diff options
Diffstat (limited to 'usr.sbin/ospfd/iso_cksum.c')
| -rw-r--r-- | usr.sbin/ospfd/iso_cksum.c | 38 |
1 files changed, 24 insertions, 14 deletions
diff --git a/usr.sbin/ospfd/iso_cksum.c b/usr.sbin/ospfd/iso_cksum.c index f3a050b37fe..de8d2c6a156 100644 --- a/usr.sbin/ospfd/iso_cksum.c +++ b/usr.sbin/ospfd/iso_cksum.c @@ -1,4 +1,4 @@ -/* $OpenBSD: iso_cksum.c,v 1.1 2005/01/28 14:05:40 claudio Exp $ */ +/* $OpenBSD: iso_cksum.c,v 1.2 2005/10/12 09:51:58 claudio Exp $ */ /* * Copyright (c) 2005 Claudio Jeker <claudio@openbsd.org> @@ -21,17 +21,18 @@ #include "ospfd.h" #include "log.h" +/* implementation of Fletcher Checksum -- see RFC 1008 for more info */ + /* pos needs to be 0 for verify and 2 <= pos < len for calculation */ u_int16_t iso_cksum(void *buf, u_int16_t len, u_int16_t pos) { u_int8_t *p = buf; - int c0 = 0, c1 = 0; /* counters */ - int r0, r1; /* results */ + int c0 = 0, c1 = 0, x; /* counters */ u_int16_t sop; - sop = len - pos - 1; /* pos is an offset (pos 2 is at len 3) */ - p += 2; + sop = len - pos - 1; /* pos is an offset (pos 2 is 3rd element) */ + p += 2; /* jump over age field */ len -= 2; while (len--) { c0 += *p++; @@ -41,18 +42,27 @@ iso_cksum(void *buf, u_int16_t len, u_int16_t pos) c0 %= 255; c1 %= 255; } +#ifdef DEBUG + if (c0 + 256 < c0 || c1 + 256 < c1) + fatalx("iso_cksum: overflowed"); +#endif } - r0 = c0 = c0 % 255; - r1 = c1 % 255; if (pos) { - r0 = ((sop * r0 - r1)) % 255; - if (r0 <= 0) - r0 += 255; - r1 = 510 - r0 - c0; - if (r1 > 255) - r1 -= 255; + x = ((sop * c0 - c1)) % 255; + if (x <= 0) + x += 255; +#if 1 + c1 = 510 - c0 - x; + if (c1 > 255) + c1 -= 255; +#else + c1 = (-c0 - x) % 255; + if (c1 < 0) + c1 += 255; +#endif + c0 = x; } - return (r0 << 8 | r1); + return (c0 << 8 | c1); } |