/*+
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 * jdatasrc.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 file (or any stdio stream).  While these routines+
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 * are sufficient for most applications, some will want to use a different+
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 * source manager.+
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 * IMPORTANT: we assume that fread() will correctly transcribe an array of+
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 * JOCTETs from 8-bit-wide elements on external storage.  If char is wider+
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 * than 8 bits on your machine, you may need to do some tweaking.+
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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 "jinclude.h"+
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#include "jpeglib.h"+
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#include "jerror.h"+
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+
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+
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/* Expanded data source object for stdio input */+
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+
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typedef struct {+
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  struct jpeg_source_mgr pub;	/* public fields */+
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+
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  FILE * infile;		/* source stream */+
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  JOCTET * buffer;		/* start of buffer */+
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  boolean start_of_file;	/* have we gotten any data yet? */+
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} my_source_mgr;+
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+
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typedef my_source_mgr * my_src_ptr;+
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+
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#define INPUT_BUF_SIZE  4096	/* choose an efficiently fread'able size */+
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+
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+
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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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+
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METHODDEF(void)+
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init_source (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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  /* We reset the empty-input-file flag for each image,+
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   * but we don't clear the input buffer.+
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   * This is correct behavior for reading a series of images from one source.+
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   */+
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  src->start_of_file = TRUE;+
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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 typical applications, this should read fresh data into the buffer+
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 * (ignoring the current state of next_input_byte & bytes_in_buffer),+
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 * reset the pointer & count to the start of the buffer, and return TRUE+
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 * indicating that the buffer has been reloaded.  It is not necessary to+
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 * fill the buffer entirely, only to obtain at least one more byte.+
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 *+
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 * There is no such thing as an EOF return.  If the end of the file has been+
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 * reached, the routine has a choice of ERREXIT() or inserting fake data into+
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 * the buffer.  In most cases, generating a warning message and inserting a+
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 * fake EOI marker is the best course of action --- this will allow the+
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 * decompressor to output however much of the image is there.  However,+
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 * the resulting error message is misleading if the real problem is an empty+
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 * input file, so we handle that case specially.+
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 *+
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 * In applications that need to be able to suspend compression due to input+
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 * not being available yet, a FALSE return indicates that no more data can be+
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 * obtained right now, but more may be forthcoming later.  In this situation,+
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 * the decompressor will return to its caller (with an indication of the+
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 * number of scanlines it has read, if any).  The application should resume+
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 * decompression after it has loaded more data into the input buffer.  Note+
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 * that there are substantial restrictions on the use of suspension --- see+
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 * the documentation.+
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 *+
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 * When suspending, the decompressor will back up to a convenient restart point+
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 * (typically the start of the current MCU). next_input_byte & bytes_in_buffer+
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 * indicate where the restart point will be if the current call returns FALSE.+
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 * Data beyond this point must be rescanned after resumption, so move it to+
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 * the front of the buffer rather than discarding it.+
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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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  size_t nbytes;+
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+
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  nbytes = JFREAD(src->infile, src->buffer, INPUT_BUF_SIZE);+
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+
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  if (nbytes <= 0) {+
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    if (src->start_of_file)	/* Treat empty input file as fatal error */+
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      ERREXIT(cinfo, JERR_INPUT_EMPTY);+
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    WARNMS(cinfo, JWRN_JPEG_EOF);+
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    /* Insert a fake EOI marker */+
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    src->buffer[0] = (JOCTET) 0xFF;+
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    src->buffer[1] = (JOCTET) JPEG_EOI;+
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    nbytes = 2;+
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  }+
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+
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  src->pub.next_input_byte = src->buffer;+
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  src->pub.bytes_in_buffer = nbytes;+
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  src->start_of_file = FALSE;+
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+
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  return TRUE;+
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}+
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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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 * Writers of suspendable-input applications must note that skip_input_data+
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 * is not granted the right to give a suspension return.  If the skip extends+
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 * beyond the data currently in the buffer, the buffer can be marked empty so+
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 * that the next read will cause a fill_input_buffer call that can suspend.+
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 * Arranging for additional bytes to be discarded before reloading the input+
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 * buffer is the application writer's problem.+
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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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  /* Just a dumb implementation for now.  Could use fseek() except+
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   * it doesn't work on pipes.  Not clear that being smart is worth+
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   * any trouble anyway --- large skips are infrequent.+
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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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/*+
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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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/*+
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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 stdio stream.+
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 * The caller must have already opened the stream, and is responsible+
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 * for closing it after finishing decompression.+
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 */+
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+
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GLOBAL(void)+
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jpeg_stdio_src (j_decompress_ptr cinfo, FILE * infile)+
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{+
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  my_src_ptr src;+
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+
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  /* The source object and input buffer are made permanent so that a series+
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   * of JPEG images can be read from the same file by calling jpeg_stdio_src+
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   * only before the first one.  (If we discarded the buffer at the end of+
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   * one image, we'd likely lose the start of the next 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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    src = (my_src_ptr) cinfo->src;+
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    src->buffer = (JOCTET *)+
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      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,+
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				  INPUT_BUF_SIZE * SIZEOF(JOCTET));+
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  }+
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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->infile = infile;+
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  src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */+
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  src->pub.next_input_byte = NULL; /* until buffer loaded */+
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}+
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