converting base 4 code to letters - c

Question

im working on an assmebler project that i have and i need to translate binary machine code that i have to a "weird" 4 base code for example
if i get binary code like this "0000-10-01-00" i should translate it to "aacba"
00=a
01=b
10=c
11=d
i have managed to translate the code to 4 base code but i dont know how to continue from there or if this is the right way to do it,...
adding my code below
void intToBase4 (unsigned int *num)
{
int d[7];
int j,i=0;
double x=0;
while((*num)>0)
{
d[i]=(*num)%4;
i++;
(*num)=(*num)/4;
}
for(x=0,j=i-1; j>=0; j--)
{
x += d[j]*pow(10,j);
}
(*num)=(unsigned int)x;
}

Answer 1

I've included a little 32-bit to num to letter converter for you to grasp the basics. It works a single "32-bit number" at a time. You could use this as a basis for an array based solution like you have half way done in your example, or change the type to be bigger, or whatever. It should show you roughly what you need to do:
void intToBase4 (uint32_t num, char *outString)
{
// There are 16 digits per num in this example
for(int i=0; i<16; i++)
{
// Grab the lowest 2 bits and convert to a letter.
*outString++ = (num & 0x03) + 'a';
// Shift next 2 bits low
num >>= 2;
}
// NUL terminate string.
*outString = '\0';
}

Answer 2

A bit more universal one:
Usage:
value - value to decode, buff - buff where result string will be stored, numofwrds - number of fields to be decoded, ... fields sizes in bits
example "xxxxyyvvzz": - 4 bits, two bits, two bits, two bits
decode(v, buff, 4, 4, 2, 2, 2);
char dictionary[] = "abcdefghijklmnopqrstuwxyz";
char *decode(unsigned int value, char *buff, int numofwrds, ...)
{
va_list vl;
int *fieldsizes = malloc(sizeof(int) * numofwrds);
int bitsize = 0;
char *result = NULL;
if (fieldsizes != NULL)
{
va_start(vl, numofwrds);
for (int i = 0; i < numofwrds; i++)
{
fieldsizes[i] = va_arg(vl, int);
bitsize += fieldsizes[i];
}
va_end(vl);
for (int i = 0; i < numofwrds; i++)
{
unsigned int mask, offset;
mask = (1 << fieldsizes[i]) - 1;
offset = bitsize - fieldsizes[i];
mask <<= offset;
buff[i] = dictionary[(value & mask) >> offset];
bitsize -= fieldsizes[i];
}
free(fieldsizes);
result = buff;
}
buff[numofwrds] = '\0';
return result;
}