Hi, this regards the function 'csum_partial' that is in the file
linux/arch/mips/lib-64/csum_partial.S.
Towards the end, we label
maybe_end_cruft:
andi ta2, a1, 0x3
and then
small_memcpy:
...
The comments for small_csumcpy says: 'unknown src alignment and < 8 bytes
to go'.
But as I see the checksum computation for buffers containing fewer than 8
bytes is taken care at the beginning of the 'csum_partial' function. So,
what purpose is it serving at the end of 'csum_partial' ? Can someone
please clarify ?
thank you,
Prasad
-----------------------------------------------------------------------------
/*
* a0: source address
* a1: length of the area to checksum
* a2: partial checksum
*/
#define src a0
#define sum v0
.text
.set noreorder
/* unknown src alignment and < 8 bytes to go */
small_csumcpy:
move a1, ta2
andi ta0, a1, 4
beqz ta0, 1f
andi ta0, a1, 2
/* Still a full word to go */
ulw ta1, (src)
daddiu src, 4
ADDC(sum, ta1)
1: move ta1, zero
beqz ta0, 1f
andi ta0, a1, 1
/* Still a halfword to go */
ulhu ta1, (src)
daddiu src, 2
1: beqz ta0, 1f
sll ta1, ta1, 16
lbu ta2, (src)
nop
#ifdef __MIPSEB__
sll ta2, ta2, 8
#endif
or ta1, ta2
1: ADDC(sum, ta1)
/* fold checksum */
sll v1, sum, 16
addu sum, v1
sltu v1, sum, v1
srl sum, sum, 16
addu sum, v1
/* odd buffer alignment? */
beqz t3, 1f
nop
sll v1, sum, 8
srl sum, sum, 8
or sum, v1
andi sum, 0xffff
1:
.set reorder
/* Add the passed partial csum. */
ADDC(sum, a2)
jr ra
.set noreorder
/* ------------------------------------------------------------------------- */
.align 5
LEAF(csum_partial)
move sum, zero
move t3, zero
sltiu t8, a1, 0x8
bnez t8, small_csumcpy /* < 8 bytes to copy */
move ta2, a1
beqz a1, out
andi t3, src, 0x1 /* odd buffer? */
hword_align:
beqz t3, word_align
andi t8, src, 0x2
lbu ta0, (src)
dsubu a1, a1, 0x1
#ifdef __MIPSEL__
sll ta0, ta0, 8
#endif
ADDC(sum, ta0)
daddu src, src, 0x1
andi t8, src, 0x2
word_align:
beqz t8, dword_align
sltiu t8, a1, 56
lhu ta0, (src)
dsubu a1, a1, 0x2
ADDC(sum, ta0)
sltiu t8, a1, 56
daddu src, src, 0x2
dword_align:
bnez t8, do_end_words
move t8, a1
andi t8, src, 0x4
beqz t8, qword_align
andi t8, src, 0x8
lw ta0, 0x00(src)
dsubu a1, a1, 0x4
ADDC(sum, ta0)
daddu src, src, 0x4
andi t8, src, 0x8
qword_align:
beqz t8, oword_align
andi t8, src, 0x10
lw ta0, 0x00(src)
lw ta1, 0x04(src)
dsubu a1, a1, 0x8
ADDC(sum, ta0)
ADDC(sum, ta1)
daddu src, src, 0x8
andi t8, src, 0x10
oword_align:
beqz t8, begin_movement
dsrl t8, a1, 0x7
lw ta3, 0x08(src)
lw t0, 0x0c(src)
lw ta0, 0x00(src)
lw ta1, 0x04(src)
ADDC(sum, ta3)
ADDC(sum, t0)
ADDC(sum, ta0)
ADDC(sum, ta1)
dsubu a1, a1, 0x10
daddu src, src, 0x10
dsrl t8, a1, 0x7
begin_movement:
beqz t8, 1f
andi ta2, a1, 0x40
move_128bytes:
CSUM_BIGCHUNK(src, 0x00, sum, ta0, ta1, ta3, t0)
CSUM_BIGCHUNK(src, 0x20, sum, ta0, ta1, ta3, t0)
CSUM_BIGCHUNK(src, 0x40, sum, ta0, ta1, ta3, t0)
CSUM_BIGCHUNK(src, 0x60, sum, ta0, ta1, ta3, t0)
dsubu t8, t8, 0x01
bnez t8, move_128bytes
daddu src, src, 0x80
1:
beqz ta2, 1f
andi ta2, a1, 0x20
move_64bytes:
CSUM_BIGCHUNK(src, 0x00, sum, ta0, ta1, ta3, t0)
CSUM_BIGCHUNK(src, 0x20, sum, ta0, ta1, ta3, t0)
daddu src, src, 0x40
1:
beqz ta2, do_end_words
andi t8, a1, 0x1c
move_32bytes:
CSUM_BIGCHUNK(src, 0x00, sum, ta0, ta1, ta3, t0)
andi t8, a1, 0x1c
daddu src, src, 0x20
do_end_words:
beqz t8, maybe_end_cruft
dsrl t8, t8, 0x2
end_words:
lw ta0, (src)
dsubu t8, t8, 0x1
ADDC(sum, ta0)
bnez t8, end_words
daddu src, src, 0x4
maybe_end_cruft:
andi ta2, a1, 0x3
small_memcpy:
j small_csumcpy; move a1, ta2 /* XXX ??? */
beqz t2, out
move a1, ta2
end_bytes:
lb ta0, (src)
dsubu a1, a1, 0x1
bnez a2, end_bytes
daddu src, src, 0x1
out:
jr ra
move v0, sum
END(csum_partial)
