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Implements changes in checksum alg suggested by Joakim Tjernlund.

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This commit is contained in:
Ondrej Zajicek 2010-04-25 19:13:49 +02:00
parent 0ea8fb4abe
commit c1b51598d4
1 changed files with 18 additions and 33 deletions
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51
lib/checksum.c
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@ -15,26 +15,21 @@
#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
static inline u32
add32(u32 sum, u32 x)
{
u32 z = sum + x;
return z + (z < sum);
// return z + (z < sum);
/* add carry */
if (z < x)
z++;
return z;
}
static u16
ipsum_calc_block(u16 *x, unsigned len, u16 sum)
ipsum_calc_block(u32 *buf, unsigned len, u16 isum)
{
int rest;
u32 tmp, *xx;
/*
* A few simple facts about the IP checksum (see RFC 1071 for detailed
* discussion):
@ -47,27 +42,17 @@ ipsum_calc_block(u16 *x, unsigned len, u16 sum)
* usual alignment requirements and is reasonably fast.
*/
ASSERT(!(len % 2));
ASSERT(!(len % 4));
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 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;
}