39 lines
898 B
C
39 lines
898 B
C
/*
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* Checksum routine for Internet Protocol family headers (C Version)
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*
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* Licensed under GPLv2, see file LICENSE in this source tree.
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*/
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#include "libbb.h"
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uint16_t FAST_FUNC inet_cksum(const void *ptr, int nleft)
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{
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const uint16_t *addr = ptr;
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/*
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* Our algorithm is simple, using a 32 bit accumulator,
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* we add sequential 16 bit words to it, and at the end, fold
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* back all the carry bits from the top 16 bits into the lower
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* 16 bits.
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*/
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unsigned sum = 0;
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while (nleft > 1) {
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sum += *addr++;
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nleft -= 2;
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}
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/* Mop up an odd byte, if necessary */
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if (nleft == 1) {
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if (BB_LITTLE_ENDIAN)
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sum += *(uint8_t*)addr;
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else
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sum += *(uint8_t*)addr << 8;
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}
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/* Add back carry outs from top 16 bits to low 16 bits */
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sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */
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sum += (sum >> 16); /* add carry */
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return (uint16_t)~sum;
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}
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