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      1 /* ===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===
      2  *
      3  *                     The LLVM Compiler Infrastructure
      4  *
      5  * This file is dual licensed under the MIT and the University of Illinois Open
      6  * Source Licenses. See LICENSE.TXT for details.
      7  *
      8  * ===----------------------------------------------------------------------===
      9  *
     10  * This file implements __popcountsi2 for the compiler_rt library.
     11  *
     12  * ===----------------------------------------------------------------------===
     13  */
     14 
     15 #include "int_lib.h"
     16 
     17 /* Returns: count of 1 bits */
     18 
     19 COMPILER_RT_ABI si_int
     20 __popcountsi2(si_int a)
     21 {
     22     su_int x = (su_int)a;
     23     x = x - ((x >> 1) & 0x55555555);
     24     /* Every 2 bits holds the sum of every pair of bits */
     25     x = ((x >> 2) & 0x33333333) + (x & 0x33333333);
     26     /* Every 4 bits holds the sum of every 4-set of bits (3 significant bits) */
     27     x = (x + (x >> 4)) & 0x0F0F0F0F;
     28     /* Every 8 bits holds the sum of every 8-set of bits (4 significant bits) */
     29     x = (x + (x >> 16));
     30     /* The lower 16 bits hold two 8 bit sums (5 significant bits).*/
     31     /*    Upper 16 bits are garbage */
     32     return (x + (x >> 8)) & 0x0000003F;  /* (6 significant bits) */
     33 }
     34