I need to compute a number (a/(2**b) using only bitwise operators such as ! & ^ ~ and shifts. I was given the following hint but I'm new to C and I dont know what the code means:
int bias = x>0 ? 0 : ((1<<n)-1);
Can anyone explain it to me?
I thought a>>b would work but I dont think it works for negative numbers.
That particular bit of code gives you a bias of 0 if x is positive. Otherwise it produces a mask of the lower n bits. The x = a ? b : c; pattern is called the ternary operator(technically the 'conditional operator', apparently) in C.
n (1<<n) (1<<n)-1 binary
0 0x01 0x00 00000000
1 0x02 0x01 00000001
2 0x04 0x03 00000011
3 0x08 0x07 00000111
4 0x10 0x0F 00001111
5 0x20 0x1F 00011111
6 0x40 0x3F 00111111
7 0x80 0x7F 01111111
...