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/* ===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===
*
* The LLVM Compiler Infrastructure
*
* This file is dual licensed under the MIT and the University of Illinois Open
* Source Licenses. See LICENSE.TXT for details.
*
* ===----------------------------------------------------------------------===
*
* This file implements __popcountsi2 for the compiler_rt library.
*
* ===----------------------------------------------------------------------===
*/
#include "int_lib.h"
/* Returns: count of 1 bits */
COMPILER_RT_ABI 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) */
}
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