//===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements __popcountsi2 for the compiler_rt library.
//
//===----------------------------------------------------------------------===//

#include "int_lib.h"

// Returns: count of 1 bits

si_int
__popcountsi2(si_int a)
{
    su_int x = (su_int)a;
    x = x - ((x >> 1) & 0x55555555);
    // Every 2 bits holds the sum of every pair of bits
    x = ((x >> 2) & 0x33333333) + (x & 0x33333333);
    // Every 4 bits holds the sum of every 4-set of bits (3 significant bits)
    x = (x + (x >> 4)) & 0x0F0F0F0F;
    // Every 8 bits holds the sum of every 8-set of bits (4 significant bits)
    x = (x + (x >> 16));
    // The lower 16 bits hold two 8 bit sums (5 significant bits).
    //    Upper 16 bits are garbage
    return (x + (x >> 8)) & 0x0000003F;  // (6 significant bits)
}