usr/src/lib/libc/mips/string/bcmp.s

/*-
 * Copyright (c) 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Ralph Campbell.
 *
 * %sccs.include.redist.c%
 */

#include <machine/machAsmDefs.h>

#if defined(LIBC_SCCS) && !defined(lint)
        ASMSTR("@(#)bcmp.s      8.1 (Berkeley) %G%")
#endif /* LIBC_SCCS and not lint */

/* bcmp(s1, s2, n) */

#ifdef MIPSEL
#       define  LWHI    lwr
#       define  LWLO    lwl
#       define  SWHI    swr
#       define  SWLO    swl
#endif
#ifdef MIPSEB
#       define  LWHI    lwl
#       define  LWLO    lwr
#       define  SWHI    swl
#       define  SWLO    swr
#endif

LEAF(bcmp)
        .set    noreorder
        blt     a2, 16, small           # is it worth any trouble?
        xor     v0, a0, a1              # compare low two bits of addresses
        and     v0, v0, 3
        subu    a3, zero, a1            # compute # bytes to word align address
        bne     v0, zero, unaligned     # not possible to align addresses
        and     a3, a3, 3

        beq     a3, zero, 1f
        subu    a2, a2, a3              # subtract from remaining count
        move    v0, v1                  # init v0,v1 so unmodified bytes match
        LWHI    v0, 0(a0)               # read 1, 2, or 3 bytes
        LWHI    v1, 0(a1)
        addu    a1, a1, a3
        bne     v0, v1, nomatch
        addu    a0, a0, a3
1:
        and     a3, a2, ~3              # compute number of whole words left
        subu    a2, a2, a3              #   which has to be >= (16-3) & ~3
        addu    a3, a3, a0              # compute ending address
2:
        lw      v0, 0(a0)               # compare words
        lw      v1, 0(a1)
        addu    a0, a0, 4
        bne     v0, v1, nomatch
        addu    a1, a1, 4
        bne     a0, a3, 2b
        nop
        b       small                   # finish remainder
        nop
unaligned:
        beq     a3, zero, 2f
        subu    a2, a2, a3              # subtract from remaining count
        addu    a3, a3, a0              # compute ending address
1:
        lbu     v0, 0(a0)               # compare bytes until a1 word aligned
        lbu     v1, 0(a1)
        addu    a0, a0, 1
        bne     v0, v1, nomatch
        addu    a1, a1, 1
        bne     a0, a3, 1b
        nop
2:
        and     a3, a2, ~3              # compute number of whole words left
        subu    a2, a2, a3              #   which has to be >= (16-3) & ~3
        addu    a3, a3, a0              # compute ending address
3:
        LWHI    v0, 0(a0)               # compare words a0 unaligned, a1 aligned
        LWLO    v0, 3(a0)
        lw      v1, 0(a1)
        addu    a0, a0, 4
        bne     v0, v1, nomatch
        addu    a1, a1, 4
        bne     a0, a3, 3b
        nop
small:
        ble     a2, zero, match
        addu    a3, a2, a0              # compute ending address
1:
        lbu     v0, 0(a0)
        lbu     v1, 0(a1)
        addu    a0, a0, 1
        bne     v0, v1, nomatch
        addu    a1, a1, 1
        bne     a0, a3, 1b
        nop
match:
        j       ra
        move    v0, zero
nomatch:
        j       ra
        li      v0, 1
        .set    reorder
END(bcmp)