BufferMismatch.java

/*
 * Copyright (c) 2017, 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.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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 java.nio;

import jdk.internal.util.ArraysSupport;

/**
 * Mismatch methods for buffers
 */
// 工具类，用于快速比较两个缓冲区内容是否相同，并返回第一个失配元素的索引。比较原理参见ArraysSupport类。
final class BufferMismatch {
    static int mismatch(ByteBuffer a, int aOff, ByteBuffer b, int bOff, int length) {
        int i = 0;
        if(length > 7) {
            if(a.get(aOff) != b.get(bOff))
                return 0;
            i = ArraysSupport.vectorizedMismatch(
                a.base(),
                a.address + aOff,
                b.base(),
                b.address + bOff, length,
                ArraysSupport.LOG2_ARRAY_BYTE_INDEX_SCALE);
            if(i >= 0)
                return i;
            i = length - ~i;
        }
        for(; i < length; i++) {
            if(a.get(aOff + i) != b.get(bOff + i))
                return i;
        }
        return -1;
    }
    
    static int mismatch(CharBuffer a, int aOff, CharBuffer b, int bOff, int length) {
        int i = 0;
        // Ensure only heap or off-heap buffer instances use the vectorized mismatch.
        // If either buffer is a StringCharBuffer (order is null) then the slow path is taken
        if(length > 3 && a.charRegionOrder() == b.charRegionOrder() && a.charRegionOrder() != null && b.charRegionOrder() != null) {
            if(a.get(aOff) != b.get(bOff))
                return 0;
            i = ArraysSupport.vectorizedMismatch(
                a.base(),
                a.address + (aOff << ArraysSupport.LOG2_ARRAY_CHAR_INDEX_SCALE),
                b.base(),
                b.address + (bOff << ArraysSupport.LOG2_ARRAY_CHAR_INDEX_SCALE),
                length,
                ArraysSupport.LOG2_ARRAY_CHAR_INDEX_SCALE);
            if(i >= 0)
                return i;
            i = length - ~i;
        }
        for(; i < length; i++) {
            if(a.get(aOff + i) != b.get(bOff + i))
                return i;
        }
        return -1;
    }
    
    static int mismatch(ShortBuffer a, int aOff, ShortBuffer b, int bOff, int length) {
        int i = 0;
        if(length > 3 && a.order() == b.order()) {
            if(a.get(aOff) != b.get(bOff))
                return 0;
            i = ArraysSupport.vectorizedMismatch(
                a.base(),
                a.address + (aOff << ArraysSupport.LOG2_ARRAY_SHORT_INDEX_SCALE),
                b.base(),
                b.address + (bOff << ArraysSupport.LOG2_ARRAY_SHORT_INDEX_SCALE),
                length,
                ArraysSupport.LOG2_ARRAY_SHORT_INDEX_SCALE);
            
            if(i >= 0)
                return i;
            i = length - ~i;
        }
        for(; i < length; i++) {
            if(a.get(aOff + i) != b.get(bOff + i))
                return i;
        }
        return -1;
    }
    
    static int mismatch(IntBuffer a, int aOff, IntBuffer b, int bOff, int length) {
        int i = 0;
        if(length > 1 && a.order() == b.order()) {
            if(a.get(aOff) != b.get(bOff))
                return 0;
            i = ArraysSupport.vectorizedMismatch(
                a.base(),
                a.address + (aOff << ArraysSupport.LOG2_ARRAY_INT_INDEX_SCALE),
                b.base(),
                b.address + (bOff << ArraysSupport.LOG2_ARRAY_INT_INDEX_SCALE),
                length,
                ArraysSupport.LOG2_ARRAY_INT_INDEX_SCALE);
            if(i >= 0)
                return i;
            i = length - ~i;
        }
        for(; i < length; i++) {
            if(a.get(aOff + i) != b.get(bOff + i))
                return i;
        }
        return -1;
    }
    
    static int mismatch(FloatBuffer a, int aOff, FloatBuffer b, int bOff, int length) {
        int i = 0;
        if(length > 1 && a.order() == b.order()) {
            if(Float.floatToRawIntBits(a.get(aOff)) == Float.floatToRawIntBits(b.get(bOff))) {
                i = ArraysSupport.vectorizedMismatch(
                    a.base(),
                    a.address + (aOff << ArraysSupport.LOG2_ARRAY_FLOAT_INDEX_SCALE),
                    b.base(),
                    b.address + (bOff << ArraysSupport.LOG2_ARRAY_FLOAT_INDEX_SCALE),
                    length,
                    ArraysSupport.LOG2_ARRAY_FLOAT_INDEX_SCALE);
            }
            // Mismatched
            if(i >= 0) {
                // Check if mismatch is not associated with two NaN values; and
                // is not associated with +0 and -0
                float av = a.get(aOff + i);
                float bv = b.get(bOff + i);
                if(av != bv && (!Float.isNaN(av) || !Float.isNaN(bv)))
                    return i;
                
                // Fall back to slow mechanism
                // ISSUE: Consider looping over vectorizedMismatch adjusting ranges
                // However, requires that returned value be relative to input ranges
                i++;
            }
            // Matched
            else {
                i = length - ~i;
            }
        }
        for(; i < length; i++) {
            float av = a.get(aOff + i);
            float bv = b.get(bOff + i);
            if(av != bv && (!Float.isNaN(av) || !Float.isNaN(bv)))
                return i;
        }
        return -1;
    }
    
    static int mismatch(LongBuffer a, int aOff, LongBuffer b, int bOff, int length) {
        int i = 0;
        if(length > 0 && a.order() == b.order()) {
            if(a.get(aOff) != b.get(bOff))
                return 0;
            i = ArraysSupport.vectorizedMismatch(
                a.base(),
                a.address + (aOff << ArraysSupport.LOG2_ARRAY_LONG_INDEX_SCALE),
                b.base(),
                b.address + (bOff << ArraysSupport.LOG2_ARRAY_LONG_INDEX_SCALE),
                length,
                ArraysSupport.LOG2_ARRAY_LONG_INDEX_SCALE);
            return i >= 0 ? i : -1;
        }
        for(; i < length; i++) {
            if(a.get(aOff + i) != b.get(bOff + i))
                return i;
        }
        return -1;
    }
    
    static int mismatch(DoubleBuffer a, int aOff, DoubleBuffer b, int bOff, int length) {
        int i = 0;
        if(length > 0 && a.order() == b.order()) {
            if(Double.doubleToRawLongBits(a.get(aOff)) == Double.doubleToRawLongBits(b.get(bOff))) {
                i = ArraysSupport.vectorizedMismatch(
                    a.base(),
                    a.address + (aOff << ArraysSupport.LOG2_ARRAY_DOUBLE_INDEX_SCALE),
                    b.base(),
                    b.address + (bOff << ArraysSupport.LOG2_ARRAY_DOUBLE_INDEX_SCALE),
                    length,
                    ArraysSupport.LOG2_ARRAY_DOUBLE_INDEX_SCALE);
            }
            // Mismatched
            if(i >= 0) {
                // Check if mismatch is not associated with two NaN values; and is not associated with +0 and -0
                double av = a.get(aOff + i);
                double bv = b.get(bOff + i);
                if(av != bv && (!Double.isNaN(av) || !Double.isNaN(bv)))
                    return i;
                
                // Fall back to slow mechanism
                // ISSUE: Consider looping over vectorizedMismatch adjusting ranges
                // However, requires that returned value be relative to input ranges
                i++;
            }
            // Matched
            else {
                return -1;
            }
        }
        for(; i < length; i++) {
            double av = a.get(aOff + i);
            double bv = b.get(bOff + i);
            if(av != bv && (!Double.isNaN(av) || !Double.isNaN(bv)))
                return i;
        }
        return -1;
    }
}