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Last change
on this file since 3626 was 3233, checked in by Bruno Cornec, 12 years ago |
- mindi-busybox 1.21.1 is now complete and builds
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-
Property svn:eol-style
set to
native
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File size:
867 bytes
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| 1 | /*
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| 2 | * Checksum routine for Internet Protocol family headers (C Version)
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| 3 | *
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| 4 | * Licensed under GPLv2, see file LICENSE in this source tree.
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| 5 | */
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| 6 |
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| 7 | #include "libbb.h"
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| 8 |
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| 9 | uint16_t FAST_FUNC inet_cksum(uint16_t *addr, int nleft)
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| 10 | {
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| 11 | /*
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| 12 | * Our algorithm is simple, using a 32 bit accumulator,
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| 13 | * we add sequential 16 bit words to it, and at the end, fold
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| 14 | * back all the carry bits from the top 16 bits into the lower
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| 15 | * 16 bits.
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| 16 | */
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| 17 | unsigned sum = 0;
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| 18 | while (nleft > 1) {
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| 19 | sum += *addr++;
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| 20 | nleft -= 2;
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| 21 | }
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| 22 |
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| 23 | /* Mop up an odd byte, if necessary */
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| 24 | if (nleft == 1) {
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| 25 | if (BB_LITTLE_ENDIAN)
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| 26 | sum += *(uint8_t*)addr;
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| 27 | else
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| 28 | sum += *(uint8_t*)addr << 8;
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| 29 | }
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| 30 |
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| 31 | /* Add back carry outs from top 16 bits to low 16 bits */
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| 32 | sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */
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| 33 | sum += (sum >> 16); /* add carry */
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| 34 |
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| 35 | return (uint16_t)~sum;
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| 36 | }
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