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/*
* Checksum routine for Internet Protocol family headers.
*
* This routine is very heavily used in the network
* code and should be modified for each CPU to be as fast as possible.
*
* This implementation is 386 version.
*
* $Id$
*/
#include <stdio.h> /* for puts */
#undef ADDCARRY
#define ADDCARRY(x) if ((x) > 0xffff) (x) -= 0xffff
#define REDUCE {sum = (sum & 0xffff) + (sum >> 16); ADDCARRY(sum);}
/*
* Thanks to gcc we don't have to guess
* which registers contain sum & w.
*/
#define ADD(n) asm("addl " #n "(%2), %0" : "=r" (sum) : "0" (sum), "r" (w))
#define ADDC(n) asm("adcl " #n "(%2), %0" : "=r" (sum) : "0" (sum), "r" (w))
#define LOAD(n) asm volatile("movb " #n "(%1), %0" : "=r" (junk) : "r" (w))
#define MOP asm("adcl $0, %0" : "=r" (sum) : "0" (sum))
int
in_cksum(m, len)
register struct mbuf *m;
register int len;
{
register u_short *w;
register unsigned sum = 0;
register int mlen = 0;
int byte_swapped = 0;
union { char c[2]; u_short s; } su;
for (;m && len; m = m->m_next) {
if (m->m_len == 0)
continue;
w = mtod(m, u_short *);
if (mlen == -1) {
/*
* The first byte of this mbuf is the continuation
* of a word spanning between this mbuf and the
* last mbuf.
*/
/* su.c[0] is already saved when scanning previous
* mbuf. sum was REDUCEd when we found mlen == -1
*/
su.c[1] = *(u_char *)w;
sum += su.s;
w = (u_short *)((char *)w + 1);
mlen = m->m_len - 1;
len--;
} else
mlen = m->m_len;
if (len < mlen)
mlen = len;
len -= mlen;
/*
* Force to long boundary so we do longword aligned
* memory operations
*/
if (3 & (int) w) {
REDUCE;
if ((1 & (int) w) && (mlen > 0)) {
sum <<= 8;
su.c[0] = *(char *)w;
w = (u_short *)((char *)w + 1);
mlen--;
byte_swapped = 1;
}
if ((2 & (int) w) && (mlen >= 2)) {
sum += *w++;
mlen -= 2;
}
}
/*
* Advance to a 486 cache line boundary.
*/
if (4 & (int) w && mlen >= 4) {
ADD(0);
MOP;
w += 2;
mlen -= 4;
}
if (8 & (int) w && mlen >= 8) {
ADD(0);
ADDC(4);
MOP;
w += 4;
mlen -= 8;
}
/*
* Do as much of the checksum as possible 32 bits at at time.
* In fact, this loop is unrolled to make overhead from
* branches &c small.
*/
mlen -= 1;
while ((mlen -= 32) >= 0) {
u_char junk;
/*
* Add with carry 16 words and fold in the last
* carry by adding a 0 with carry.
*
* The early ADD(16) and the LOAD(32) are to load
* the next 2 cache lines in advance on 486's. The
* 486 has a penalty of 2 clock cycles for loading
* a cache line, plus whatever time the external
* memory takes to load the first word(s) addressed.
* These penalties are unavoidable. Subsequent
* accesses to a cache line being loaded (and to
* other external memory?) are delayed until the
* whole load finishes. These penalties are mostly
* avoided by not accessing external memory for
* 8 cycles after the ADD(16) and 12 cycles after
* the LOAD(32). The loop terminates when mlen
* is initially 33 (not 32) to guaranteed that
* the LOAD(32) is within bounds.
*/
ADD(16);
ADDC(0);
ADDC(4);
ADDC(8);
ADDC(12);
LOAD(32);
ADDC(20);
ADDC(24);
ADDC(28);
MOP;
w += 16;
}
mlen += 32 + 1;
if (mlen >= 32) {
ADD(16);
ADDC(0);
ADDC(4);
ADDC(8);
ADDC(12);
ADDC(20);
ADDC(24);
ADDC(28);
MOP;
w += 16;
mlen -= 32;
}
if (mlen >= 16) {
ADD(0);
ADDC(4);
ADDC(8);
ADDC(12);
MOP;
w += 8;
mlen -= 16;
}
if (mlen >= 8) {
ADD(0);
ADDC(4);
MOP;
w += 4;
mlen -= 8;
}
if (mlen == 0 && byte_swapped == 0)
continue; /* worth 1% maybe ?? */
REDUCE;
while ((mlen -= 2) >= 0) {
sum += *w++;
}
if (byte_swapped) {
sum <<= 8;
byte_swapped = 0;
if (mlen == -1) {
su.c[1] = *(char *)w;
sum += su.s;
mlen = 0;
} else
mlen = -1;
} else if (mlen == -1)
/*
* This mbuf has odd number of bytes.
* There could be a word split betwen
* this mbuf and the next mbuf.
* Save the last byte (to prepend to next mbuf).
*/
su.c[0] = *(char *)w;
}
if (len)
puts("cksum: out of data");
if (mlen == -1) {
/* The last mbuf has odd # of bytes. Follow the
standard (the odd byte is shifted left by 8 bits) */
su.c[1] = 0;
sum += su.s;
}
REDUCE;
return (~sum & 0xffff);
}
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