1 files changed, 36 insertions, 18 deletions
diff --git a/src/checksum.h b/src/checksum.h
index d9e6bda..f788ff1 100644
--- a/src/checksum.h
+++ b/src/checksum.h
@@ -1,27 +1,45 @@
+#include <stdarg.h>
 #include <stdint.h>
+#include <stdlib.h>
 
-static inline uint16_t do_csum(const char *buf, unsigned size) {
-    unsigned int sum = 0;
-    unsigned int i;
+// based on code from RFCs 1071 and 1624
 
-    for (i = 0; i < size - 1; i += 2)
-        sum += *(uint16_t *)&buf[i];
-
-    if (size & 1)
-        sum += (uint8_t)buf[i];
+/*
+static inline uint16_t csum_update(const void *ptr, uint16_t new_value, uint16_t wsum) {
+    uint32_t sum = *(uint16_t *)ptr + (~ntohs(*(uint16_t *)&new_value) & 0xffff) + ntohs(wsum);
+    sum = (sum & 0xffff) + (sum >> 16);
+    return htons(sum + (sum >> 16));
+}
 
+static inline uint16_t fold_sum(uint32_t sum) {
     while (sum >> 16)
-        sum = (sum & 0xFFFF) + (sum >> 16);
-
-    return ~sum;
+        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);
+static inline uint16_t do_csum(const void *ptr, size_t len) {
+    uint32_t sum = 0;
+
+    while (len > 1) {
+        sum += *(uint16_t *)ptr++;
+        len -= 2;
+    }
 
-    result += sum;
-    if (sum > result)
-        result += 1;
-    return result;
+    if (len > 0)
+        sum += *(uint8_t *)ptr;
+
+    return ~fold_sum(sum);
+}
+
+static inline uint16_t csum_partial(uint16_t sum, const void *ptr, size_t len, ...) {
+    va_list ap;
+    va_start(ap, len);
+    do {
+        sum = ~fold_sum(~sum + ~do_csum(ptr, len));
+    } while ((ptr = va_arg(ap, const void *)) && (len = va_arg(ap, size_t)));
+    va_end(ap);
+    return sum;
 }
+*/
+
+uint16_t csum_partial(const void *buff, int len, uint16_t wsum);