/* * Copyright (c) 1982, 1986 Regents of the University of California. * All rights reserved. The Berkeley software License Agreement * specifies the terms and conditions for redistribution. * * @(#)in_cksum.c 7.1 (Berkeley) 6/5/86 */ #include "types.h" #include "mbuf.h" #include "../netinet/in.h" #include "../netinet/in_systm.h" /* * Checksum routine for Internet Protocol family headers (VAX Version). * * This routine is very heavily used in the network * code and should be modified for each CPU to be as fast as possible. */ in_cksum(m, len) register struct mbuf *m; register int len; { register u_short *w; /* on vax, known to be r9 */ register int sum = 0; /* on vax, known to be r8 */ register int mlen = 0; for (;;) { /* * Each trip around loop adds in * word from one mbuf segment. */ w = mtod(m, u_short *); if (mlen == -1) { /* * There is a byte left from the last segment; * add it into the checksum. Don't have to worry * about a carry-out here because we make sure * that high part of (32 bit) sum is small below. */ sum += *(u_char *)w << 8; w = (u_short *)((char *)w + 1); mlen = m->m_len - 1; len--; } else mlen = m->m_len; m = m->m_next; if (len < mlen) mlen = len; len -= mlen; /* * Force to long boundary so we do longword aligned * memory operations. It is too hard to do byte * adjustment, do only word adjustment. */ if (((int)w&0x2) && mlen >= 2) { sum += *w++; mlen -= 2; } /* * 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. * * We can do a 16 bit ones complement sum 32 bits at a time * because the 32 bit register is acting as two 16 bit * registers for adding, with carries from the low added * into the high (by normal carry-chaining) and carries * from the high carried into the low on the next word * by use of the adwc instruction. This lets us run * this loop at almost memory speed. * * Here there is the danger of high order carry out, and * we carefully use adwc. */ while ((mlen -= 32) >= 0) { #undef ADD #ifdef unneeded /* The loop construct clears carry for us... */ asm("bicpsr $1"); /* clears carry */ #endif #define ADD asm("adwc (r9)+,r8;"); ADD; ADD; ADD; ADD; ADD; ADD; ADD; ADD; asm("adwc $0,r8"); } mlen += 32; while ((mlen -= 8) >= 0) { #ifdef unneeded /* The loop construct clears carry for us... */ asm("bicpsr $1"); /* clears carry */ #endif ADD; ADD; asm("adwc $0,r8"); } mlen += 8; /* * Now eliminate the possibility of carry-out's by * folding back to a 16 bit number (adding high and * low parts together.) Then mop up trailing words * and maybe an odd byte. */ { asm("ashl $-16,r8,r0; addw2 r0,r8"); asm("adwc $0,r8; movzwl r8,r8"); } while ((mlen -= 2) >= 0) { asm("movzwl (r9)+,r0; addl2 r0,r8"); } if (mlen == -1) { sum += *(u_char *)w; } if (len == 0) break; /* * Locate the next block with some data. * If there is a word split across a boundary we * will wrap to the top with mlen == -1 and * then add it in shifted appropriately. */ for (;;) { if (m == 0) { printf("cksum: out of data\n"); goto done; } if (m->m_len) break; m = m->m_next; } } done: /* * Add together high and low parts of sum * and carry to get cksum. * Have to be careful to not drop the last * carry here. */ { asm("ashl $-16,r8,r0; addw2 r0,r8; adwc $0,r8"); asm("mcoml r8,r8; movzwl r8,r8"); } return (sum); }