1 /* ===-- popcountdi2.c - Implement __popcountdi2 ----------------------------===
3 * The LLVM Compiler Infrastructure
5 * This file is dual licensed under the MIT and the University of Illinois Open
6 * Source Licenses. See LICENSE.TXT for details.
8 * ===----------------------------------------------------------------------===
10 * This file implements __popcountdi2 for the compiler_rt library.
12 * ===----------------------------------------------------------------------===
18 /* Returns: count of 1 bits */
20 COMPILER_RT_ABI si_int
21 __popcountdi2(di_int a)
23 du_int x2 = (du_int)a;
24 x2 = x2 - ((x2 >> 1) & 0x5555555555555555uLL);
25 /* Every 2 bits holds the sum of every pair of bits (32) */
26 x2 = ((x2 >> 2) & 0x3333333333333333uLL) + (x2 & 0x3333333333333333uLL);
27 /* Every 4 bits holds the sum of every 4-set of bits (3 significant bits) (16) */
28 x2 = (x2 + (x2 >> 4)) & 0x0F0F0F0F0F0F0F0FuLL;
29 /* Every 8 bits holds the sum of every 8-set of bits (4 significant bits) (8) */
30 su_int x = (su_int)(x2 + (x2 >> 32));
31 /* The lower 32 bits hold four 16 bit sums (5 significant bits). */
32 /* Upper 32 bits are garbage */
34 /* The lower 16 bits hold two 32 bit sums (6 significant bits). */
35 /* Upper 16 bits are garbage */
36 return (x + (x >> 8)) & 0x0000007F; /* (7 significant bits) */