c - What is CHAR_BIT?

Question

Quoting the code for computing the integer absolute value (abs) without branching from http://graphics.stanford.edu/~seander/bithacks.html:

int v;           // we want to find the absolute value of v
unsigned int r;  // the result goes here 
int const mask = v >> sizeof(int) * CHAR_BIT - 1;

r = (v + mask) ^ mask;

Patented variation:

r = (v ^ mask) - mask;

What is CHAR_BIT and how use it?

Answer 1

CHAR_BIT is the number of bits in char. These days, almost all architectures use 8 bits per byte but it is not the case always. Some older machines used to have 7-bit byte.

It can be found in <limits.h>.