1 /* 2 * Copyright (c) 2013, 2016, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 */ 23 package org.graalvm.compiler.replacements.aarch64; 24 25 import org.graalvm.compiler.api.replacements.ClassSubstitution; 26 import org.graalvm.compiler.api.replacements.MethodSubstitution; 27 28 /** 29 * Aarch64 ISA offers a count leading zeros instruction which can be used to implement 30 * numberOfLeadingZeros more efficiently than using BitScanReverse. 31 */ 32 @ClassSubstitution(Long.class) 33 public class AArch64LongSubstitutions { 34 35 @MethodSubstitution 36 public static int bitCount(long value) { 37 // Based on Warren, Hacker's Delight, slightly adapted to profit from Aarch64 add + shift 38 // instruction. 39 // Assuming the peephole optimizer optimizes all x - y >>> z into a single instruction 40 // this takes 11 instructions. 41 long x = value; 42 x = x - ((x & 0xaaaaaaaaaaaaaaaaL) >>> 1); 43 x = (x & 0x3333333333333333L) + ((x & 0xccccccccccccccccL) >>> 2); 44 x = (x + (x >>> 4)) & 0x0f0f0f0f0f0f0f0fL; 45 x = x + (x >>> 8); 46 x = x + (x >>> 16); 47 x = x + (x >>> 32); 48 return (int) x & 0x7f; 49 } 50 51 }