1*7c3d14c8STreehugger Robot /* ===-- popcountsi2.c - Implement __popcountsi2 ---------------------------=== 2*7c3d14c8STreehugger Robot * 3*7c3d14c8STreehugger Robot * The LLVM Compiler Infrastructure 4*7c3d14c8STreehugger Robot * 5*7c3d14c8STreehugger Robot * This file is dual licensed under the MIT and the University of Illinois Open 6*7c3d14c8STreehugger Robot * Source Licenses. See LICENSE.TXT for details. 7*7c3d14c8STreehugger Robot * 8*7c3d14c8STreehugger Robot * ===----------------------------------------------------------------------=== 9*7c3d14c8STreehugger Robot * 10*7c3d14c8STreehugger Robot * This file implements __popcountsi2 for the compiler_rt library. 11*7c3d14c8STreehugger Robot * 12*7c3d14c8STreehugger Robot * ===----------------------------------------------------------------------=== 13*7c3d14c8STreehugger Robot */ 14*7c3d14c8STreehugger Robot 15*7c3d14c8STreehugger Robot #include "int_lib.h" 16*7c3d14c8STreehugger Robot 17*7c3d14c8STreehugger Robot /* Returns: count of 1 bits */ 18*7c3d14c8STreehugger Robot 19*7c3d14c8STreehugger Robot COMPILER_RT_ABI si_int __popcountsi2(si_int a)20*7c3d14c8STreehugger Robot__popcountsi2(si_int a) 21*7c3d14c8STreehugger Robot { 22*7c3d14c8STreehugger Robot su_int x = (su_int)a; 23*7c3d14c8STreehugger Robot x = x - ((x >> 1) & 0x55555555); 24*7c3d14c8STreehugger Robot /* Every 2 bits holds the sum of every pair of bits */ 25*7c3d14c8STreehugger Robot x = ((x >> 2) & 0x33333333) + (x & 0x33333333); 26*7c3d14c8STreehugger Robot /* Every 4 bits holds the sum of every 4-set of bits (3 significant bits) */ 27*7c3d14c8STreehugger Robot x = (x + (x >> 4)) & 0x0F0F0F0F; 28*7c3d14c8STreehugger Robot /* Every 8 bits holds the sum of every 8-set of bits (4 significant bits) */ 29*7c3d14c8STreehugger Robot x = (x + (x >> 16)); 30*7c3d14c8STreehugger Robot /* The lower 16 bits hold two 8 bit sums (5 significant bits).*/ 31*7c3d14c8STreehugger Robot /* Upper 16 bits are garbage */ 32*7c3d14c8STreehugger Robot return (x + (x >> 8)) & 0x0000003F; /* (6 significant bits) */ 33*7c3d14c8STreehugger Robot } 34