123 lines
2.4 KiB
C
123 lines
2.4 KiB
C
/*
|
|
* 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 inline u32
|
|
add32(u32 sum, u32 x)
|
|
{
|
|
u32 z = sum + x;
|
|
// return z + (z < sum);
|
|
|
|
/* add carry */
|
|
if (z < x)
|
|
z++;
|
|
return z;
|
|
}
|
|
|
|
static u16
|
|
ipsum_calc_block(u32 *buf, uint len, u16 isum)
|
|
{
|
|
/*
|
|
* 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 % 4));
|
|
if (!len)
|
|
return isum;
|
|
|
|
u32 *end = buf + (len >> 2);
|
|
u32 sum = isum;
|
|
while (buf < end)
|
|
sum = add32(sum, *buf++);
|
|
|
|
sum = (sum >> 16) + (sum & 0xffff); /* add high-16 to low-16 */
|
|
sum += (sum >> 16); /* add carry */
|
|
return sum;
|
|
}
|
|
|
|
static u16
|
|
ipsum_calc(void *frag, uint 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, uint);
|
|
}
|
|
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, uint 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 calculates 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, uint len, ...)
|
|
{
|
|
va_list args;
|
|
u16 sum;
|
|
|
|
va_start(args, len);
|
|
sum = ipsum_calc(frag, len, args);
|
|
va_end(args);
|
|
return 0xffff - sum;
|
|
}
|