int cksum(struct mbuf *m, int len) { register uint16_t *w; register int sum = 0; register int mlen = 0; int byte_swapped = 0; union { uint8_t c[2]; uint16_t s; } s_util; union { uint16_t s[2]; uint32_t l; } l_util; if (m->m_len == 0) goto cont; w = mtod(m, uint16_t *); mlen = m->m_len; if (len < mlen) mlen = len; #ifdef DEBUG len -= mlen; #endif /* * Force to even boundary. */ if ((1 & (long) w) && (mlen > 0)) { REDUCE; sum <<= 8; s_util.c[0] = *(uint8_t *)w; w = (uint16_t *)((int8_t *)w + 1); mlen--; byte_swapped = 1; } /* * Unroll the loop to make overhead from * branches &c small. */ while ((mlen -= 32) >= 0) { sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3]; sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7]; sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11]; sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15]; w += 16; } mlen += 32; while ((mlen -= 8) >= 0) { sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3]; w += 4; } mlen += 8; if (mlen == 0 && byte_swapped == 0) goto cont; REDUCE; while ((mlen -= 2) >= 0) { sum += *w++; } if (byte_swapped) { REDUCE; sum <<= 8; if (mlen == -1) { s_util.c[1] = *(uint8_t *)w; sum += s_util.s; mlen = 0; } else mlen = -1; } else if (mlen == -1) s_util.c[0] = *(uint8_t *)w; cont: #ifdef DEBUG if (len) { DEBUG_ERROR((dfd, "cksum: out of data\n")); DEBUG_ERROR((dfd, " len = %d\n", len)); } #endif if (mlen == -1) { /* The last mbuf has odd # of bytes. Follow the standard (the odd byte may be shifted left by 8 bits or not as determined by endian-ness of the machine) */ s_util.c[1] = 0; sum += s_util.s; } REDUCE; return (~sum & 0xffff); }