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+/*********************************************************************
+* Filename: rot-13.c
+* Author: Brad Conte (brad AT bradconte.com)
+* Copyright:
+* Disclaimer: This code is presented "as is" without any guarantees.
+* Details: Implementation of the ROT-13 encryption algorithm.
+ Algorithm specification can be found here:
+ *
+ This implementation uses little endian byte order.
+*********************************************************************/
+
+/*************************** HEADER FILES ***************************/
+#include <string.h>
+#include "rot-13.h"
+
+/*********************** FUNCTION DEFINITIONS ***********************/
+void rot13(char str[])
+{
+ int case_type, idx, len;
+
+ for (idx = 0, len = strlen(str); idx < len; idx++) {
+ // Only process alphabetic characters.
+ if (str[idx] < 'A' || (str[idx] > 'Z' && str[idx] < 'a') || str[idx] > 'z')
+ continue;
+ // Determine if the char is upper or lower case.
+ if (str[idx] >= 'a')
+ case_type = 'a';
+ else
+ case_type = 'A';
+ // Rotate the char's value, ensuring it doesn't accidentally "fall off" the end.
+ str[idx] = (str[idx] + 13) % (case_type + 26);
+ if (str[idx] < 26)
+ str[idx] += case_type;
+ }
+}