michael@0: /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
michael@0:  * vim: set ts=8 sts=4 et sw=4 tw=99:
michael@0:  * This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #ifndef jit_Compactbuffer_h
michael@0: #define jit_Compactbuffer_h
michael@0: 
michael@0: #include "jsalloc.h"
michael@0: 
michael@0: #include "jit/IonTypes.h"
michael@0: #include "js/Vector.h"
michael@0: 
michael@0: namespace js {
michael@0: namespace jit {
michael@0: 
michael@0: class CompactBufferWriter;
michael@0: 
michael@0: // CompactBuffers are byte streams designed for compressable integers. It has
michael@0: // helper functions for writing bytes, fixed-size integers, and variable-sized
michael@0: // integers. Variable sized integers are encoded in 1-5 bytes, each byte
michael@0: // containing 7 bits of the integer and a bit which specifies whether the next
michael@0: // byte is also part of the integer.
michael@0: //
michael@0: // Fixed-width integers are also available, in case the actual value will not
michael@0: // be known until later.
michael@0: 
michael@0: class CompactBufferReader
michael@0: {
michael@0:     const uint8_t *buffer_;
michael@0:     const uint8_t *end_;
michael@0: 
michael@0:     uint32_t readVariableLength() {
michael@0:         uint32_t val = 0;
michael@0:         uint32_t shift = 0;
michael@0:         uint8_t byte;
michael@0:         while (true) {
michael@0:             JS_ASSERT(shift < 32);
michael@0:             byte = readByte();
michael@0:             val |= (uint32_t(byte) >> 1) << shift;
michael@0:             shift += 7;
michael@0:             if (!(byte & 1))
michael@0:                 return val;
michael@0:         }
michael@0:         MOZ_ASSUME_UNREACHABLE("unreachable");
michael@0:     }
michael@0: 
michael@0:   public:
michael@0:     CompactBufferReader(const uint8_t *start, const uint8_t *end)
michael@0:       : buffer_(start),
michael@0:         end_(end)
michael@0:     { }
michael@0:     inline CompactBufferReader(const CompactBufferWriter &writer);
michael@0:     uint8_t readByte() {
michael@0:         JS_ASSERT(buffer_ < end_);
michael@0:         return *buffer_++;
michael@0:     }
michael@0:     uint32_t readFixedUint32_t() {
michael@0:         uint32_t b0 = readByte();
michael@0:         uint32_t b1 = readByte();
michael@0:         uint32_t b2 = readByte();
michael@0:         uint32_t b3 = readByte();
michael@0:         return b0 | (b1 << 8) | (b2 << 16) | (b3 << 24);
michael@0:     }
michael@0:     uint16_t readFixedUint16_t() {
michael@0:         uint32_t b0 = readByte();
michael@0:         uint32_t b1 = readByte();
michael@0:         return b0 | (b1 << 8);
michael@0:     }
michael@0:     uint32_t readUnsigned() {
michael@0:         return readVariableLength();
michael@0:     }
michael@0:     int32_t readSigned() {
michael@0:         uint8_t b = readByte();
michael@0:         bool isNegative = !!(b & (1 << 0));
michael@0:         bool more = !!(b & (1 << 1));
michael@0:         int32_t result = b >> 2;
michael@0:         if (more)
michael@0:             result |= readUnsigned() << 6;
michael@0:         if (isNegative)
michael@0:             return -result;
michael@0:         return result;
michael@0:     }
michael@0: 
michael@0:     bool more() const {
michael@0:         JS_ASSERT(buffer_ <= end_);
michael@0:         return buffer_ < end_;
michael@0:     }
michael@0: 
michael@0:     void seek(const uint8_t *start, uint32_t offset) {
michael@0:         buffer_ = start + offset;
michael@0:         MOZ_ASSERT(start < end_);
michael@0:         MOZ_ASSERT(buffer_ < end_);
michael@0:     }
michael@0: };
michael@0: 
michael@0: class CompactBufferWriter
michael@0: {
michael@0:     js::Vector<uint8_t, 32, SystemAllocPolicy> buffer_;
michael@0:     bool enoughMemory_;
michael@0: 
michael@0:   public:
michael@0:     CompactBufferWriter()
michael@0:       : enoughMemory_(true)
michael@0:     { }
michael@0: 
michael@0:     // Note: writeByte() takes uint32 to catch implicit casts with a runtime
michael@0:     // assert.
michael@0:     void writeByte(uint32_t byte) {
michael@0:         JS_ASSERT(byte <= 0xFF);
michael@0:         enoughMemory_ &= buffer_.append(byte);
michael@0:     }
michael@0:     void writeUnsigned(uint32_t value) {
michael@0:         do {
michael@0:             uint8_t byte = ((value & 0x7F) << 1) | (value > 0x7F);
michael@0:             writeByte(byte);
michael@0:             value >>= 7;
michael@0:         } while (value);
michael@0:     }
michael@0:     void writeSigned(int32_t v) {
michael@0:         bool isNegative = v < 0;
michael@0:         uint32_t value = isNegative ? -v : v;
michael@0:         uint8_t byte = ((value & 0x3F) << 2) | ((value > 0x3F) << 1) | uint32_t(isNegative);
michael@0:         writeByte(byte);
michael@0: 
michael@0:         // Write out the rest of the bytes, if needed.
michael@0:         value >>= 6;
michael@0:         if (value == 0)
michael@0:             return;
michael@0:         writeUnsigned(value);
michael@0:     }
michael@0:     void writeFixedUint32_t(uint32_t value) {
michael@0:         writeByte(value & 0xFF);
michael@0:         writeByte((value >> 8) & 0xFF);
michael@0:         writeByte((value >> 16) & 0xFF);
michael@0:         writeByte((value >> 24) & 0xFF);
michael@0:     }
michael@0:     void writeFixedUint16_t(uint16_t value) {
michael@0:         writeByte(value & 0xFF);
michael@0:         writeByte(value >> 8);
michael@0:     }
michael@0:     size_t length() const {
michael@0:         return buffer_.length();
michael@0:     }
michael@0:     uint8_t *buffer() {
michael@0:         return &buffer_[0];
michael@0:     }
michael@0:     const uint8_t *buffer() const {
michael@0:         return &buffer_[0];
michael@0:     }
michael@0:     bool oom() const {
michael@0:         return !enoughMemory_;
michael@0:     }
michael@0: };
michael@0: 
michael@0: CompactBufferReader::CompactBufferReader(const CompactBufferWriter &writer)
michael@0:   : buffer_(writer.buffer()),
michael@0:     end_(writer.buffer() + writer.length())
michael@0: {
michael@0: }
michael@0: 
michael@0: } // namespace jit
michael@0: } // namespace js
michael@0: 
michael@0: #endif /* jit_Compactbuffer_h */