source: trunk/libs/newlib/src/newlib/libc/machine/arc/strcmp.S @ 444

/*
   Copyright (c) 2015, Synopsys, Inc. All rights reserved.

   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions are met:

   1) Redistributions of source code must retain the above copyright notice,
   this list of conditions and the following disclaimer.

   2) 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.

   3) Neither the name of the Synopsys, Inc., nor the names of its 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 HOLDER OR CONTRIBUTORS BE
   LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   POSSIBILITY OF SUCH DAMAGE.
*/

/* This implementation is optimized for performance.  For code size a generic
   implementation of this function from newlib/libc/string/strcmp.c will be
   used.  */
#if !defined (__OPTIMIZE_SIZE__) && !defined (PREFER_SIZE_OVER_SPEED)

#include "asm.h"

/* This is optimized primarily for the ARC700.
   It would be possible to speed up the loops by one cycle / word
   respective one cycle / byte by forcing double source 1 alignment, unrolling
   by a factor of two, and speculatively loading the second word / byte of
   source 1; however, that would increase the overhead for loop setup / finish,
   and strcmp might often terminate early.  */
#ifndef __ARCHS__

ENTRY (strcmp)
        or      r2,r0,r1
        bmsk_s  r2,r2,1
        brne_l  r2,0,.Lcharloop
        mov_s   r12,0x01010101
        ror     r5,r12
.Lwordloop:
        ld.ab   r2,[r0,4]
        ld.ab   r3,[r1,4]
        nop_s
        sub     r4,r2,r12
        bic     r4,r4,r2
        and     r4,r4,r5
        brne_l  r4,0,.Lfound0
        breq    r2,r3,.Lwordloop
#ifdef  __LITTLE_ENDIAN__
        xor     r0,r2,r3        ; mask for difference
        sub_s   r1,r0,1
        bic_s   r0,r0,r1        ; mask for least significant difference bit
        sub     r1,r5,r0
        xor     r0,r5,r1        ; mask for least significant difference byte
        and_s   r2,r2,r0
        and_s   r3,r3,r0
#endif /* LITTLE ENDIAN */
        cmp_s   r2,r3
        mov_s   r0,1
        j_s.d   [blink]
        bset.lo r0,r0,31

        .balign 4
#ifdef __LITTLE_ENDIAN__
.Lfound0:
        xor     r0,r2,r3        ; mask for difference
        or      r0,r0,r4        ; or in zero indicator
        sub_s   r1,r0,1
        bic_s   r0,r0,r1        ; mask for least significant difference bit
        sub     r1,r5,r0
        xor     r0,r5,r1        ; mask for least significant difference byte
        and_s   r2,r2,r0
        and_s   r3,r3,r0
        sub.f   r0,r2,r3
        mov.hi  r0,1
        j_s.d   [blink]
        bset.lo r0,r0,31
#else /* BIG ENDIAN */
        /* The zero-detection above can mis-detect 0x01 bytes as zeroes
           because of carry-propagateion from a lower significant zero byte.
           We can compensate for this by checking that bit0 is zero.
           This compensation is not necessary in the step where we
           get a low estimate for r2, because in any affected bytes
           we already have 0x00 or 0x01, which will remain unchanged
           when bit 7 is cleared.  */
        .balign 4
.Lfound0:
#ifdef __ARC_BARREL_SHIFTER__
        lsr     r0,r4,8
        lsr_s   r1,r2
        bic_s   r2,r2,r0        ; get low estimate for r2 and get ...
        bic_s   r0,r0,r1        ; <this is the adjusted mask for zeros>
        or_s    r3,r3,r0        ; ... high estimate r3 so that r2 > r3 will ...
        cmp_s   r3,r2           ; ... be independent of trailing garbage
        or_s    r2,r2,r0        ; likewise for r3 > r2
        bic_s   r3,r3,r0
        rlc     r0,0            ; r0 := r2 > r3 ? 1 : 0
        cmp_s   r2,r3
        j_s.d   [blink]
        bset.lo r0,r0,31
#else /* __ARC_BARREL_SHIFTER__ */
        /* Fall through to .Lcharloop.  */
        sub_s   r0,r0,4
        sub_s   r1,r1,4
#endif /* __ARC_BARREL_SHIFTER__ */
#endif /* ENDIAN */

        .balign 4
.Lcharloop:
        ldb.ab  r2,[r0,1]
        ldb.ab  r3,[r1,1]
        nop_s
        breq_l  r2,0,.Lcmpend
        breq    r2,r3,.Lcharloop
.Lcmpend:
        j_s.d   [blink]
        sub     r0,r2,r3
ENDFUNC (strcmp)
#endif /* !__ARCHS__ */

#endif /* !__OPTIMIZE_SIZE__ && !PREFER_SIZE_OVER_SPEED */