helpers.c

#include <stdarg.h>
#include <stdio.h>

#include <stdlib.h>
#include <stdint.h>

static int max(int a, int b) { return a > b ? a : b; }

int print( char* dst, int *dstPos, int dstSize, const char* fmt, ...)
{
	va_list argp;
	va_start(argp, fmt);    
	
	int nChars = vsnprintf( dst ? &dst[*dstPos] : NULL, 
	                     dst? max(dstSize - *dstPos, 0) : 0, 
	                     fmt, argp);
    va_end(argp);
    
    *dstPos += nChars;
        
    return nChars;
}




static char encoding_table[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
                                'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
                                'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
                                'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
                                'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
                                'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
                                'w', 'x', 'y', 'z', '0', '1', '2', '3',
                                '4', '5', '6', '7', '8', '9', '+', '/'};
//static char *decoding_table = NULL;
static int mod_table[] = {0, 2, 1};

char *base64_encode(const unsigned char *data, size_t input_length) {

    int output_length = 4 * ((input_length + 2) / 3);

    char *encoded_data = malloc(output_length + 1);
    if (encoded_data == NULL) return NULL;

    for (uint32_t i = 0, j = 0; i < input_length;) {

        uint32_t octet_a = i < input_length ? (unsigned char)data[i++] : 0;
        uint32_t octet_b = i < input_length ? (unsigned char)data[i++] : 0;
        uint32_t octet_c = i < input_length ? (unsigned char)data[i++] : 0;

        uint32_t triple = (octet_a << 0x10) + (octet_b << 0x08) + octet_c;

        encoded_data[j++] = encoding_table[(triple >> 3 * 6) & 0x3F];
        encoded_data[j++] = encoding_table[(triple >> 2 * 6) & 0x3F];
        encoded_data[j++] = encoding_table[(triple >> 1 * 6) & 0x3F];
        encoded_data[j++] = encoding_table[(triple >> 0 * 6) & 0x3F];
    }

    for (int i = 0; i < mod_table[input_length % 3]; i++)
        encoded_data[output_length - 1 - i] = '=';
        
    encoded_data[output_length] = '\0';

    return encoded_data;
}