base64 in C language

decode_base64.c

#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <stdbool.h>

int main(void) {
    const uint8_t base64chars[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    uint32_t buf = 0;
    int8_t iter = 0;
    bool enter_loop = true;
    while (enter_loop) {
        int16_t input = getchar();
        uint8_t *p = NULL;

        switch(input) {
            case EOF:
            case '=':
                enter_loop = false;
                continue;
            default:
                p = (uint8_t *)strchr((const char *)base64chars, input);
                if (p == NULL) { continue; }
                uint8_t c = p - base64chars;
                buf = (buf << 6) | c;
                iter += 1;

                if (iter == 4) {
                    for (int_fast8_t i=16; i>=0; i-=8) {
                        putchar((buf >> i) & 255);
                    }
                    iter = buf = 0;
                }
                break;
        }
    }

    switch (iter) {
        case 2:
            putchar((buf >> 4) & 255);
            break;
        case 3:
            for (int_fast8_t i=10; i>=0; i-=8) {
                putchar((buf >> i) & 255);
            }
            break;
    }

    return 0;
}

encode_base64.c

#include <stdio.h>
#include <stdint.h>

int main(void) {
    const uint8_t base64chars[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    uint32_t buf = 0;
    int_fast8_t iter = 0;
    uint_fast8_t len = 0;

    while (1) {
        int16_t input = getchar();

        if (input == EOF) { break; }

        buf = (buf << 8) | ((uint8_t)input & 255);
        iter += 1;

        if (len == 76) {
            printf("%s", "\r\n");
            len = 0;
        }

        if (iter == 3) {
            for (int_fast8_t i=18; i>=0; i-=6) {
                putchar(base64chars[(uint8_t)(buf >> i) & 63]);
            }
            iter = buf = 0;
            len += 4;
        }
    }

    if (iter > 0) {
        uint_fast8_t p = 3 - iter;

        switch (iter) {
            case 1:
                buf <<= 4;
                break;
            case 2:
                buf <<= 2;
                break;
        }

        while (1) {
            putchar(base64chars[(uint8_t)(buf >> (iter*6)) & 63]);
            iter -= 1;
            if (iter < 0) { break; }
        }

        while (1) {
            putchar('=');
            p -= 1;
            if (p == 0) { break; }
        }
    }

    printf("%s", "\r\n");

    return 0;
}