compiler-rt/lib/builtins/popcountdi2.c

   1 //===-- popcountdi2.c - Implement __popcountdi2 ---------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements __popcountdi2 for the compiler_rt library.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "int_lib.h"
  14
  15 // Returns: count of 1 bits
  16
  17 COMPILER_RT_ABI int __popcountdi2(di_int a) {
  18   du_int x2 = (du_int)a;
  19   x2 = x2 - ((x2 >> 1) & 0x5555555555555555uLL);
  20   // Every 2 bits holds the sum of every pair of bits (32)
  21   x2 = ((x2 >> 2) & 0x3333333333333333uLL) + (x2 & 0x3333333333333333uLL);
  22   // Every 4 bits holds the sum of every 4-set of bits (3 significant bits) (16)
  23   x2 = (x2 + (x2 >> 4)) & 0x0F0F0F0F0F0F0F0FuLL;
  24   // Every 8 bits holds the sum of every 8-set of bits (4 significant bits) (8)
  25   su_int x = (su_int)(x2 + (x2 >> 32));
  26   // The lower 32 bits hold four 16 bit sums (5 significant bits).
  27   //   Upper 32 bits are garbage
  28   x = x + (x >> 16);
  29   // The lower 16 bits hold two 32 bit sums (6 significant bits).
  30   //   Upper 16 bits are garbage
  31   return (x + (x >> 8)) & 0x0000007F; // (7 significant bits)
  32 }