158 строки
2.8 KiB
ArmAsm
158 строки
2.8 KiB
ArmAsm
/* Optimised simple memory checksum
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*
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* Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public Licence
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* as published by the Free Software Foundation; either version
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* 2 of the Licence, or (at your option) any later version.
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*/
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#include <asm/cache.h>
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.section .text
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.balign L1_CACHE_BYTES
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###############################################################################
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#
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# unsigned int do_csum(const unsigned char *buff, int len)
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#
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###############################################################################
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.globl do_csum
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.type do_csum,@function
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do_csum:
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movm [d2,d3],(sp)
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mov d1,d2 # count
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mov d0,a0 # buff
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mov a0,a1
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clr d1 # accumulator
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cmp +0,d2
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ble do_csum_done # check for zero length or negative
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# 4-byte align the buffer pointer
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btst +3,a0
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beq do_csum_now_4b_aligned
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btst +1,a0
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beq do_csum_addr_not_odd
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movbu (a0),d0
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inc a0
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asl +8,d0
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add d0,d1
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add -1,d2
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do_csum_addr_not_odd:
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cmp +2,d2
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bcs do_csum_fewer_than_4
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btst +2,a0
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beq do_csum_now_4b_aligned
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movhu (a0+),d0
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add d0,d1
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add -2,d2
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cmp +4,d2
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bcs do_csum_fewer_than_4
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do_csum_now_4b_aligned:
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# we want to checksum as much as we can in chunks of 32 bytes
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cmp +31,d2
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bls do_csum_remainder # 4-byte aligned remainder
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add -32,d2
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mov +32,d3
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do_csum_loop:
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mov (a0+),d0
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mov (a0+),e0
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mov (a0+),e1
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mov (a0+),e3
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add d0,d1
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addc e0,d1
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addc e1,d1
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addc e3,d1
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mov (a0+),d0
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mov (a0+),e0
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mov (a0+),e1
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mov (a0+),e3
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addc d0,d1
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addc e0,d1
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addc e1,d1
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addc e3,d1
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addc +0,d1
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sub d3,d2
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bcc do_csum_loop
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add d3,d2
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beq do_csum_done
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do_csum_remainder:
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# cut 16-31 bytes down to 0-15
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cmp +16,d2
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bcs do_csum_fewer_than_16
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mov (a0+),d0
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mov (a0+),e0
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mov (a0+),e1
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mov (a0+),e3
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add d0,d1
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addc e0,d1
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addc e1,d1
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addc e3,d1
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addc +0,d1
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add -16,d2
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beq do_csum_done
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do_csum_fewer_than_16:
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# copy the remaining whole words
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cmp +4,d2
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bcs do_csum_fewer_than_4
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cmp +8,d2
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bcs do_csum_one_word
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cmp +12,d2
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bcs do_csum_two_words
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mov (a0+),d0
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add d0,d1
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addc +0,d1
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do_csum_two_words:
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mov (a0+),d0
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add d0,d1
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addc +0,d1
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do_csum_one_word:
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mov (a0+),d0
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add d0,d1
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addc +0,d1
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do_csum_fewer_than_4:
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and +3,d2
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beq do_csum_done
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xor_cmp d0,d0,+2,d2
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bcs do_csum_fewer_than_2
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movhu (a0+),d0
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and +1,d2
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beq do_csum_add_last_bit
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do_csum_fewer_than_2:
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movbu (a0),d3
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add d3,d0
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do_csum_add_last_bit:
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add d0,d1
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addc +0,d1
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do_csum_done:
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# compress the checksum down to 16 bits
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mov +0xffff0000,d0
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and d1,d0
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asl +16,d1
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add d1,d0
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addc +0xffff,d0
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lsr +16,d0
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# flip the halves of the word result if the buffer was oddly aligned
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and +1,a1
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beq do_csum_not_oddly_aligned
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swaph d0,d0 # exchange bits 15:8 with 7:0
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do_csum_not_oddly_aligned:
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ret [d2,d3],8
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.size do_csum, .-do_csum
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