/*

 * Copyright (c) 1997, 2019, 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

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 */

#ifndef SHARE_CODE_COMPRESSEDSTREAM_HPP

#define SHARE_CODE_COMPRESSEDSTREAM_HPP

#include "memory/allocation.hpp"

// Simple interface for filing out and filing in basic types

// Used for writing out and reading in debugging information.

class CompressedStream : public ResourceObj {

  friend class VMStructs;

 protected:

  u_char* _buffer;

  int     _position;

  enum {

    // Constants for UNSIGNED5 coding of Pack200

    lg_H = 6, H = 1<<lg_H,    // number of high codes (64)

    L = (1<<BitsPerByte)-H,   // number of low codes (192)

    MAX_i = 4                 // bytes are numbered in (0..4), max 5 bytes

  };

  // 32-bit one-to-one sign encoding taken from Pack200

  // converts leading sign bits into leading zeroes with trailing sign bit

  static juint encode_sign(jint  value) { return (value << 1) ^ (value >> 31); }

  static jint  decode_sign(juint value) { return (value >> 1) ^ -(jint)(value & 1); }

  static juint reverse_int(juint i);   // to trim trailing float 0's

 public:

  CompressedStream(u_char* buffer, int position = 0) {

    _buffer   = buffer;

    _position = position;

  }

  u_char* buffer() const               { return _buffer; }

  // Positioning

  int position() const                 { return _position; }

  void set_position(int position)      { _position = position; }

};

class CompressedReadStream : public CompressedStream {

 private:

  inline u_char read()                 { return _buffer[_position++]; }

  // This encoding, called UNSIGNED5, is taken from J2SE Pack200.

  // It assumes that most values have lots of leading zeroes.

  // Very small values, in the range [0..191], code in one byte.

  // Any 32-bit value (including negatives) can be coded, in

  // up to five bytes.  The grammar is:

  //    low_byte  = [0..191]

  //    high_byte = [192..255]

  //    any_byte  = low_byte | high_byte

  //    coding = low_byte

  //           | high_byte low_byte

  //           | high_byte high_byte low_byte

  //           | high_byte high_byte high_byte low_byte

  //           | high_byte high_byte high_byte high_byte any_byte

  // Each high_byte contributes six bits of payload.

  // The encoding is one-to-one (except for integer overflow)

  // and easy to parse and unparse.

  jint read_int_mb(jint b0) {

    int     pos = position() - 1;

    u_char* buf = buffer() + pos;

    assert(buf[0] == b0 && b0 >= L, "correctly called");

    jint    sum = b0;

    // must collect more bytes:  b[1]...b[4]

    int lg_H_i = lg_H;

    for (int i = 0; ; ) {

      jint b_i = buf[++i]; // b_i = read(); ++i;

      sum += b_i << lg_H_i;  // sum += b[i]*(64**i)

      if (b_i < L || i == MAX_i) {

        set_position(pos+i+1);

        return sum;

      }

      lg_H_i += lg_H;

    }

  }

 public:

  CompressedReadStream(u_char* buffer, int position = 0)

  : CompressedStream(buffer, position) {}

  jboolean read_bool()                 { return (jboolean) read();      }

  jbyte    read_byte()                 { return (jbyte   ) read();      }

  jchar    read_char()                 { return (jchar   ) read_int();  }

  jshort   read_short()                { return (jshort  ) read_signed_int(); }

  jint     read_int()                  { jint   b0 = read();

                                         if (b0 < L)  return b0;

                                         else         return read_int_mb(b0);

                                       }

  jint     read_signed_int();

  jfloat   read_float();               // jfloat_cast(reverse_int(read_int()))

  jdouble  read_double();              // jdouble_cast(2*reverse_int(read_int))

  jlong    read_long();                // jlong_from(2*read_signed_int())

};

class CompressedWriteStream : public CompressedStream {

 private:

  bool full() {

    return _position >= _size;

  }

  void store(u_char b) {

    _buffer[_position++] = b;

  }

  void write(u_char b) {

    if (full()) grow();

    store(b);

  }

  void grow();

  // UNSIGNED5 coding, 1-5 byte cases

  void write_int_mb(jint value) {

    juint sum = value;

    for (int i = 0; ; ) {

      if (sum < L || i == MAX_i) {

        // remainder is either a "low code" or the 5th byte

        assert(sum == (u_char)sum, "valid byte");

        write((u_char)sum);

        break;

      }

      sum -= L;

      int b_i = L + (sum % H);  // this is a "high code"

      sum >>= lg_H;             // extracted 6 bits

      write(b_i); ++i;

    }

  }

 protected:

  int _size;

 public:

  CompressedWriteStream(int initial_size);

  CompressedWriteStream(u_char* buffer, int initial_size, int position = 0)

  : CompressedStream(buffer, position) { _size = initial_size; }

  void write_bool(jboolean value)      { write(value);      }

  void write_byte(jbyte value)         { write(value);      }

  void write_char(jchar value)         { write_int(value); }

  void write_short(jshort value)       { write_signed_int(value);  }

  void write_int(jint value)           { if ((juint)value < L && !full())

                                               store((u_char)value);

                                         else  write_int_mb(value);  }

  void write_signed_int(jint value)    { write_int(encode_sign(value)); }

  void write_float(jfloat value);      // write_int(reverse_int(jint_cast(v)))

  void write_double(jdouble value);    // write_int(reverse_int(<low,high>))

  void write_long(jlong value);        // write_signed_int(<low,high>)

};

#endif // SHARE_CODE_COMPRESSEDSTREAM_HPP