android/dex/EncodedValueCodec.java

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.dex;

import com.android.dex.util.ByteInput;
import com.android.dex.util.ByteOutput;

/**
 * Read and write {@code encoded_value} primitives.
 */
public final class EncodedValueCodec {
    private EncodedValueCodec() {
    }

    /**
     * Writes a signed integral to {@code out}.
     */
    public static void writeSignedIntegralValue(ByteOutput out, int type, long value) {
        /*
         * Figure out how many bits are needed to represent the value,
         * including a sign bit: The bit count is subtracted from 65
         * and not 64 to account for the sign bit. The xor operation
         * has the effect of leaving non-negative values alone and
         * unary complementing negative values (so that a leading zero
         * count always returns a useful number for our present
         * purpose).
         */
        int requiredBits = 65 - Long.numberOfLeadingZeros(value ^ (value >> 63));

        // Round up the requiredBits to a number of bytes.
        int requiredBytes = (requiredBits + 0x07) >> 3;

        /*
         * Write the header byte, which includes the type and
         * requiredBytes - 1.
         */
        out.writeByte(type | ((requiredBytes - 1) << 5));

        // Write the value, per se.
        while (requiredBytes > 0) {
            out.writeByte((byte) value);
            value >>= 8;
            requiredBytes--;
        }
    }

    /**
     * Writes an unsigned integral to {@code out}.
     */
    public static void writeUnsignedIntegralValue(ByteOutput out, int type, long value) {
        // Figure out how many bits are needed to represent the value.
        int requiredBits = 64 - Long.numberOfLeadingZeros(value);
        if (requiredBits == 0) {
            requiredBits = 1;
        }

        // Round up the requiredBits to a number of bytes.
        int requiredBytes = (requiredBits + 0x07) >> 3;

        /*
         * Write the header byte, which includes the type and
         * requiredBytes - 1.
         */
        out.writeByte(type | ((requiredBytes - 1) << 5));

        // Write the value, per se.
        while (requiredBytes > 0) {
            out.writeByte((byte) value);
            value >>= 8;
            requiredBytes--;
        }
    }

    /**
     * Writes a right-zero-extended value to {@code out}.
     */
    public static void writeRightZeroExtendedValue(ByteOutput out, int type, long value) {
        // Figure out how many bits are needed to represent the value.
        int requiredBits = 64 - Long.numberOfTrailingZeros(value);
        if (requiredBits == 0) {
            requiredBits = 1;
        }

        // Round up the requiredBits to a number of bytes.
        int requiredBytes = (requiredBits + 0x07) >> 3;

        // Scootch the first bits to be written down to the low-order bits.
        value >>= 64 - (requiredBytes * 8);

        /*
         * Write the header byte, which includes the type and
         * requiredBytes - 1.
         */
        out.writeByte(type | ((requiredBytes - 1) << 5));

        // Write the value, per se.
        while (requiredBytes > 0) {
            out.writeByte((byte) value);
            value >>= 8;
            requiredBytes--;
        }
    }

    /**
     * Read a signed integer.
     *
     * @param zwidth byte count minus one
     */
    public static int readSignedInt(ByteInput in, int zwidth) {
        int result = 0;
        for (int i = zwidth; i >= 0; i--) {
            result = (result >>> 8) | ((in.readByte() & 0xff) << 24);
        }
        result >>= (3 - zwidth) * 8;
        return result;
    }

    /**
     * Read an unsigned integer.
     *
     * @param zwidth byte count minus one
     * @param fillOnRight true to zero fill on the right; false on the left
     */
    public static int readUnsignedInt(ByteInput in, int zwidth, boolean fillOnRight) {
        int result = 0;
        if (!fillOnRight) {
            for (int i = zwidth; i >= 0; i--) {
                result = (result >>> 8) | ((in.readByte() & 0xff) << 24);
            }
            result >>>= (3 - zwidth) * 8;
        } else {
            for (int i = zwidth; i >= 0; i--) {
                result = (result >>> 8) | ((in.readByte() & 0xff) << 24);
            }
        }
        return result;
    }

    /**
     * Read a signed long.
     *
     * @param zwidth byte count minus one
     */
    public static long readSignedLong(ByteInput in, int zwidth) {
        long result = 0;
        for (int i = zwidth; i >= 0; i--) {
            result = (result >>> 8) | ((in.readByte() & 0xffL) << 56);
        }
        result >>= (7 - zwidth) * 8;
        return result;
    }

    /**
     * Read an unsigned long.
     *
     * @param zwidth byte count minus one
     * @param fillOnRight true to zero fill on the right; false on the left
     */
    public static long readUnsignedLong(ByteInput in, int zwidth, boolean fillOnRight) {
        long result = 0;
        if (!fillOnRight) {
            for (int i = zwidth; i >= 0; i--) {
                result = (result >>> 8) | ((in.readByte() & 0xffL) << 56);
            }
            result >>>= (7 - zwidth) * 8;
        } else {
            for (int i = zwidth; i >= 0; i--) {
                result = (result >>> 8) | ((in.readByte() & 0xffL) << 56);
            }
        }
        return result;
    }
}