Word every 2 bits to symbol - c

Question

I have a function that read a word, bit by bit and change to symbol:
I need help to change it to read every 2 bits and change to symbol.
I don't have an idea for it and I need your help guys
void PrintWeirdBits(word w , char* buf){
word mask = 1<<(BITS_IN_WORD-1);
int i;
for(i=0;i<BITS_IN_WORD;i++){
if(mask & w)
buf[i]='/';
else
buf[i]='.';
mask>>=1;
}
buf[i] = '\0';
}
Needed symbols:
00 - *
01 - #
10 - %
11 - !

Answer 1

Here is my proposal for your issue.
Using a lookup table for the symbol decoding will eliminate the need in if statements.
(I assumed word is an unsigned 16 bits data type)
#define BITS_PER_SIGN 2
#define BITS_PER_SIGN_MSK 3 // decimal 3 is 0b11 in binary --> two bits set
// General define could be:
// ((1u << BITS_PER_SIGN) - 1)
#define INIT_MASK (BITS_PER_SIGN_MSK << (BITS_IN_WORD - BITS_PER_SIGN))
void PrintWeirdBits(word w , char* buf)
{
static const char signs[] = {'*', '#', '%', '!'};
unsigned mask = INIT_MASK;
int i;
int sign_idx;
for(i=0; i < BITS_IN_WORD / BITS_PER_SIGN; i++)
{
// the bits of the sign represent the index in the signs array
// just need to align these bits to start from bit 0
sign_idx = (w & mask) >> (BITS_IN_WORD - (i + 1)*BITS_PER_SIGN);
// store the decoded sign in the buffer
buf[i] = signs[sign_idx];
// update the mask for the next symbol
mask >>= BITS_PER_SIGN;
}
buf[i] = '\0';
}
Here it seems to be working.
With small effort it can be updated to a generic code for any bit width of the symbol as long as it is power of two (1, 2, 4, 8) and smaller that BITS_IN_WORD.

Answer 2

Assuming word is unsigned int or an unsigned integer type.
void PrintWeirdBits(word w , char* buf){
word mask = 3 << (BITS_IN_WORD -2);
int i;
word cmp;
for(i=0;i<BITS_IN_WORD/2;i++){
cmp = (mask & w) >> (BITS_IN_WORD -2 -2i);
if(cmp == 0x00)
{
buf[i]='*';
}
else if (cmp == 0x01)
{
buf[i]='#';
}
else if (cmp == 0x02)
{
buf[i]='%';
}
else
{
buf[i]='!';
}
mask>>=2;
}
buf[i] = '\0';
}
The important part is
cmp = (mask & w) >> (BITS_IN_WORD -2 -2i);
Here mask and the input w is bitwise ANDed and the result is right shifted to get the value in the first two bits. These bits are compared to get the result.