Message Integrity Checking

[uccvend-snackrom.git] / ROM2 / xmodem.c

diff --git a/ROM2/xmodem.c b/ROM2/xmodem.c
index 7615d9b..d0e09dd 100644 (file)
--- a/ROM2/xmodem.c
+++ b/ROM2/xmodem.c
@@ -21,6 +21,7 @@
 #include "chime.h"
 #include "sci.h"
 #include "xmodem.h"
+#include "crctab.h"
 
 /* These definitions are for xmodem protocol. */
 
@@ -51,43 +52,22 @@ readchar (int timeout)
   return 0;
 }
 
-#define CRC16 0x1021           /* Generator polynomial (X^16 + X^12 + X^5 + 1) */
-
-
-/* Call this to init the fast CRC-16 calculation table.  */
-
-static short crctab(u8 val) {
-      int i;
-      unsigned int crc;
-
-      crc = val << 8;
-
-      for (i = 0; i < 8; ++i)
-       {
-         crc <<= 1;
-
-         if (crc & 0x10000)
-           crc ^= CRC16;
-       }
-
-         return crc;
-}
-
 /* Calculate a CRC-16 for the LEN byte message pointed at by P.  */
-/* Pads with ^Z if necessary */
+/* Pads with ^Z up to 128 bytes if told to */
 
-static unsigned short
-docrc (unsigned char *p, int len)
+unsigned short
+docrc (unsigned char *p, short len, bool pad, unsigned short crc)
 {
-  int len2 = len;
-  unsigned short crc = 0;
+  short len2 = len;
 
-  while (len-- > 0)
-    crc = (crc << 8) ^ crctab((crc >> 8) ^ *p++);
-  if (len2 < 128) {
+  while (len-- > 0) {
+    crc = (crc << 8) ^ (crctab[(crc >> 8) ^ *p]);
+       p++;
+  }
+  if (pad && len2 < 128) {
     len = 128-len;
     while (len-- > 0)
-      crc = (crc << 8) ^ crctab((crc >> 8) ^ 0x1a);
+      crc = (crc << 8) ^ crctab[(crc >> 8) ^ 0x1a];
   }
 
   return crc;
@@ -183,7 +163,7 @@ xmodem_send_packet (const unsigned char *packet, int len)
     if (crcflag) {
       u16 crc;
 
-      crc = docrc ((unsigned char*)packet, len);
+      crc = docrc ((unsigned char*)packet, len, 1, 0);
 
       s[0] = crc >> 8;
       s[1] = crc & 0xff;