105 lines
3.4 KiB
C++
105 lines
3.4 KiB
C++
/*
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* Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*
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*/
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#include "precompiled.hpp"
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#include "code/compressedStream.hpp"
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#include "utilities/ostream.hpp"
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// 32-bit self-inverse encoding of float bits
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// converts trailing zeroes (common in floats) to leading zeroes
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inline juint CompressedStream::reverse_int(juint i) {
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// Hacker's Delight, Figure 7-1
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i = (i & 0x55555555) << 1 | ((i >> 1) & 0x55555555);
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i = (i & 0x33333333) << 2 | ((i >> 2) & 0x33333333);
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i = (i & 0x0f0f0f0f) << 4 | ((i >> 4) & 0x0f0f0f0f);
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i = (i << 24) | ((i & 0xff00) << 8) | ((i >> 8) & 0xff00) | (i >> 24);
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return i;
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}
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jint CompressedReadStream::read_signed_int() {
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return decode_sign(read_int());
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}
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// Compressing floats is simple, because the only common pattern
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// is trailing zeroes. (Compare leading sign bits on ints.)
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// Since floats are left-justified, as opposed to right-justified
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// ints, we can bit-reverse them in order to take advantage of int
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// compression.
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jfloat CompressedReadStream::read_float() {
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int rf = read_int();
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int f = reverse_int(rf);
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return jfloat_cast(f);
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}
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jdouble CompressedReadStream::read_double() {
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jint rh = read_int();
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jint rl = read_int();
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jint h = reverse_int(rh);
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jint l = reverse_int(rl);
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return jdouble_cast(jlong_from(h, l));
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}
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jlong CompressedReadStream::read_long() {
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jint low = read_signed_int();
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jint high = read_signed_int();
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return jlong_from(high, low);
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}
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CompressedWriteStream::CompressedWriteStream(int initial_size) : CompressedStream(NULL, 0) {
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_buffer = NEW_RESOURCE_ARRAY(u_char, initial_size);
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_size = initial_size;
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_position = 0;
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}
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void CompressedWriteStream::grow() {
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u_char* _new_buffer = NEW_RESOURCE_ARRAY(u_char, _size * 2);
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memcpy(_new_buffer, _buffer, _position);
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_buffer = _new_buffer;
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_size = _size * 2;
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}
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void CompressedWriteStream::write_float(jfloat value) {
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juint f = jint_cast(value);
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juint rf = reverse_int(f);
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assert(f == reverse_int(rf), "can re-read same bits");
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write_int(rf);
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}
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void CompressedWriteStream::write_double(jdouble value) {
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juint h = high(jlong_cast(value));
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juint l = low( jlong_cast(value));
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juint rh = reverse_int(h);
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juint rl = reverse_int(l);
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assert(h == reverse_int(rh), "can re-read same bits");
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assert(l == reverse_int(rl), "can re-read same bits");
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write_int(rh);
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write_int(rl);
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}
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void CompressedWriteStream::write_long(jlong value) {
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write_signed_int(low(value));
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write_signed_int(high(value));
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}
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