1/*
2 * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
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23 */
24
25#ifndef SHARE_CODE_COMPRESSEDSTREAM_HPP
26#define SHARE_CODE_COMPRESSEDSTREAM_HPP
27
28#include "memory/allocation.hpp"
29
30// Simple interface for filing out and filing in basic types
31// Used for writing out and reading in debugging information.
32
33class CompressedStream : public ResourceObj {
34 friend class VMStructs;
35 protected:
36 u_char* _buffer;
37 int _position;
38
39 enum {
40 // Constants for UNSIGNED5 coding of Pack200
41 lg_H = 6, H = 1<<lg_H, // number of high codes (64)
42 L = (1<<BitsPerByte)-H, // number of low codes (192)
43 MAX_i = 4 // bytes are numbered in (0..4), max 5 bytes
44 };
45
46 // 32-bit one-to-one sign encoding taken from Pack200
47 // converts leading sign bits into leading zeroes with trailing sign bit
48 static juint encode_sign(jint value) { return (value << 1) ^ (value >> 31); }
49 static jint decode_sign(juint value) { return (value >> 1) ^ -(jint)(value & 1); }
50 static juint reverse_int(juint i); // to trim trailing float 0's
51 public:
52 CompressedStream(u_char* buffer, int position = 0) {
53 _buffer = buffer;
54 _position = position;
55 }
56
57 u_char* buffer() const { return _buffer; }
58
59 // Positioning
60 int position() const { return _position; }
61 void set_position(int position) { _position = position; }
62};
63
64
65class CompressedReadStream : public CompressedStream {
66 private:
67 inline u_char read() { return _buffer[_position++]; }
68
69 // This encoding, called UNSIGNED5, is taken from J2SE Pack200.
70 // It assumes that most values have lots of leading zeroes.
71 // Very small values, in the range [0..191], code in one byte.
72 // Any 32-bit value (including negatives) can be coded, in
73 // up to five bytes. The grammar is:
74 // low_byte = [0..191]
75 // high_byte = [192..255]
76 // any_byte = low_byte | high_byte
77 // coding = low_byte
78 // | high_byte low_byte
79 // | high_byte high_byte low_byte
80 // | high_byte high_byte high_byte low_byte
81 // | high_byte high_byte high_byte high_byte any_byte
82 // Each high_byte contributes six bits of payload.
83 // The encoding is one-to-one (except for integer overflow)
84 // and easy to parse and unparse.
85
86 jint read_int_mb(jint b0) {
87 int pos = position() - 1;
88 u_char* buf = buffer() + pos;
89 assert(buf[0] == b0 && b0 >= L, "correctly called");
90 jint sum = b0;
91 // must collect more bytes: b[1]...b[4]
92 int lg_H_i = lg_H;
93 for (int i = 0; ; ) {
94 jint b_i = buf[++i]; // b_i = read(); ++i;
95 sum += b_i << lg_H_i; // sum += b[i]*(64**i)
96 if (b_i < L || i == MAX_i) {
97 set_position(pos+i+1);
98 return sum;
99 }
100 lg_H_i += lg_H;
101 }
102 }
103
104 public:
105 CompressedReadStream(u_char* buffer, int position = 0)
106 : CompressedStream(buffer, position) {}
107
108 jboolean read_bool() { return (jboolean) read(); }
109 jbyte read_byte() { return (jbyte ) read(); }
110 jchar read_char() { return (jchar ) read_int(); }
111 jshort read_short() { return (jshort ) read_signed_int(); }
112 jint read_int() { jint b0 = read();
113 if (b0 < L) return b0;
114 else return read_int_mb(b0);
115 }
116 jint read_signed_int();
117 jfloat read_float(); // jfloat_cast(reverse_int(read_int()))
118 jdouble read_double(); // jdouble_cast(2*reverse_int(read_int))
119 jlong read_long(); // jlong_from(2*read_signed_int())
120};
121
122
123class CompressedWriteStream : public CompressedStream {
124 private:
125 bool full() {
126 return _position >= _size;
127 }
128 void store(u_char b) {
129 _buffer[_position++] = b;
130 }
131 void write(u_char b) {
132 if (full()) grow();
133 store(b);
134 }
135 void grow();
136
137 // UNSIGNED5 coding, 1-5 byte cases
138 void write_int_mb(jint value) {
139 juint sum = value;
140 for (int i = 0; ; ) {
141 if (sum < L || i == MAX_i) {
142 // remainder is either a "low code" or the 5th byte
143 assert(sum == (u_char)sum, "valid byte");
144 write((u_char)sum);
145 break;
146 }
147 sum -= L;
148 int b_i = L + (sum % H); // this is a "high code"
149 sum >>= lg_H; // extracted 6 bits
150 write(b_i); ++i;
151 }
152 }
153
154 protected:
155 int _size;
156
157 public:
158 CompressedWriteStream(int initial_size);
159 CompressedWriteStream(u_char* buffer, int initial_size, int position = 0)
160 : CompressedStream(buffer, position) { _size = initial_size; }
161
162 void write_bool(jboolean value) { write(value); }
163 void write_byte(jbyte value) { write(value); }
164 void write_char(jchar value) { write_int(value); }
165 void write_short(jshort value) { write_signed_int(value); }
166 void write_int(jint value) { if ((juint)value < L && !full())
167 store((u_char)value);
168 else write_int_mb(value); }
169 void write_signed_int(jint value) { write_int(encode_sign(value)); }
170 void write_float(jfloat value); // write_int(reverse_int(jint_cast(v)))
171 void write_double(jdouble value); // write_int(reverse_int(<low,high>))
172 void write_long(jlong value); // write_signed_int(<low,high>)
173};
174
175#endif // SHARE_CODE_COMPRESSEDSTREAM_HPP
176