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#include "DEFS.h"
/*
* bcmp(s1, s2, n)
*/
LEAF(bcmp)
.set noreorder
blt a2, 16, smallcmp # 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, unalignedcmp # 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 smallcmp # finish remainder
nop
unalignedcmp:
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
smallcmp:
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
END(bcmp)
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