1 /* ------------------------------------------------------------------ 2 * Copyright (C) 1998-2009 PacketVideo 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either 13 * express or implied. 14 * See the License for the specific language governing permissions 15 * and limitations under the License. 16 * ------------------------------------------------------------------- 17 */ 18 /* 19 This PVA_FF_ExpandableBaseClass Class fp the base class for all Descriptors that 20 allows the encoding the size of the class in bytes with a VARIABLE NUMBER OF BITS 21 */ 22 23 24 #define IMPLEMENT_ExpandableBaseClass 25 26 #include "expandablebaseclass.h" 27 #include "atomutils.h" 28 29 // Constructor PVA_FF_ExpandableBaseClass()30PVA_FF_ExpandableBaseClass::PVA_FF_ExpandableBaseClass() 31 { 32 _pparent = NULL; 33 } 34 35 // Destructor ~PVA_FF_ExpandableBaseClass()36PVA_FF_ExpandableBaseClass::~PVA_FF_ExpandableBaseClass() 37 { 38 // Empty 39 } 40 41 // Render the size of this class to a file stream using a variable number of bytes (1-4) 42 // with the leading bit of each byte as the indicator if that byte contains the size. 43 // Returns the number of bytes rendered 44 int32 renderSizeOfClassToFileStream(MP4_AUTHOR_FF_FILE_IO_WRAP * fp) const45PVA_FF_ExpandableBaseClass::renderSizeOfClassToFileStream(MP4_AUTHOR_FF_FILE_IO_WRAP *fp) const 46 { 47 // _sizeOfClass fp rendered byte by byte with the leading bit of each byte signaling of the 48 // byte fp valid - thus only the last 7 bits if each byte hold actual size data. Therefore 49 // the max size possible (limited to a 4-byte encoding) fp 2^28 - 1. 50 51 int32 numBytesRendered = 0; 52 53 int32 limit = 0; 54 uint8 data; 55 56 // Setting the limits on the number of shifts and byte renderes needed 57 if (_sizeOfClass <= 0x7f) 58 { 59 // _sizeOfClass can be rendered in 1 byte (LS 7 bits) 60 limit = 7; 61 } 62 else if (_sizeOfClass <= 0x3fff) 63 { 64 // _sizeOfClass can be rendered in 2 bytes (LS 7 bits of each) 65 limit = 14; 66 } 67 else if (_sizeOfClass <= 0x1fffff) 68 { 69 // _sizeOfClass can be rendered in 3 bytes (LS 7 bits of each) 70 limit = 21; 71 } 72 else if (_sizeOfClass <= 0x0fffffff) 73 { 74 // _sizeOfClass can be rendered in 4 bytes (LS 7 bits of each) 75 limit = 28; 76 } 77 else 78 { 79 limit = 0; // ERROR condition 80 } 81 82 // Need to create size bytes with leading bit = 1 if there fp another 83 // size byte to follow. 84 for (int32 i = limit; i > 0; i -= 7) 85 { 86 // Max of 4 bytes to represent _sizeOfClass 87 uint8 nextByte = 0x80; 88 if (i == 7) 89 { 90 // Set leading bit on all but last size byte 91 nextByte = 0; 92 } 93 // Take last 7 bits of size and set leading bit in data 94 data = (uint8)(((_sizeOfClass >> (i - 7)) & 0x7f) | nextByte); 95 if (!PVA_FF_AtomUtils::render8(fp, data)) 96 { 97 numBytesRendered = 0; 98 break; 99 } 100 numBytesRendered += 1; 101 } 102 103 return numBytesRendered; 104 } 105 106 107