extraction
#endif
         bne.t  Lcase_3_cloop_at_start  # branch if reached word boundary?

        ld      (g3),MSW        # fetch msw of operand for double shift

Lcase_4:

#if __i960_BIG_ENDIAN__
        cmpobne 0,g14,Lcase_3_wloop # branch if src is still unaligned.

Lcase_3_wloop2:
        cmpi    g2,4            # less than four bytes to move?
         lda    (LSW),g1        # extract 4 bytes of src
        lda     4(g3),g3        # post-increment src word addr
         bl.f   Lcase_3_cloop.a # branch if < four bytes left to move
        scanbyte 0,g1           # check for null byte
         lda    (MSW),LSW       # move msw to lsw
        subi    4,g2,g2         # decrease max_byte count by the 4 bytes moved
         ld     (g3),MSW        # pre-fetch msw of operand for double shift
         bo.f   Lcase_3_cloop.c # branch if word contains null byte
        st      g1,(g4)         # store 4 bytes to dest
        addo    4,g4,g4         # post-increment dest ptr
         b      Lcase_3_wloop2

#endif

Lcase_3_wloop:
        cmpi    g2,4            # less than four bytes to move?
        eshro   g14,g6,g1       # extract 4 bytes of src
         lda    4(g3),g3        # post-increment src word addr
         bl.f   Lcase_3_cloop.a # branch if < four bytes left to move
        scanbyte 0,g1           # check for null byte
         lda    (MSW),LSW       # move msw to lsw
        subi    4,g2,g2         # decrease max_byte count by the 4 bytes moved
         ld     (g3),MSW        # pre-fetch msw of operand for double shift
         bo.f   Lcase_3_cloop.c # branch if word contains null byte
        st      g1,(g4)         # store 4 bytes to dest
        addo    4,g4,g4         # post-increment dest ptr
         b      Lcase_3_wloop

Lcase_245:
        cmpo    g0,g4           # check alignment of dest
         ld     (g3),MSW        # pre-fetch second half
        and     3,g1,g1         # compute shift count
         lda    0xff,g5         # load mask for byte extraction
#if __i960_BIG_ENDIAN__
        subo    g1,4,g14        # adjust shift count for big endian.
        shlo    3,g14,g14       
#else
        shlo    3,g1,g14        
#endif
         be.t   Lcase_4         # branch if dest is word aligned
        or      g4,g1,g1        # is src earlier in word, later, or sync w/ dst
        cmpo    g0,g1           # < indicates first word of dest has more bytes
                                /* than first word of source. */
         lda    4(g4),g4        # move dest word addr to first word boundary
        eshro   g14,g6,g5       # extract four bytes
         lda    (g0),g1
         bg.f   1f
        mov     MSW,LSW
         lda    4(g3),g3        # move src word addr to second word boundary
1:
        mov     g5,MSW
         lda    0xff,g5
         b      Lcase_25

/* end of strncpy */