2 * Copyright (c) 2003,2004,2008 The DragonFly Project. All rights reserved.
4 * This code is derived from software contributed to The DragonFly Project
5 * by Matthew Dillon <dillon@backplane.com>
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in
15 * the documentation and/or other materials provided with the
17 * 3. Neither the name of The DragonFly Project nor the names of its
18 * contributors may be used to endorse or promote products derived
19 * from this software without specific, prior written permission.
21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
22 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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24 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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31 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35 #include <machine/asmacros.h> /* miscellaneous asm macros */
42 * asm_ones32(32bitalignedbuffer, numberof32bitwords)
44 * Returns the 32 bit one complement partial checksum. This is
45 * basically a 1's complement checksum without the inversion (~)
46 * at the end. A 32 bit value is returned. If the caller is
47 * calculating a 16 bit 1's complement checksum the caller must
48 * collapse the 32 bit return value via:
50 * result = (result >> 16) + (result & 0xFFFF)
51 * if (result > 0xFFFF)
52 * result -= 0xFFFF; <<< same as (result + 1) & 0xFFFF
53 * within the range of result.
54 * Note that worst case 0xFFFFFFFF + 0xFFFFFFFF = 0xFFFFFFFE + CARRY,
55 * so no double-carry ever occurs.
59 movq
%rdi
,%rdx
/* %rdx = buffer pointer */
60 movl
%esi
,%ecx
/* %ecx = counter */
61 xorl
%eax
,%eax
/* %eax = checksum */