/* * BIRD Library -- IP One-Complement Checksum * * (c) 1999--2000 Martin Mares <mj@ucw.cz> * * Can be freely distributed and used under the terms of the GNU GPL. */ /** * DOC: Miscellaneous functions. */ #include <stdarg.h> #include "nest/bird.h" #include "checksum.h" static inline u32 add32(u32 sum, u32 x) { u32 z = sum + x; // return z + (z < sum); /* add carry */ if (z < x) z++; return z; } static u16 ipsum_calc_block(u32 *buf, uint len, u16 isum) { /* * 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 % 4)); if (!len) 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; } static u16 ipsum_calc(void *frag, uint 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, uint); } return sum; } /** * ipsum_verify - verify an IP checksum * @frag: first packet fragment * @len: length in bytes * * This function verifies whether a given fragmented packet * has correct one's complement checksum as used by the IP * protocol. * * It uses all the clever tricks described in RFC 1071 to speed * up checksum calculation as much as possible. * * Result: 1 if the checksum is correct, 0 else. */ int ipsum_verify(void *frag, uint len, ...) { va_list args; u16 sum; va_start(args, len); sum = ipsum_calc(frag, len, args); va_end(args); return sum == 0xffff; } /** * ipsum_calculate - compute an IP checksum * @frag: first packet fragment * @len: length in bytes * * This function calculates a one's complement checksum of a given fragmented * packet. * * It uses all the clever tricks described in RFC 1071 to speed * up checksum calculation as much as possible. */ u16 ipsum_calculate(void *frag, uint len, ...) { va_list args; u16 sum; va_start(args, len); sum = ipsum_calc(frag, len, args); va_end(args); return 0xffff - sum; }