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    Subject[PATCH 32/43] MN10300: Optimise do_csum()
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    Date
    From: Akira Takeuchi <takeuchi.akr@jp.panasonic.com>

    Optimise do_csum() to gang up the loads so they're less likely to get
    interruptions between.

    Signed-off-by: Akira Takeuchi <takeuchi.akr@jp.panasonic.com>
    Signed-off-by: Kiyoshi Owada <owada.kiyoshi@jp.panasonic.com>
    Signed-off-by: David Howells <dhowells@redhat.com>
    ---

    arch/mn10300/lib/do_csum.S | 49 ++++++++++++++++++++------------------------
    1 files changed, 22 insertions(+), 27 deletions(-)


    diff --git a/arch/mn10300/lib/do_csum.S b/arch/mn10300/lib/do_csum.S
    index e138994..1d27bba 100644
    --- a/arch/mn10300/lib/do_csum.S
    +++ b/arch/mn10300/lib/do_csum.S
    @@ -10,26 +10,25 @@
    */
    #include <asm/cache.h>

    - .section .text
    - .balign L1_CACHE_BYTES
    + .section .text
    + .balign L1_CACHE_BYTES

    ###############################################################################
    #
    -# unsigned int do_csum(const unsigned char *buff, size_t len)
    +# unsigned int do_csum(const unsigned char *buff, int len)
    #
    ###############################################################################
    .globl do_csum
    - .type do_csum,@function
    + .type do_csum,@function
    do_csum:
    movm [d2,d3],(sp)
    - mov d0,(12,sp)
    - mov d1,(16,sp)
    mov d1,d2 # count
    mov d0,a0 # buff
    + mov a0,a1
    clr d1 # accumulator

    cmp +0,d2
    - beq do_csum_done # return if zero-length buffer
    + ble do_csum_done # check for zero length or negative

    # 4-byte align the buffer pointer
    btst +3,a0
    @@ -41,17 +40,15 @@ do_csum:
    inc a0
    asl +8,d0
    add d0,d1
    - addc +0,d1
    add -1,d2
    -do_csum_addr_not_odd:

    +do_csum_addr_not_odd:
    cmp +2,d2
    bcs do_csum_fewer_than_4
    btst +2,a0
    beq do_csum_now_4b_aligned
    movhu (a0+),d0
    add d0,d1
    - addc +0,d1
    add -2,d2
    cmp +4,d2
    bcs do_csum_fewer_than_4
    @@ -66,20 +63,20 @@ do_csum_now_4b_aligned:

    do_csum_loop:
    mov (a0+),d0
    - add d0,d1
    mov (a0+),e0
    - addc e0,d1
    mov (a0+),e1
    - addc e1,d1
    mov (a0+),e3
    + add d0,d1
    + addc e0,d1
    + addc e1,d1
    addc e3,d1
    mov (a0+),d0
    - addc d0,d1
    mov (a0+),e0
    - addc e0,d1
    mov (a0+),e1
    - addc e1,d1
    mov (a0+),e3
    + addc d0,d1
    + addc e0,d1
    + addc e1,d1
    addc e3,d1
    addc +0,d1

    @@ -94,12 +91,12 @@ do_csum_remainder:
    cmp +16,d2
    bcs do_csum_fewer_than_16
    mov (a0+),d0
    - add d0,d1
    mov (a0+),e0
    - addc e0,d1
    mov (a0+),e1
    - addc e1,d1
    mov (a0+),e3
    + add d0,d1
    + addc e0,d1
    + addc e1,d1
    addc e3,d1
    addc +0,d1
    add -16,d2
    @@ -131,9 +128,9 @@ do_csum_fewer_than_4:
    xor_cmp d0,d0,+2,d2
    bcs do_csum_fewer_than_2
    movhu (a0+),d0
    -do_csum_fewer_than_2:
    and +1,d2
    beq do_csum_add_last_bit
    +do_csum_fewer_than_2:
    movbu (a0),d3
    add d3,d0
    do_csum_add_last_bit:
    @@ -142,21 +139,19 @@ do_csum_add_last_bit:

    do_csum_done:
    # compress the checksum down to 16 bits
    - mov +0xffff0000,d2
    - and d1,d2
    + mov +0xffff0000,d0
    + and d1,d0
    asl +16,d1
    - add d2,d1,d0
    + add d1,d0
    addc +0xffff,d0
    lsr +16,d0

    # flip the halves of the word result if the buffer was oddly aligned
    - mov (12,sp),d1
    - and +1,d1
    + and +1,a1
    beq do_csum_not_oddly_aligned
    swaph d0,d0 # exchange bits 15:8 with 7:0

    do_csum_not_oddly_aligned:
    ret [d2,d3],8

    -do_csum_end:
    - .size do_csum, do_csum_end-do_csum
    + .size do_csum, .-do_csum


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