109 lines
1.9 KiB
C
109 lines
1.9 KiB
C
/*
|
|
* BIRD Library -- IP One-Complement Checksum
|
|
*
|
|
* (c) 1999 Martin Mares <mj@ucw.cz>
|
|
*
|
|
* Can be freely distributed and used under the terms of the GNU GPL.
|
|
*/
|
|
|
|
#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;
|
|
}
|
|
|
|
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;
|
|
}
|
|
|
|
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;
|
|
}
|