2 * Copyright (c) 2003 Matthew Dillon <dillon@backplane.com>
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * $DragonFly: src/sys/cpu/i386/misc/in_cksum2.s,v 1.1 2004/02/14 02:09:26 dillon Exp $
29 #include <machine/asmacros.h> /* miscellaneous asm macros */
30 #include <machine/apic.h>
31 #include <machine/specialreg.h>
38 * asm_ones32(32bitalignedbuffer, numberof32bitwords)
40 * Returns the 32 bit one complement partial checksum. This is
41 * basically a 1's complement checksum without the inversion (~)
42 * at the end. A 32 bit value is returned. If the caller is
43 * calculating a 16 bit 1's complement checksum the caller must
44 * collapse the 32 bit return value via:
46 * result = (result >> 16) + (result & 0xFFFF)
47 * if (result > 0xFFFF)
48 * result -= 0xFFFF; <<< same as (result + 1) & 0xFFFF
49 * within the range of result.
50 * Note that worst case 0xFFFFFFFF + 0xFFFFFFFF = 0xFFFFFFFE + CARRY,
51 * so no double-carry ever occurs.
55 movl 4(%esp),%edx /* %edx = buffer pointer */
56 movl 8(%esp),%ecx /* %ecx = counter */
57 subl %eax,%eax /* %eax = checksum */