Add start of checksumming.

1 files changed, 27 insertions, 0 deletions

diff --git a/src/checksum.h b/src/checksum.h
new file mode 100644
index 0000000..d9e6bda
--- /dev/null
+++ b/src/checksum.h
@@ -0,0 +1,27 @@
+#include <stdint.h>
+
+static inline uint16_t do_csum(const char *buf, unsigned size) {
+    unsigned int sum = 0;
+    unsigned int i;
+
+    for (i = 0; i < size - 1; i += 2)
+        sum += *(uint16_t *)&buf[i];
+
+    if (size & 1)
+        sum += (uint8_t)buf[i];
+
+    while (sum >> 16)
+        sum = (sum & 0xFFFF) + (sum >> 16);
+
+    return ~sum;
+}
+
+static inline uint16_t csum_partial(const void *buff, int len, uint16_t wsum) {
+    unsigned int sum = (unsigned int)wsum;
+    unsigned int result = do_csum(buff, len);
+
+    result += sum;
+    if (sum > result)
+        result += 1;
+    return result;
+}