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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;
}
}
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