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/*
* BIRD Library -- IP One-Complement Checksum
*
* (c) 1999--2000 Martin Mares <mj@ucw.cz>
*
* Can be freely distributed and used under the terms of the GNU GPL.
*/
/**
* DOC: Miscellaneous functions.
*/
#include <stdarg.h>
#include "nest/bird.h"
#include "checksum.h"
static u16 /* One-complement addition */
add16(u16 sum, u16 x)
{
u16 z = sum + x;
return z + (z < sum);
}
static u32
add32(u32 sum, u32 x)
{
u32 z = sum + x;
return z + (z < sum);
}
static u16
ipsum_calc_block(u16 *x, unsigned len, u16 sum)
{
int rest;
u32 tmp, *xx;
/*
* A few simple facts about the IP checksum (see RFC 1071 for detailed
* discussion):
*
* o It's associative and commutative.
* o It's byte order independent.
* o It's word size independent.
*
* This gives us a neat 32-bits-at-a-time algorithm which respects
* usual alignment requirements and is reasonably fast.
*/
ASSERT(!(len % 2));
if (!len)
return sum;
len >>= 1;
if ((unsigned long) x & 2) /* Align to 32-bit boundary */
{
sum = add16(sum, *x++);
len--;
}
rest = len & 1;
len >>= 1;
tmp = 0;
xx = (u32 *) x;
while (len)
{
tmp = add32(tmp, *xx++);
len--;
}
sum = add16(sum, add16(tmp & 0xffff, tmp >> 16U));
if (rest)
sum = add16(sum, *(u16 *) xx);
return sum;
}
static u16
ipsum_calc(void *frag, unsigned len, va_list args)
{
u16 sum = 0;
for(;;)
{
sum = ipsum_calc_block(frag, len, sum);
frag = va_arg(args, void *);
if (!frag)
break;
len = va_arg(args, unsigned);
}
return sum;
}
/**
* ipsum_verify - verify an IP checksum
* @frag: first packet fragment
* @len: length in bytes
*
* This function verifies whether a given fragmented packet
* has correct one's complement checksum as used by the IP
* protocol.
*
* It uses all the clever tricks described in RFC 1071 to speed
* up checksum calculation as much as possible.
*
* Result: 1 if the checksum is correct, 0 else.
*/
int
ipsum_verify(void *frag, unsigned len, ...)
{
va_list args;
u16 sum;
va_start(args, len);
sum = ipsum_calc(frag, len, args);
va_end(args);
return sum == 0xffff;
}
/**
* ipsum_calculate - compute an IP checksum
* @frag: first packet fragment
* @len: length in bytes
*
* This function caculates a one's complement checksum of a given fragmented
* packet.
*
* It uses all the clever tricks described in RFC 1071 to speed
* up checksum calculation as much as possible.
*/
u16
ipsum_calculate(void *frag, unsigned len, ...)
{
va_list args;
u16 sum;
va_start(args, len);
sum = ipsum_calc(frag, len, args);
va_end(args);
return 0xffff - sum;
}
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