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/* |
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* memsrc.c |
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* |
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* Copyright (C) 1994-1996, Thomas G. Lane. |
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* This file is part of the Independent JPEG Group's software. |
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* For conditions of distribution and use, see the accompanying README file. |
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* |
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* This file contains decompression data source routines for the case of |
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* reading JPEG data from a memory buffer that is preloaded with the entire |
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* JPEG file. This would not seem especially useful at first sight, but |
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* a number of people have asked for it. |
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* This is really just a stripped-down version of jdatasrc.c. Comparison |
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* of this code with jdatasrc.c may be helpful in seeing how to make |
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* custom source managers for other purposes. |
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*/ |
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|
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/* this is not a core library module, so it doesn't define JPEG_INTERNALS */ |
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#include <stdio.h> |
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#include <jpeglib.h> |
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#include <jerror.h> |
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/* Expanded data source object for memory input */ |
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typedef struct { |
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struct jpeg_source_mgr pub; /* public fields */ |
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JOCTET eoi_buffer[2]; /* a place to put a dummy EOI */ |
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} my_source_mgr; |
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typedef my_source_mgr * my_src_ptr; |
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/* |
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* Initialize source --- called by jpeg_read_header |
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* before any data is actually read. |
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*/ |
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METHODDEF(void) |
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init_source (j_decompress_ptr cinfo) |
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{ |
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/* No work, since jpeg_memory_src set up the buffer pointer and count. |
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* Indeed, if we want to read multiple JPEG images from one buffer, |
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* this *must* not do anything to the pointer. |
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*/ |
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} |
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|
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/* |
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* Fill the input buffer --- called whenever buffer is emptied. |
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* |
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* In this application, this routine should never be called; if it is called, |
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* the decompressor has overrun the end of the input buffer, implying we |
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* supplied an incomplete or corrupt JPEG datastream. A simple error exit |
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* might be the most appropriate response. |
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* |
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* But what we choose to do in this code is to supply dummy EOI markers |
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* in order to force the decompressor to finish processing and supply |
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* some sort of output image, no matter how corrupted. |
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*/ |
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|
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METHODDEF(boolean) |
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fill_input_buffer (j_decompress_ptr cinfo) |
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{ |
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my_src_ptr src = (my_src_ptr) cinfo->src; |
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|
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WARNMS(cinfo, JWRN_JPEG_EOF); |
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/* Create a fake EOI marker */ |
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src->eoi_buffer[0] = (JOCTET) 0xFF; |
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src->eoi_buffer[1] = (JOCTET) JPEG_EOI; |
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src->pub.next_input_byte = src->eoi_buffer; |
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src->pub.bytes_in_buffer = 2; |
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return TRUE; |
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} |
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|
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/* |
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* Skip data --- used to skip over a potentially large amount of |
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* uninteresting data (such as an APPn marker). |
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* |
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* If we overrun the end of the buffer, we let fill_input_buffer deal with |
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* it. An extremely large skip could cause some time-wasting here, but |
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* it really isn't supposed to happen ... and the decompressor will never |
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* skip more than 64K anyway. |
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*/ |
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|
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METHODDEF(void) |
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skip_input_data (j_decompress_ptr cinfo, long num_bytes) |
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{ |
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my_src_ptr src = (my_src_ptr) cinfo->src; |
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|
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if (num_bytes > 0) { |
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while (num_bytes > (long) src->pub.bytes_in_buffer) { |
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num_bytes -= (long) src->pub.bytes_in_buffer; |
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(void) fill_input_buffer(cinfo); |
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/* note we assume that fill_input_buffer will never return FALSE, |
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* so suspension need not be handled. |
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*/ |
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} |
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src->pub.next_input_byte += (size_t) num_bytes; |
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src->pub.bytes_in_buffer -= (size_t) num_bytes; |
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} |
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} |
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|
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/* |
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* An additional method that can be provided by data source modules is the |
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* resync_to_restart method for error recovery in the presence of RST markers. |
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* For the moment, this source module just uses the default resync method |
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* provided by the JPEG library. That method assumes that no backtracking |
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* is possible. |
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*/ |
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|
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/* |
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* Terminate source --- called by jpeg_finish_decompress |
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* after all data has been read. Often a no-op. |
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* |
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* NB: *not* called by jpeg_abort or jpeg_destroy; surrounding |
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* application must deal with any cleanup that should happen even |
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* for error exit. |
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*/ |
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|
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METHODDEF(void) |
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term_source (j_decompress_ptr cinfo) |
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{ |
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/* no work necessary here */ |
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} |
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|
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|
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/* |
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* Prepare for input from a memory buffer. |
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*/ |
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|
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GLOBAL(void) |
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jpeg_memory_src (j_decompress_ptr cinfo, const JOCTET * buffer, size_t bufsize) |
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{ |
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my_src_ptr src; |
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|
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/* The source object is made permanent so that a series of JPEG images |
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* can be read from a single buffer by calling jpeg_memory_src |
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* only before the first one. |
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* This makes it unsafe to use this manager and a different source |
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* manager serially with the same JPEG object. Caveat programmer. |
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*/ |
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if (cinfo->src == NULL) { /* first time for this JPEG object? */ |
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cinfo->src = (struct jpeg_source_mgr *) |
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT, |
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sizeof(my_source_mgr)); |
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} |
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src = (my_src_ptr) cinfo->src; |
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src->pub.init_source = init_source; |
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src->pub.fill_input_buffer = fill_input_buffer; |
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src->pub.skip_input_data = skip_input_data; |
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src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */ |
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src->pub.term_source = term_source; |
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src->pub.next_input_byte = buffer; |
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src->pub.bytes_in_buffer = bufsize; |
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} |