| /* |
| * Copyright (c) 2013, 2015, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| package org.graalvm.compiler.replacements.aarch64; |
| |
| import org.graalvm.compiler.api.replacements.ClassSubstitution; |
| import org.graalvm.compiler.api.replacements.MethodSubstitution; |
| |
| /** |
| * AArch64 ISA offers a count leading zeros instruction which can be used to implement |
| * numberOfLeadingZeros more efficiently than using BitScanReverse. |
| */ |
| @ClassSubstitution(Integer.class) |
| public class AArch64IntegerSubstitutions { |
| |
| @MethodSubstitution |
| public static int bitCount(int value) { |
| // Based on Warren, Hacker's Delight, slightly adapted to profit from Aarch64 add + shift |
| // instruction. |
| // Assuming the peephole optimizer optimizes all x - y >>> z into a single instruction |
| // this takes 10 instructions. |
| int x = value; |
| x = x - ((x & 0xaaaaaaaa) >>> 1); |
| x = (x & 0x33333333) + ((x & 0xcccccccc) >>> 2); |
| x = (x + (x >>> 4)) & 0x0f0f0f0f; |
| x = x + (x >>> 8); |
| x = x + (x >>> 16); |
| return x & 0x3f; |
| } |
| } |
