base69.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "base69.h"



// Base69 alphabet
const char *base69_alphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz+/=@*-!#";

// Reverse a string
void reverseString(char *str) {
    int length = strlen(str);
    int start = 0;
    int end = length - 1;
    while (start < end) {
        char temp = str[start];
        str[start] = str[end];
        str[end] = temp;
        start++;
        end--;
    }
}

// Base69 encoder
void encode_base69(int input, char *output) {
    int remainder;
    int index = 0;
    char tempBuffer[input]; // Assuming a maximum length for the encoded string

    // Add prefix "69*|"
    strcpy(output, "69*|");
    int prefixLength = strlen(output);

    while (input > 0) {
        remainder = input % 70;
        input /= 70;
        tempBuffer[index++] = base69_alphabet[remainder];
    }

    tempBuffer[index] = '\0'; // Null-terminate the temporary buffer
    reverseString(tempBuffer); // Reverse the encoded string

    strcat(output, tempBuffer); // Concatenate the reversed string to the output after the prefix
}

// Base69 decoder
int decode_base69(char *input) {
    int index = 0;
    int output = 0;
    // Skip the prefix "69*|"
    int prefixLength = strlen("69*|");
    input += prefixLength;
    //loop through the input string
    while (*input) {
        //find the index of the current character in the alphabet
        char *position = strchr(base69_alphabet, *input);
        int digit = position - base69_alphabet;
        //convert the digit to base 10
        output = output * 70 + digit;
        input++;
    }

    return output;
}