src/java.base/share/classes/jdk/internal/util/HexDigits.java - master - githubmirror/jdk22

src/java.base/share/classes/jdk/internal/util/HexDigits.java
164 строки5 KB
wenshao
8316426: Optimization for HexFormat.formatHex
12 окт 2023, 16:54
12 окт 2023, 16:549355431
/*
 * Copyright (c) 2023, 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 jdk.internal.util;

import java.lang.invoke.MethodHandle;

import jdk.internal.vm.annotation.Stable;

/**
 * Digits class for hexadecimal digits.
 *
 * @since 21
 */
public final class HexDigits implements Digits {
    /**
     * Each element of the array represents the ascii encoded
     * hex relative to its index, for example:<p>
     * <pre>
     *       0 -> '00' -> '0' | ('0' << 8) -> 0x3030
     *       1 -> '01' -> '0' | ('1' << 8) -> 0x3130
     *       2 -> '02' -> '0' | ('2' << 8) -> 0x3230
     *
     *     ...
     *
     *      10 -> '0a' -> '0' | ('a' << 8) -> 0x6130
     *      11 -> '0b' -> '0' | ('b' << 8) -> 0x6230
     *      12 -> '0c' -> '0' | ('b' << 8) -> 0x6330
     *
     *     ...
     *
     *      26 -> '1a' -> '1' | ('a' << 8) -> 0x6131
     *      27 -> '1b' -> '1' | ('b' << 8) -> 0x6231
     *      28 -> '1c' -> '1' | ('c' << 8) -> 0x6331
     *
     *     ...
     *
     *     253 -> 'fd' -> 'f' | ('d' << 8) -> 0x6466
     *     254 -> 'fe' -> 'f' | ('e' << 8) -> 0x6566
     *     255 -> 'ff' -> 'f' | ('f' << 8) -> 0x6666
     * </pre>
     */
    @Stable
    private static final short[] DIGITS;

    /**
     * Singleton instance of HexDigits.
     */
    public static final Digits INSTANCE = new HexDigits();

    static {
        short[] digits = new short[16 * 16];

        for (int i = 0; i < 16; i++) {
            short lo = (short) (i < 10 ? i + '0' : i - 10 + 'a');

            for (int j = 0; j < 16; j++) {
                short hi = (short) ((j < 10 ? j + '0' : j - 10 + 'a') << 8);
                digits[(i << 4) + j] = (short) (hi | lo);
            }
        }

        DIGITS = digits;
    }

    /**
     * Constructor.
     */
    private HexDigits() {
    }

    /**
     * For values from 0 to 255 return a short encoding a pair of hex ASCII-encoded digit characters in little-endian
     * @param i value to convert
     * @param ucase true uppper case, false lower case
     * @return a short encoding a pair of hex ASCII-encoded digit characters
     */
    public static short digitPair(int i, boolean ucase) {
        /*
         * 0b0100_0000_0100_0000 is a selector that selects letters (1 << 6),
         * uppercase or not, and shifting it right by 1 bit incidentally
         * becomes a bit offset between cases (1 << 5).
         *
         *  ([0-9] & 0b100_0000) >> 1 => 0
         *  ([a-f] & 0b100_0000) >> 1 => 32
         *
         *  [0-9] -  0 => [0-9]
         *  [a-f] - 32 => [A-F]
         */
        short v = DIGITS[i & 0xff];
        return ucase
                ? (short) (v - ((v & 0b0100_0000_0100_0000) >> 1))
                : v;
    }

    /**
     * Return a little-endian packed integer for the 4 ASCII bytes for an input unsigned 2-byte integer.
     * {@code b0} is the most significant byte and {@code b1} is the least significant byte.
     * The integer is passed byte-wise to allow reordering of execution.
     */
    public static int packDigits(int b0, int b1) {
        return DIGITS[b0 & 0xff] | (DIGITS[b1 & 0xff] << 16);
    }

    /**
     * Return a little-endian packed long for the 8 ASCII bytes for an input unsigned 4-byte integer.
     * {@code b0} is the most significant byte and {@code b3} is the least significant byte.
     * The integer is passed byte-wise to allow reordering of execution.
     */
    public static long packDigits(int b0, int b1, int b2, int b3) {
        return DIGITS[b0 & 0xff]
                | (DIGITS[b1 & 0xff] << 16)
                | (((long) DIGITS[b2 & 0xff]) << 32)
                | (((long) DIGITS[b3 & 0xff]) << 48);
    }

    @Override
    public int digits(long value, byte[] buffer, int index,
                      MethodHandle putCharMH) throws Throwable {
        while ((value & ~0xFF) != 0) {
            int digits = DIGITS[(int) (value & 0xFF)];
            value >>>= 8;
            putCharMH.invokeExact(buffer, --index, digits >> 8);
            putCharMH.invokeExact(buffer, --index, digits & 0xFF);
        }

        int digits = DIGITS[(int) (value & 0xFF)];
        putCharMH.invokeExact(buffer, --index, digits >> 8);

        if (0xF < value) {
            putCharMH.invokeExact(buffer, --index, digits & 0xFF);
        }

        return index;
    }

    @Override
    public int size(long value) {
        return value == 0 ? 1 :
                67 - Long.numberOfLeadingZeros(value) >> 2;
    }
}