1 /* ===-- popcountdi2.c - Implement __popcountdi2 ----------------------------=== 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 __popcountdi2 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 __popcountdi2(di_int a) 21 { 22 du_int x2 = (du_int)a; 23 x2 = x2 - ((x2 >> 1) & 0x5555555555555555uLL); 24 /* Every 2 bits holds the sum of every pair of bits (32) */ 25 x2 = ((x2 >> 2) & 0x3333333333333333uLL) + (x2 & 0x3333333333333333uLL); 26 /* Every 4 bits holds the sum of every 4-set of bits (3 significant bits) (16) */ 27 x2 = (x2 + (x2 >> 4)) & 0x0F0F0F0F0F0F0F0FuLL; 28 /* Every 8 bits holds the sum of every 8-set of bits (4 significant bits) (8) */ 29 su_int x = (su_int)(x2 + (x2 >> 32)); 30 /* The lower 32 bits hold four 16 bit sums (5 significant bits). */ 31 /* Upper 32 bits are garbage */ 32 x = x + (x >> 16); 33 /* The lower 16 bits hold two 32 bit sums (6 significant bits). */ 34 /* Upper 16 bits are garbage */ 35 return (x + (x >> 8)) & 0x0000007F; /* (7 significant bits) */ 36 } 37
