Question

I am studying bitwise operations.

but, I do not understand why they claimed the code is run in parallel.

Compute parity in parallel

unsigned int v;  // word value to compute the parity of
v ^= v >> 16;
v ^= v >> 8;
v ^= v >> 4;
v &= 0xf;
return (0x6996 >> v) & 1;

I copied the code from
http://graphics.stanford.edu/~seander/bithacks.html#ParityParallel

Any help will be appreciated.

Answer 1

A naive, sequential method to compute the parity of a 32-bit word would take (order of) 32 operations. This method is parallel (or “vectorized”) because it operates on many bits at once. The first line v ^= v >> 16 combines the 16 high bits with the 16 low bits in just one instruction.