compiler-rt/lib/builtins/popcountti2.c

   1 //===-- popcountti2.c - Implement __popcountti2
   2 //----------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements __popcountti2 for the compiler_rt library.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "int_lib.h"
  15
  16 #ifdef CRT_HAS_128BIT
  17
  18 // Returns: count of 1 bits
  19
  20 COMPILER_RT_ABI int __popcountti2(ti_int a) {
  21   tu_int x3 = (tu_int)a;
  22   x3 = x3 - ((x3 >> 1) &
  23              (((tu_int)0x5555555555555555uLL << 64) | 0x5555555555555555uLL));
  24   // Every 2 bits holds the sum of every pair of bits (64)
  25   x3 = ((x3 >> 2) &
  26         (((tu_int)0x3333333333333333uLL << 64) | 0x3333333333333333uLL)) +
  27        (x3 & (((tu_int)0x3333333333333333uLL << 64) | 0x3333333333333333uLL));
  28   // Every 4 bits holds the sum of every 4-set of bits (3 significant bits) (32)
  29   x3 = (x3 + (x3 >> 4)) &
  30        (((tu_int)0x0F0F0F0F0F0F0F0FuLL << 64) | 0x0F0F0F0F0F0F0F0FuLL);
  31   // Every 8 bits holds the sum of every 8-set of bits (4 significant bits) (16)
  32   du_int x2 = (du_int)(x3 + (x3 >> 64));
  33   // Every 8 bits holds the sum of every 8-set of bits (5 significant bits) (8)
  34   su_int x = (su_int)(x2 + (x2 >> 32));
  35   // Every 8 bits holds the sum of every 8-set of bits (6 significant bits) (4)
  36   x = x + (x >> 16);
  37   // Every 8 bits holds the sum of every 8-set of bits (7 significant bits) (2)
  38   //
  39   // Upper 16 bits are garbage
  40   return (x + (x >> 8)) & 0xFF; // (8 significant bits)
  41 }
  42
  43 #endif // CRT_HAS_128BIT