72 lines
1.5 KiB
C
72 lines
1.5 KiB
C
/*
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* Filename: crypt.c
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* Authors(s): Roland (r.weirhowell@gmail.com)
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* Description: Perform caesar cipher cryptographic operations
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*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at https://mozilla.org/MPL/2.0/.
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*/
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#include "crypt.h"
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#include <stdbool.h>
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#include <stdint.h>
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/*
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* For built in C mod operator (%) -1 % 26 == -1
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* For the requirements of this algorithm -1 mod 26 == 25 is required
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* The below functions accomplish this
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*/
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// Which of the two below functions is faster (find out!)
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inline int mod(int a, int b)
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{
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return (a % b + b) % b;
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}
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inline int fast_mod(int a, int b)
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{
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const int result = a % b;
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return result >= 0 ? result : result + b;
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}
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/*
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* 65 - 90 = ASCII 'A' - 'Z'
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* 97 - 122 = ASCII 'a' - 'z'
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*/
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inline bool isupper(char c)
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{
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return c >= 'A' && c <= 'Z';
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}
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void caesar_encrypt(char* str, int64_t size, int key)
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{
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for (int64_t i = 0; i < size && str[i] != '\n'; i++)
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if (str[i] != ' ')
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{
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bool upper = isupper(str[i]);
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str[i] += (char)key - (upper ? 65 : 97);
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str[i] %= 26;
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str[i] += (upper ? 65 : 97);
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}
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}
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void caesar_decrypt(char* str, int64_t size, int key)
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{
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for (int64_t i = 0; i < size && str[i] != '\n'; i++)
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if (str[i] != ' ')
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{
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bool upper = isupper(str[i]);
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str[i] = str[i] - (char)key - (upper ? 65 : 97);
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str[i] = (char)mod(str[i], 26);
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str[i] += (upper ? 65 : 97);
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}
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}
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