mirror of
https://github.com/jart/cosmopolitan.git
synced 2025-01-31 03:27:39 +00:00
64 lines
3 KiB
C
64 lines
3 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
|
|
│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi │
|
|
╞══════════════════════════════════════════════════════════════════════════════╡
|
|
│ Copyright 2022 Justine Alexandra Roberts Tunney │
|
|
│ │
|
|
│ Permission to use, copy, modify, and/or distribute this software for │
|
|
│ any purpose with or without fee is hereby granted, provided that the │
|
|
│ above copyright notice and this permission notice appear in all copies. │
|
|
│ │
|
|
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
|
|
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
|
|
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
|
|
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
|
|
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
|
|
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
|
|
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
|
|
│ PERFORMANCE OF THIS SOFTWARE. │
|
|
╚─────────────────────────────────────────────────────────────────────────────*/
|
|
#include "libc/intrin/bsr.h"
|
|
#include "libc/macros.h"
|
|
|
|
/**
|
|
* Fingers IP+TCP SYN packet.
|
|
*
|
|
* This returns a hash-like magic number that reflects the SYN packet
|
|
* structure, e.g. ordering of options, maximum segment size, etc.
|
|
*/
|
|
uint32_t FingerSyn(const char *p, size_t n) {
|
|
uint32_t h = 0;
|
|
int i, j, k, iplen, tcplen, ttl;
|
|
if (n >= 20 + 20 && n >= (iplen = (p[0] & 0x0F) * 4) + 20 &&
|
|
n >= iplen + (tcplen = ((p[iplen + 12] & 0xF0) >> 4) * 4)) {
|
|
n = iplen + tcplen;
|
|
// Time to Live
|
|
// ttl<=256 Crisco, Solaris 6
|
|
// ttl<=128 Windows, OpenVMS 8+
|
|
// ttl<=64 Mac, Linux, BSD, Solaris 8+, Tru64, HP-UX
|
|
ttl = p[8] & 255;
|
|
h += bsr(MAX(1, ttl - 1));
|
|
h *= 0x9e3779b1;
|
|
// TCP Options
|
|
// We care about the order and presence of leading common options.
|
|
for (j = 0, i = iplen + 20; i < n; ++j) {
|
|
k = p[i] & 255;
|
|
if (k == 0 || k == 1 || k == 2 || k == 3 || k == 4 || k == 8) {
|
|
if (k <= 1) {
|
|
++i;
|
|
} else if (i + 1 < n) {
|
|
i += p[i + 1] & 255;
|
|
} else {
|
|
break;
|
|
}
|
|
} else {
|
|
break;
|
|
}
|
|
h += j << 8 | k;
|
|
h *= 0x9e3779b1;
|
|
}
|
|
if (!h) {
|
|
++h;
|
|
}
|
|
}
|
|
return h;
|
|
}
|