btox

/*

https://stackoverflow.com/a/53966346/9794932

https://tio.run/##TZDrToQwEIX/9ylOMG6KgqHrbc0Cibd9CeTHAkWarIUsRaubfXbsRY1Nk5n2nMl8M3Ws6nqe33vRoFK9pnW33eNMDxHqXo4K/l1VEYRUkCHIgcCcf6rWRZkhSNjy8ur65nZ1d//w@PS8CdbO@NGJHQeNY4k8QxJCD4UskdkyWlWFzHNWIs9BKUMMKhcsDJGmWJqwQKI35ZocCTkRst5NDUc6qkb0F11OiPoceMNbTHIUr5I3nmcypKs1IW6ot62Q1GZ/5E5GNbWFpTgkEZi5NrCjR3aTGm0UX7xvrdXyMC@6Fh3Xo9oXEudgBs8Jbn1eiGxNZLblS37dtl/iv4a9adLS4HR8kUH04zD24zx/Aw

*/

void btox(char *xp, const char *bb, int n) 
{
    const char xx[]= "0123456789ABCDEF";
    while (--n >= 0) xp[n] = xx[(bb[n>>1] >> ((1 - (n&1)) << 2)) & 0xF];
}

/*****/

#include <stdio.h>

typedef unsigned char uint8;

void main(void) 
{
    uint8 buf[] = {0, 1, 10, 11};
    int n = sizeof buf << 1;
    char hexstr[n + 1];

    btox(hexstr, buf, n);
    hexstr[n] = 0; /* Terminate! */
    printf("%s\n", hexstr);
}