1 /*
2 * Copyright (c) 1997, 2010, 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.
22 *
23 */
24
25 #ifndef SHARE_VM_CODE_COMPRESSEDSTREAM_HPP
26 #define SHARE_VM_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
33 class 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 // these inlines are defined only in compressedStream.cpp
47 static inline juint encode_sign(jint value); // for Pack200 SIGNED5
48 static inline jint decode_sign(juint value); // for Pack200 SIGNED5
49 static inline juint reverse_int(juint bits); // to trim trailing float 0's
50
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
65 class 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
123 class 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 void write_int_mb(jint value); // UNSIGNED5 coding, 1-5 byte cases
138
139 protected:
140 int _size;
141
142 public:
143 CompressedWriteStream(int initial_size);
144 CompressedWriteStream(u_char* buffer, int initial_size, int position = 0)
145 : CompressedStream(buffer, position) { _size = initial_size; }
146
147 void write_bool(jboolean value) { write(value); }
148 void write_byte(jbyte value) { write(value); }
149 void write_char(jchar value) { write_int(value); }
150 void write_short(jshort value) { write_signed_int(value); }
151 void write_int(jint value) { if ((juint)value < L && !full())
152 store((u_char)value);
153 else write_int_mb(value); }
154 void write_signed_int(jint value); // write_int(encode_sign(value))
155 void write_float(jfloat value); // write_int(reverse_int(jint_cast(v)))
156 void write_double(jdouble value); // write_int(reverse_int(<low,high>))
157 void write_long(jlong value); // write_signed_int(<low,high>)
158 };
159
160 #endif // SHARE_VM_CODE_COMPRESSEDSTREAM_HPP