From 8b756e368a33a02d7783053b84bc1e5b50419ff0 Mon Sep 17 00:00:00 2001
From: Jeffrey Armstrong <jeffrey.armstrong@approximatrix.com>
Date: Fri, 9 Oct 2015 10:34:49 -0400
Subject: Initial commit

---
 client/f16.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)
 create mode 100644 client/f16.c

(limited to 'client/f16.c')

diff --git a/client/f16.c b/client/f16.c
new file mode 100644
index 0000000..2fd05f9
--- /dev/null
+++ b/client/f16.c
@@ -0,0 +1,73 @@
+/*       Recursive Walking Backup
+ *       Copyright © 2015 Jeffrey Armstrong <jeff@rainbow-100.com>
+ *       http://jeff.rainbow-100.com/
+ *
+ *       This program is free software: you can redistribute it and/or modify
+ *       it under the terms of the GNU General Public License as published by
+ *       the Free Software Foundation, either version 3 of the License, or
+ *       (at your option) any later version.
+ *       
+ *       This program is distributed in the hope that it will be useful
+ *       but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *       GNU General Public License for more details.
+ *       
+ *       You should have received a copy of the GNU General Public License
+ *       along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/* f16.c - Implementation of a Fletcher 16-bit checksum.  The file also
+ *         contains a simple test program that can be enabled by defining
+ *         TEST_FLETCHER at compile time.
+ */
+
+#include <stdio.h>
+
+/* Computes the Fletcher 16-bit checksum and returns the value in the
+ * b1 and b2 arguments.
+ */
+void fletcher16(unsigned char *data, 
+                int n, 
+                unsigned char *b1, 
+                unsigned char *b2)
+{
+int c1, c2;
+int i;
+int toint;
+
+        c1 = 0; c2 = 0;
+        for(i=0;i<n;i++) {
+            toint = (int)data[i];
+            c1 = (c1 + toint) % 255;
+            c2 = (c2 + c1) % 255;
+        }
+        
+        i = (255 - (c1 + c2) % 255);
+        *b1 = (int)i;
+        *b2 = (char)(255 - (c1 + i) % 255);
+}
+
+#ifdef TEST_FLETCHER
+
+#define TEST_STR        "The IBM PC/XT is inferior"
+int main(int argc, char *argv[])
+{
+char b1, b2;
+FILE *fp;
+char buf[64];
+int i;
+
+        if(argc > 2) {
+                fletcher16(TEST_STR, strlen(TEST_STR), &b1, &b2);
+                printf("Results for '%s': %d, %d\n", TEST_STR, (int)b1, (int)b2);
+        } else {
+                fp = fopen(argv[1], "rb");
+                fread(buf, sizeof(char), 64, fp);
+                fletcher16(buf, 64, &b1, &b2);
+                printf("Results for 1st 64 bytes: %d, %d\n", (int)b1, (int)b2);
+                fclose(fp);
+        }
+        return (int)b1;
+}
+
+#endif
-- 
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