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