hexify: a tiny function which converts binary data into hex. styled after snprintf.

README.md

Blog 2015/9/26

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hexify.c: a snprintf-styled function for turning data into hex

I liked this implementation of a hexification algorithm, so I wrapped it up into a function (styled after the snprintf interface).

$ gcc hexify.c 
$ ./a.out 

test 1
buff: , bytes_written: 0

test 2
buff: , bytes_written: 0

test 3
buff: fe, bytes_written: 2

test 4
buff: fefd, bytes_written: 4

test 5
buff: fcfb, bytes_written: 4

hexify.c

// inspired by http://stackoverflow.com/a/12839870/558735

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

int hexify(uint8_t *in, size_t in_size, char *out, size_t out_size)
{
    if (in_size == 0 || out_size == 0) return 0;

    char map[16+1] = "0123456789abcdef";

    int bytes_written = 0;
    size_t i = 0;
    while(i < in_size && (i*2 + (2+1)) <= out_size)
    {
        uint8_t high_nibble = (in[i] & 0xF0) >> 4;
        *out = map[high_nibble];
        out++;

        uint8_t low_nibble = in[i] & 0x0F;
        *out = map[low_nibble];
        out++;

        i++;

        bytes_written += 2;
    }
    *out = '\0';

    return bytes_written;
}

int main()
{
    int testnum = 0;

    {
        testnum++;
        printf("\ntest %i\n", testnum);
        uint8_t bytes[1] = {254};
        char buff[1];
        int bytes_written = hexify(bytes, sizeof(bytes), buff, sizeof(buff));
        printf("buff: %s, bytes_written: %i\n", buff, bytes_written);
    }

    {
        testnum++;
        printf("\ntest %i\n", testnum);
        uint8_t bytes[1] = {254};
        char buff[2];
        int bytes_written = hexify(bytes, sizeof(bytes), buff, sizeof(buff));
        printf("buff: %s, bytes_written: %i\n", buff, bytes_written);
    }

    {
        testnum++;
        printf("\ntest %i\n", testnum);
        uint8_t bytes[1] = {254};
        char buff[2+1];
        int bytes_written = hexify(bytes, sizeof(bytes), buff, sizeof(buff));
        printf("buff: %s, bytes_written: %i\n", buff, bytes_written);
    }

    {
        testnum++;
        printf("\ntest %i\n", testnum);
        uint8_t bytes[2] = {254, 253};
        char buff[4+1];
        int bytes_written = hexify(bytes, sizeof(bytes), buff, sizeof(buff));
        printf("buff: %s, bytes_written: %i\n", buff, bytes_written);
    }

    {
        testnum++;
        printf("\ntest %i\n", testnum);
        uint8_t bytes[3] = {252, 251, 250};
        char buff[4+1];
        int bytes_written = hexify(bytes, sizeof(bytes), buff, sizeof(buff));
        printf("buff: %s, bytes_written: %i\n", buff, bytes_written);
    }

    return 0;
}