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| 1 /* |
| 2 * Copyright 2013 Google Inc. |
| 3 * |
| 4 * Use of this source code is governed by a BSD-style license that can be |
| 5 * found in the LICENSE file. |
| 6 */ |
| 7 |
| 8 #include "SkFrontBufferedStream.h" |
| 9 |
| 10 SkFrontBufferedStream* SkFrontBufferedStream::Create(SkStream* stream, size_t bu
fferSize) { |
| 11 if (NULL == stream) { |
| 12 return NULL; |
| 13 } |
| 14 return SkNEW_ARGS(SkFrontBufferedStream, (stream, bufferSize)); |
| 15 } |
| 16 |
| 17 SkFrontBufferedStream::SkFrontBufferedStream(SkStream* stream, size_t bufferSize
) |
| 18 : fStream(SkRef(stream)) |
| 19 , fOffset(0) |
| 20 , fBufferedSoFar(0) |
| 21 , fBufferSize(bufferSize) |
| 22 , fBuffer(bufferSize) {} |
| 23 |
| 24 bool SkFrontBufferedStream::isAtEnd() const { |
| 25 if (fOffset < fBufferedSoFar) { |
| 26 // Even if the underlying stream is at the end, this stream has been |
| 27 // rewound after buffering, so it is not at the end. |
| 28 return false; |
| 29 } |
| 30 |
| 31 return fStream->isAtEnd(); |
| 32 } |
| 33 |
| 34 bool SkFrontBufferedStream::rewind() { |
| 35 // Only allow a rewind if we have not exceeded the buffer. |
| 36 if (fOffset <= fBufferSize) { |
| 37 fOffset = 0; |
| 38 return true; |
| 39 } |
| 40 return false; |
| 41 } |
| 42 |
| 43 bool SkFrontBufferedStream::hasLength() const { |
| 44 return fStream->hasLength(); |
| 45 } |
| 46 |
| 47 size_t SkFrontBufferedStream::getLength() const { |
| 48 return fStream->getLength(); |
| 49 } |
| 50 |
| 51 size_t SkFrontBufferedStream::read(void* voidDst, size_t size) { |
| 52 // Cast voidDst to a char* for easy addition. |
| 53 char* dst = reinterpret_cast<char*>(voidDst); |
| 54 SkDEBUGCODE(const size_t totalSize = size;) |
| 55 size_t readSoFar = 0; |
| 56 |
| 57 // First, read any data that was previously buffered. |
| 58 if (fOffset < fBufferedSoFar) { |
| 59 // Some data has already been copied to fBuffer. Read up to the |
| 60 // lesser of the size requested and the remainder of the buffered |
| 61 // data. |
| 62 const size_t bytesToCopy = SkTMin(size, fBufferedSoFar - fOffset); |
| 63 if (dst != NULL) { |
| 64 memcpy(dst, this->getBufferAtOffset(), bytesToCopy); |
| 65 } |
| 66 |
| 67 // Update fOffset to the new position. It is guaranteed to be |
| 68 // within the buffered data. |
| 69 fOffset += bytesToCopy; |
| 70 SkASSERT(fOffset <= fBufferedSoFar); |
| 71 |
| 72 if (bytesToCopy == size) { |
| 73 // The entire requested read was inside the already buffered |
| 74 // data. |
| 75 SkASSERT(fOffset <= fBufferedSoFar); |
| 76 return size; |
| 77 } |
| 78 |
| 79 // The requested read extends beyond the buffered data. Update |
| 80 // the remaining number of bytes needed to read, the number of |
| 81 // bytes read so far, and the destination buffer. |
| 82 size -= bytesToCopy; |
| 83 readSoFar += bytesToCopy; |
| 84 SkASSERT(size + readSoFar == totalSize); |
| 85 if (dst != NULL) { |
| 86 dst += bytesToCopy; |
| 87 } |
| 88 } |
| 89 |
| 90 // If we got here, we have read everything that was already buffered. |
| 91 SkASSERT(fOffset >= fBufferedSoFar); |
| 92 |
| 93 // Buffer any more data that should be buffered, and copy it to the |
| 94 // destination. |
| 95 if (fBufferedSoFar < fBufferSize) { |
| 96 // Data needs to be buffered. Buffer up to the lesser of the size reques
ted |
| 97 // and the remainder of the max buffer size. |
| 98 const size_t bytesToBuffer = SkTMin(size, fBufferSize - fBufferedSoFar); |
| 99 char* buffer = this->getBufferAtOffset(); |
| 100 const size_t buffered = fStream->read(buffer, bytesToBuffer); |
| 101 fBufferedSoFar += buffered; |
| 102 fOffset = fBufferedSoFar; |
| 103 |
| 104 // Copy the buffer to the destination buffer and update the amount read. |
| 105 if (dst != NULL) { |
| 106 memcpy(dst, buffer, buffered); |
| 107 } |
| 108 readSoFar += buffered; |
| 109 |
| 110 if (buffered == size || fStream->isAtEnd()) { |
| 111 // We were able to buffer all of the data requested (or all the data |
| 112 // remaining in the stream) and provide it to the caller. |
| 113 SkASSERT(fBufferedSoFar <= fBufferSize); |
| 114 SkASSERT(totalSize == readSoFar || fStream->isAtEnd()); |
| 115 return readSoFar; |
| 116 } |
| 117 |
| 118 // The requested read extends beyond the length of the buffer. Update |
| 119 // the remaining number of bytes needed to read and the destination |
| 120 // buffer. |
| 121 size -= buffered; |
| 122 SkASSERT(size + readSoFar == totalSize); |
| 123 if (dst != NULL) { |
| 124 dst += buffered; |
| 125 } |
| 126 } |
| 127 |
| 128 // If we get here, we have buffered all that can be buffered. |
| 129 SkASSERT(fBufferSize == fBufferedSoFar && fOffset >= fBufferSize); |
| 130 |
| 131 // Read directly from the stream. |
| 132 const size_t bytesReadDirectly = fStream->read(dst, size); |
| 133 fOffset += bytesReadDirectly; |
| 134 return bytesReadDirectly + readSoFar; |
| 135 } |
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