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[tcpip] Add faster algorithm for calculating the TCP/IP checksum
The generic TCP/IP checksum implementation requires approximately 10 CPU clocks per byte (as measured using the TSC). Improve this to approximately 0.5 CPU clocks per byte by using "lodsl ; adcl" in an unrolled loop. Signed-off-by: Michael Brown <mcb30@ipxe.org>
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Michael Brown
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169
src/arch/x86/core/x86_tcpip.c
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169
src/arch/x86/core/x86_tcpip.c
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/*
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* Copyright (C) 2012 Michael Brown <mbrown@fensystems.co.uk>.
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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 License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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* 02110-1301, USA.
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*/
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FILE_LICENCE ( GPL2_OR_LATER );
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/** @file
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*
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* TCP/IP checksum
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*
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*/
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#include <limits.h>
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#include <ipxe/tcpip.h>
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extern char x86_tcpip_loop_end[];
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/**
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* Calculate continued TCP/IP checkum
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*
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* @v partial Checksum of already-summed data, in network byte order
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* @v data Data buffer
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* @v len Length of data buffer
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* @ret cksum Updated checksum, in network byte order
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*/
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uint16_t x86_tcpip_continue_chksum ( uint16_t partial,
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const void *data, size_t len ) {
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unsigned long sum = ( ( ~partial ) & 0xffff );
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unsigned long initial_word_count;
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unsigned long loop_count;
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unsigned long loop_partial_count;
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unsigned long final_word_count;
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unsigned long final_byte;
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unsigned long discard_S;
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unsigned long discard_c;
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unsigned long discard_a;
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unsigned long discard_r1;
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unsigned long discard_r2;
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/* Calculate number of initial 16-bit words required to bring
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* the main loop into alignment. (We don't care about the
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* speed for data aligned to less than 16 bits, since this
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* situation won't occur in practice.)
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*/
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if ( len >= sizeof ( sum ) ) {
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initial_word_count = ( ( -( ( intptr_t ) data ) &
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( sizeof ( sum ) - 1 ) ) >> 1 );
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} else {
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initial_word_count = 0;
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}
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len -= ( initial_word_count * 2 );
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/* Calculate number of iterations of the main loop. This loop
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* processes native machine words (32-bit or 64-bit), and is
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* unrolled 16 times. We calculate an overall iteration
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* count, and a starting point for the first iteration.
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*/
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loop_count = ( len / ( sizeof ( sum ) * 16 ) );
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loop_partial_count =
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( ( len % ( sizeof ( sum ) * 16 ) ) / sizeof ( sum ) );
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/* Calculate number of 16-bit words remaining after the main
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* loop completes.
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*/
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final_word_count = ( ( len % sizeof ( sum ) ) / 2 );
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/* Calculate whether or not a final byte remains at the end */
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final_byte = ( len & 1 );
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/* Calculate the checksum */
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__asm__ ( /* Calculate position at which to jump into the
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* unrolled loop.
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*/
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"imul $( -x86_tcpip_loop_step_size ), %4\n\t"
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"add %5, %4\n\t"
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/* Clear carry flag before starting checksumming */
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"clc\n\t"
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/* Checksum initial words */
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"jmp 2f\n\t"
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"\n1:\n\t"
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"lodsw\n\t"
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"adcw %w2, %w0\n\t"
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"\n2:\n\t"
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"loop 1b\n\t"
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/* Main "lods;adc" loop, unrolled x16 */
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"mov %12, %3\n\t"
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"jmp *%4\n\t"
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"\nx86_tcpip_loop_start:\n\t"
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"lods%z2\n\tadc %2, %0\n\t"
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"lods%z2\n\tadc %2, %0\n\t"
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"lods%z2\n\tadc %2, %0\n\t"
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"lods%z2\n\tadc %2, %0\n\t"
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"lods%z2\n\tadc %2, %0\n\t"
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"lods%z2\n\tadc %2, %0\n\t"
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"lods%z2\n\tadc %2, %0\n\t"
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"lods%z2\n\tadc %2, %0\n\t"
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"lods%z2\n\tadc %2, %0\n\t"
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"lods%z2\n\tadc %2, %0\n\t"
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"lods%z2\n\tadc %2, %0\n\t"
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"lods%z2\n\tadc %2, %0\n\t"
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"lods%z2\n\tadc %2, %0\n\t"
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"lods%z2\n\tadc %2, %0\n\t"
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"lods%z2\n\tadc %2, %0\n\t"
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"lods%z2\n\tadc %2, %0\n\t"
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"\nx86_tcpip_loop_end:\n\t"
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"loop x86_tcpip_loop_start\n\t"
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".equ x86_tcpip_loop_step_size, "
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" ( ( x86_tcpip_loop_end - x86_tcpip_loop_start ) / 16 )\n\t"
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/* Checksum remaining whole words */
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"mov %13, %3\n\t"
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"jmp 2f\n\t"
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"\n1:\n\t"
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"lodsw\n\t"
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"adcw %w2, %w0\n\t"
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"\n2:\n\t"
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"loop 1b\n\t"
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/* Checksum final byte if applicable */
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"mov %14, %3\n\t"
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"loop 1f\n\t"
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"adcb (%1), %b0\n\t"
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"adcb $0, %h0\n\t"
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"\n1:\n\t"
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/* Fold down to a uint16_t */
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"push %0\n\t"
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"popw %w0\n\t"
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"popw %w2\n\t"
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"adcw %w2, %w0\n\t"
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#if ULONG_MAX > 0xffffffffUL /* 64-bit only */
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"popw %w2\n\t"
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"adcw %w2, %w0\n\t"
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"popw %w2\n\t"
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"adcw %w2, %w0\n\t"
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#endif /* 64-bit only */
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/* Consume CF */
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"adcw $0, %w0\n\t"
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"adcw $0, %w0\n\t"
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: "=&Q" ( sum ), "=&S" ( discard_S ), "=&a" ( discard_a ),
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"=&c" ( discard_c ), "=&r" ( discard_r1 ),
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"=&r" ( discard_r2 )
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: "0" ( sum ), "1" ( data ), "2" ( 0 ),
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"3" ( initial_word_count + 1 ), "4" ( loop_partial_count ),
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"5" ( x86_tcpip_loop_end ), "g" ( loop_count + 1 ),
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"g" ( final_word_count + 1 ), "g" ( final_byte ) );
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return ( ~sum & 0xffff );
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}
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@ -9,4 +9,9 @@
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FILE_LICENCE ( GPL2_OR_LATER );
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extern uint16_t x86_tcpip_continue_chksum ( uint16_t partial,
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const void *data, size_t len );
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#define tcpip_continue_chksum x86_tcpip_continue_chksum
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#endif /* _BITS_TCPIP_H */
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