Basic Base64 Encoder

Post date: May 07, 2021 1:23:48 AM

#include <stdio.h>

#include <stdint.h>

char base64[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcedfghijklmnopqrstuvwxyz0123456789-_";

uint32_t conv2base64(uint32_t x)

{

    uint8_t a, b, c, d;

    a = base64[(x >> 18) & 0x3f];

    b = base64[(x >> 12) & 0x3f];

    c = base64[(x >> 6) & 0x3f];

    d = base64[ x & 0x3f];

    return (a<<24) | (b<<16) | (c<<8) | d;

}

// driver code: Checks if 'Man' gives 'TWFu'

void main()

{

    uint32_t x, y;

    uint8_t msg[5];

    x = 'M'<<16 | 'a'<<8 | 'n'; // assemble

    printf("%X\n", x);

    y = conv2base64(a);         // convert

    msg[0] = y>>24;             // extract chars

    msg[1] = y>>16;

    msg[2] = y>>8;

    msg[3] = y;

    msg[4] = 0;

    printf("%s",msg);

}

A more compact driver uses union.

void main()

{

    uint32_t x;

    union Data {

        uint32_t y;

        uint8_t msg[5];

    } data;

    x = 'f'<<16 | 'o'<<8 | 'o'; // assemble

    printf("%X\n", x);

    data.msg[4] = 0;            // string terminator

    data.y = conv2base64(x);    // convert

    printf("%s", data.msg);

}