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-rw-r--r--lib/checksum.c154
1 files changed, 154 insertions, 0 deletions
diff --git a/lib/checksum.c b/lib/checksum.c
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+++ b/lib/checksum.c
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+/*
+ * Checksum routine for Internet Protocol family headers (C Version).
+ *
+ * Refer to "Computing the Internet Checksum" by R. Braden, D. Borman and
+ * C. Partridge, Computer Communication Review, Vol. 19, No. 2, April 1989,
+ * pp. 86-101, for additional details on computing this checksum.
+ */
+
+#include <zebra.h>
+#include "checksum.h"
+
+#define add_carry(dst, add) \
+ do { \
+ typeof(dst) _add = (add); \
+ dst += _add; \
+ if (dst < _add) \
+ dst++; \
+ } while (0)
+
+uint16_t in_cksumv(const struct iovec *iov, size_t iov_len)
+{
+ const struct iovec *iov_end;
+ uint32_t sum = 0;
+
+ union {
+ uint8_t bytes[2];
+ uint16_t word;
+ } wordbuf;
+ bool have_oddbyte = false;
+
+ /*
+ * Our algorithm is simple, using a 32-bit accumulator (sum),
+ * we add sequential 16-bit words to it, and at the end, fold back
+ * all the carry bits from the top 16 bits into the lower 16 bits.
+ */
+
+ for (iov_end = iov + iov_len; iov < iov_end; iov++) {
+ const uint8_t *ptr, *end;
+
+ ptr = (const uint8_t *)iov->iov_base;
+ end = ptr + iov->iov_len;
+ if (ptr == end)
+ continue;
+
+ if (have_oddbyte) {
+ have_oddbyte = false;
+ wordbuf.bytes[1] = *ptr++;
+
+ add_carry(sum, wordbuf.word);
+ }
+
+ while (ptr + 8 <= end) {
+ add_carry(sum, *(const uint32_t *)(ptr + 0));
+ add_carry(sum, *(const uint32_t *)(ptr + 4));
+ ptr += 8;
+ }
+
+ while (ptr + 2 <= end) {
+ add_carry(sum, *(const uint16_t *)ptr);
+ ptr += 2;
+ }
+
+ if (ptr + 1 <= end) {
+ wordbuf.bytes[0] = *ptr++;
+ have_oddbyte = true;
+ }
+ }
+
+ /* mop up an odd byte, if necessary */
+ if (have_oddbyte) {
+ wordbuf.bytes[1] = 0;
+ add_carry(sum, wordbuf.word);
+ }
+
+ /*
+ * Add back carry outs from top 16 bits to low 16 bits.
+ */
+
+ sum = (sum >> 16) + (sum & 0xffff); /* add high-16 to low-16 */
+ sum += (sum >> 16); /* add carry */
+ return ~sum;
+}
+
+/* Fletcher Checksum -- Refer to RFC1008. */
+#define MODX 4102U /* 5802 should be fine */
+
+/* To be consistent, offset is 0-based index, rather than the 1-based
+ index required in the specification ISO 8473, Annex C.1 */
+/* calling with offset == FLETCHER_CHECKSUM_VALIDATE will validate the checksum
+ without modifying the buffer; a valid checksum returns 0 */
+uint16_t fletcher_checksum(uint8_t *buffer, const size_t len,
+ const uint16_t offset)
+{
+ uint8_t *p;
+ int x, y, c0, c1;
+ uint16_t checksum = 0;
+ uint16_t *csum;
+ size_t partial_len, i, left = len;
+
+ if (offset != FLETCHER_CHECKSUM_VALIDATE)
+ /* Zero the csum in the packet. */
+ {
+ assert(offset
+ < (len - 1)); /* account for two bytes of checksum */
+ csum = (uint16_t *)(buffer + offset);
+ *(csum) = 0;
+ }
+
+ p = buffer;
+ c0 = 0;
+ c1 = 0;
+
+ while (left != 0) {
+ partial_len = MIN(left, MODX);
+
+ for (i = 0; i < partial_len; i++) {
+ c0 = c0 + *(p++);
+ c1 += c0;
+ }
+
+ c0 = c0 % 255;
+ c1 = c1 % 255;
+
+ left -= partial_len;
+ }
+
+ /* The cast is important, to ensure the mod is taken as a signed value.
+ */
+ x = (int)((len - offset - 1) * c0 - c1) % 255;
+
+ if (x <= 0)
+ x += 255;
+ y = 510 - c0 - x;
+ if (y > 255)
+ y -= 255;
+
+ if (offset == FLETCHER_CHECKSUM_VALIDATE) {
+ checksum = (c1 << 8) + c0;
+ } else {
+ /*
+ * Now we write this to the packet.
+ * We could skip this step too, since the checksum returned
+ * would
+ * be stored into the checksum field by the caller.
+ */
+ buffer[offset] = x;
+ buffer[offset + 1] = y;
+
+ /* Take care of the endian issue */
+ checksum = htons((x << 8) | (y & 0xFF));
+ }
+
+ return checksum;
+}