mirror of
https://github.com/jart/cosmopolitan.git
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8bfd56b59e
Now that these functions are behind _COSMO_SOURCE there's no reason for having the ugly underscore anymore. To use these functions, you need to pass -mcosmo to cosmocc.
65 lines
3 KiB
C
65 lines
3 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi │
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2022 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/intrin/bsr.h"
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#include "libc/macros.internal.h"
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/**
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* Fingers IP+TCP SYN packet.
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*
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* This returns a hash-like magic number that reflects the SYN packet
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* structure, e.g. ordering of options, maximum segment size, etc.
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*/
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uint32_t FingerSyn(const char *p, size_t n) {
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uint32_t h = 0;
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int i, j, k, iplen, tcplen, ttl;
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if (n >= 20 + 20 && n >= (iplen = (p[0] & 0x0F) * 4) + 20 &&
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n >= iplen + (tcplen = ((p[iplen + 12] & 0xF0) >> 4) * 4)) {
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n = iplen + tcplen;
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// Time to Live
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// ttl<=256 Crisco, Solaris 6
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// ttl<=128 Windows, OpenVMS 8+
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// ttl<=64 Mac, Linux, BSD, Solaris 8+, Tru64, HP-UX
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ttl = p[8] & 255;
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h += bsr(MAX(1, ttl - 1));
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h *= 0x9e3779b1;
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// TCP Options
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// We care about the order and presence of leading common options.
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for (j = 0, i = iplen + 20; i < n; ++j) {
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k = p[i] & 255;
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if (k == 0 || k == 1 || k == 2 || k == 3 || k == 4 || k == 8) {
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if (k <= 1) {
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++i;
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} else if (i + 1 < n) {
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i += p[i + 1] & 255;
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} else {
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break;
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}
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} else {
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break;
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}
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h += j << 8 | k;
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h *= 0x9e3779b1;
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}
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if (!h) {
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++h;
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}
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}
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return h;
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}
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