[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>

src/arch/x86/core/x86_tcpip.c

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

src/arch/x86/include/bits/tcpip.h

@@ -9,4 +9,9 @@
 
 FILE_LICENCE ( GPL2_OR_LATER );
 
+extern uint16_t x86_tcpip_continue_chksum ( uint16_t partial,
+					    const void *data, size_t len );
+
+#define tcpip_continue_chksum x86_tcpip_continue_chksum
+
 #endif /* _BITS_TCPIP_H */