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indent.py `git ls-files | pcregrep '\.[ch]$' | pcregrep -v '^(ldpd|babeld|nhrpd)/'` Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
120 lines
2.9 KiB
C
120 lines
2.9 KiB
C
/*
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* Checksum routine for Internet Protocol family headers (C Version).
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*
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* Refer to "Computing the Internet Checksum" by R. Braden, D. Borman and
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* C. Partridge, Computer Communication Review, Vol. 19, No. 2, April 1989,
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* pp. 86-101, for additional details on computing this checksum.
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*/
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#include <zebra.h>
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#include "checksum.h"
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int /* return checksum in low-order 16 bits */
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in_cksum(void *parg, int nbytes)
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{
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u_short *ptr = parg;
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register long sum; /* assumes long == 32 bits */
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u_short oddbyte;
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register u_short answer; /* assumes u_short == 16 bits */
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/*
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* Our algorithm is simple, using a 32-bit accumulator (sum),
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* we add sequential 16-bit words to it, and at the end, fold back
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* all the carry bits from the top 16 bits into the lower 16 bits.
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*/
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sum = 0;
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while (nbytes > 1) {
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sum += *ptr++;
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nbytes -= 2;
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}
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/* mop up an odd byte, if necessary */
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if (nbytes == 1) {
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oddbyte = 0; /* make sure top half is zero */
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*((u_char *)&oddbyte) = *(u_char *)ptr; /* one byte only */
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sum += oddbyte;
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}
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/*
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* Add back carry outs from top 16 bits to low 16 bits.
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*/
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sum = (sum >> 16) + (sum & 0xffff); /* add high-16 to low-16 */
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sum += (sum >> 16); /* add carry */
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answer = ~sum; /* ones-complement, then truncate to 16 bits */
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return (answer);
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}
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/* Fletcher Checksum -- Refer to RFC1008. */
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#define MODX 4102U /* 5802 should be fine */
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/* To be consistent, offset is 0-based index, rather than the 1-based
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index required in the specification ISO 8473, Annex C.1 */
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/* calling with offset == FLETCHER_CHECKSUM_VALIDATE will validate the checksum
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without modifying the buffer; a valid checksum returns 0 */
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u_int16_t fletcher_checksum(u_char *buffer, const size_t len,
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const uint16_t offset)
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{
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u_int8_t *p;
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int x, y, c0, c1;
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u_int16_t checksum = 0;
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u_int16_t *csum;
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size_t partial_len, i, left = len;
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if (offset != FLETCHER_CHECKSUM_VALIDATE)
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/* Zero the csum in the packet. */
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{
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assert(offset
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< (len - 1)); /* account for two bytes of checksum */
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csum = (u_int16_t *)(buffer + offset);
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*(csum) = 0;
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}
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p = buffer;
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c0 = 0;
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c1 = 0;
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while (left != 0) {
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partial_len = MIN(left, MODX);
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for (i = 0; i < partial_len; i++) {
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c0 = c0 + *(p++);
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c1 += c0;
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}
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c0 = c0 % 255;
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c1 = c1 % 255;
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left -= partial_len;
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}
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/* The cast is important, to ensure the mod is taken as a signed value.
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*/
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x = (int)((len - offset - 1) * c0 - c1) % 255;
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if (x <= 0)
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x += 255;
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y = 510 - c0 - x;
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if (y > 255)
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y -= 255;
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if (offset == FLETCHER_CHECKSUM_VALIDATE) {
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checksum = (c1 << 8) + c0;
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} else {
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/*
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* Now we write this to the packet.
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* We could skip this step too, since the checksum returned
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* would
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* be stored into the checksum field by the caller.
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*/
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buffer[offset] = x;
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buffer[offset + 1] = y;
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/* Take care of the endian issue */
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checksum = htons((x << 8) | (y & 0xFF));
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}
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return checksum;
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}
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