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HdrHistogram supports the recording and analyzing sampled data value counts across a configurable integer value range with configurable value precision within the range. Value precision is expressed as the number of significant digits in the value recording, and provides control over value quantization behavior across the value range and the subsequent value resolution at any given level.
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/**
 * Written by Gil Tene of Azul Systems, and released to the public domain,
 * as explained at http://creativecommons.org/publicdomain/zero/1.0/
 *
 * @author Gil Tene
 */

package org.HdrHistogram;

import java.nio.ByteBuffer;

/**
 * This class provides encoding and decoding methods for writing and reading
 * ZigZag-encoded LEB128-64b9B-variant (Little Endian Base 128) values to/from a
 * {@link ByteBuffer}. LEB128's variable length encoding provides for using a
 * smaller number of bytes for smaller values, and the use of ZigZag encoding
 * allows small (closer to zero) negative values to use fewer bytes. Details
 * on both LEB128 and ZigZag can be readily found elsewhere.
 *
 * The LEB128-64b9B-variant encoding used here diverges from the "original"
 * LEB128 as it extends to 64 bit values: In the original LEB128, a 64 bit
 * value can take up to 10 bytes in the stream, where this variant's encoding
 * of a 64 bit values will max out at 9 bytes.
 *
 * As such, this encoder/decoder should NOT be used for encoding or decoding
 * "standard" LEB128 formats (e.g. Google Protocol Buffers).
 */
class ZigZagEncoding {

    /**
     * Writes a long value to the given buffer in LEB128 ZigZag encoded format
     * @param buffer the buffer to write to
     * @param value  the value to write to the buffer
     */
    static void putLong(ByteBuffer buffer, long value) {
        value = (value << 1) ^ (value >> 63);
        if (value >>> 7 == 0) {
            buffer.put((byte) value);
        } else {
            buffer.put((byte) ((value & 0x7F) | 0x80));
            if (value >>> 14 == 0) {
                buffer.put((byte) (value >>> 7));
            } else {
                buffer.put((byte) (value >>> 7 | 0x80));
                if (value >>> 21 == 0) {
                    buffer.put((byte) (value >>> 14));
                } else {
                    buffer.put((byte) (value >>> 14 | 0x80));
                    if (value >>> 28 == 0) {
                        buffer.put((byte) (value >>> 21));
                    } else {
                        buffer.put((byte) (value >>> 21 | 0x80));
                        if (value >>> 35 == 0) {
                            buffer.put((byte) (value >>> 28));
                        } else {
                            buffer.put((byte) (value >>> 28 | 0x80));
                            if (value >>> 42 == 0) {
                                buffer.put((byte) (value >>> 35));
                            } else {
                                buffer.put((byte) (value >>> 35 | 0x80));
                                if (value >>> 49 == 0) {
                                    buffer.put((byte) (value >>> 42));
                                } else {
                                    buffer.put((byte) (value >>> 42 | 0x80));
                                    if (value >>> 56 == 0) {
                                        buffer.put((byte) (value >>> 49));
                                    } else {
                                        buffer.put((byte) (value >>> 49 | 0x80));
                                        buffer.put((byte) (value >>> 56));
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    }

    /**
     * Writes an int value to the given buffer in LEB128-64b9B ZigZag encoded format
     * @param buffer the buffer to write to
     * @param value  the value to write to the buffer
     */
    static void putInt(ByteBuffer buffer, int value) {
        value = (value << 1) ^ (value >> 31);
        if (value >>> 7 == 0) {
            buffer.put((byte) value);
        } else {
            buffer.put((byte) ((value & 0x7F) | 0x80));
            if (value >>> 14 == 0) {
                buffer.put((byte) (value >>> 7));
            } else {
                buffer.put((byte) (value >>> 7 | 0x80));
                if (value >>> 21 == 0) {
                    buffer.put((byte) (value >>> 14));
                } else {
                    buffer.put((byte) (value >>> 14 | 0x80));
                    if (value >>> 28 == 0) {
                        buffer.put((byte) (value >>> 21));
                    } else {
                        buffer.put((byte) (value >>> 21 | 0x80));
                        buffer.put((byte) (value >>> 28));
                    }
                }
            }
        }
    }

    /**
     * Read an LEB128-64b9B ZigZag encoded long value from the given buffer
     * @param buffer the buffer to read from
     * @return the value read from the buffer
     */
    static long getLong(ByteBuffer buffer) {
        long v = buffer.get();
        long value = v & 0x7F;
        if ((v & 0x80) != 0) {
            v = buffer.get();
            value |= (v & 0x7F) << 7;
            if ((v & 0x80) != 0) {
                v = buffer.get();
                value |= (v & 0x7F) << 14;
                if ((v & 0x80) != 0) {
                    v = buffer.get();
                    value |= (v & 0x7F) << 21;
                    if ((v & 0x80) != 0) {
                        v = buffer.get();
                        value |= (v & 0x7F) << 28;
                        if ((v & 0x80) != 0) {
                            v = buffer.get();
                            value |= (v & 0x7F) << 35;
                            if ((v & 0x80) != 0) {
                                v = buffer.get();
                                value |= (v & 0x7F) << 42;
                                if ((v & 0x80) != 0) {
                                    v = buffer.get();
                                    value |= (v & 0x7F) << 49;
                                    if ((v & 0x80) != 0) {
                                        v = buffer.get();
                                        value |= v << 56;
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
        value = (value >>> 1) ^ (-(value & 1));
        return value;
    }

    /**
     * Read an LEB128-64b9B ZigZag encoded int value from the given buffer
     * @param buffer the buffer to read from
     * @return the value read from the buffer
     */
    static int getInt (ByteBuffer buffer) {
        int v = buffer.get();
        int value = v & 0x7F;
        if ((v & 0x80) != 0) {
            v = buffer.get();
            value |= (v & 0x7F) << 7;
            if ((v & 0x80) != 0) {
                v = buffer.get();
                value |= (v & 0x7F) << 14;
                if ((v & 0x80) != 0) {
                    v = buffer.get();
                    value |= (v & 0x7F) << 21;
                    if ((v & 0x80) != 0) {
                        v = buffer.get();
                        value |= (v & 0x7F) << 28;
                    }
                }
            }
        }
        value = (value >>> 1) ^ (-(value & 1));
        return value;
    }
}