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/*
*
* INET An implementation of the TCP/IP protocol suite for the LINUX
* operating system. INET is implemented using the BSD Socket
* interface as the means of communication with the user level.
*
* IP/TCP/UDP checksumming routines
*
* Authors: Jorge Cwik, <jorge@laser.satlink.net>
* Arnt Gulbrandsen, <agulbra@nvg.unit.no>
* Tom May, <ftom@netcom.com>
* Andreas Schwab, <schwab@issan.informatik.uni-dortmund.de>
* Lots of code moved from tcp.c and ip.c; see those files
* for more names.
*
* 03/02/96 Jes Sorensen, Andreas Schwab, Roman Hodek:
* Fixed some nasty bugs, causing some horrible crashes.
* A: At some points, the sum (%0) was used as
* length-counter instead of the length counter
* (%1). Thanks to Roman Hodek for pointing this out.
* B: GCC seems to mess up if one uses too many
* data-registers to hold input values and one tries to
* specify d0 and d1 as scratch registers. Letting gcc
* choose these registers itself solves the problem.
*
* 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.
*/
/* Based on code from the Linux kernel. */
#include <assert.h>
#include <endian.h>
#include <stdint.h>
#include "checksum.h"
/* Revised by Kenneth Albanowski for m68knommu. Basic problem: unaligned access
kills, so most of the assembly has to go. */
static inline uint16_t from32to16(uint32_t x)
{
/* add up 16-bit and 16-bit for 16+c bit */
x = (x & 0xffff) + (x >> 16);
/* add up carry.. */
x = (x & 0xffff) + (x >> 16);
return (uint16_t)x;
}
static uint16_t do_csum(const unsigned char *buff, int len)
{
int odd;
unsigned int result = 0;
if (len <= 0)
goto out;
odd = 1 & (unsigned long) buff;
if (odd) {
#if __BYTE_ORDER == __LITTLE_ENDIAN
result += ((unsigned int)(*buff) << 8);
#else
result = *buff;
#endif
len--;
buff++;
}
assert(!((unsigned long)buff & 1));
if (len >= 2) {
if (2 & (const unsigned long) buff) {
result += *(const unsigned short *) buff;
len -= 2;
buff += 2;
}
assert(!((unsigned long)buff & 2));
if (len >= 4) {
const unsigned char *end = buff + ((unsigned)len & ~3u);
unsigned int carry = 0;
do {
unsigned int w = *(const unsigned int *) buff;
buff += 4;
result += carry;
result += w;
carry = (w > result);
} while (buff < end);
result += carry;
result = (result & 0xffff) + (result >> 16);
}
if (len & 2) {
result += *(const unsigned short *) buff;
buff += 2;
}
}
if (len & 1)
#if __BYTE_ORDER == __LITTLE_ENDIAN
result += *buff;
#else
result += (*buff << 8);
#endif
result = from32to16(result);
if (odd)
result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
out:
return (uint16_t)result;
}
/*
* computes the checksum of a memory block at buff, length len,
* and adds in "sum" (32-bit)
*
* returns a 32-bit number suitable for feeding into itself
* or csum_tcpudp_magic
*
* this function must be called with even lengths, except
* for the last fragment, which may be odd
*
* it's best to have buff aligned on a 32-bit boundary
*/
uint16_t csum_partial(const void *buff, int len, uint16_t wsum)
{
uint16_t sum = wsum;
uint16_t result = do_csum(buff, len);
/* add in old sum, and carry.. */
result += sum;
if (sum > result)
result += 1;
return result;
}
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