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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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