kc3-lang/libjpeg-turbo/jdatasrc.c

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• Hash : e8b40f3c
  Author :
  Date : 2022-11-01T21:45:39
  

  Vastly improve 12-bit JPEG integration
  
  The Gordian knot that 7fec5074f962b20ed00b4f5da4533e1e8d4ed8ac attempted
  to unravel was caused by the fact that there are several
  data-precision-dependent (JSAMPLE-dependent) fields and methods in the
  exposed libjpeg API structures, and if you change the exposed libjpeg
  API structures, then you have to change the whole API.  If you change
  the whole API, then you have to provide a whole new library to support
  the new API, and that makes it difficult to support multiple data
  precisions in the same application.  (It is not impossible, as example.c
  demonstrated, but using data-precision-dependent libjpeg API structures
  would have made the cjpeg, djpeg, and jpegtran source code hard to read,
  so it made more sense to build, install, and package 12-bit-specific
  versions of those applications.)
  
  Unfortunately, the result of that initial integration effort was an
  unreadable and unmaintainable mess, which is a problem for a library
  that is an ISO/ITU-T reference implementation.  Also, as I dug into the
  problem of lossless JPEG support, I realized that 16-bit lossless JPEG
  images are a thing, and supporting yet another version of the libjpeg
  API just for those images is untenable.
  
  In fact, however, the touch points for JSAMPLE in the exposed libjpeg
  API structures are minimal:
  
    - The colormap and sample_range_limit fields in jpeg_decompress_struct
    - The alloc_sarray() and access_virt_sarray() methods in
      jpeg_memory_mgr
    - jpeg_write_scanlines() and jpeg_write_raw_data()
    - jpeg_read_scanlines() and jpeg_read_raw_data()
    - jpeg_skip_scanlines() and jpeg_crop_scanline()
      (This is subtle, but both of those functions use JSAMPLE-dependent
      opaque structures behind the scenes.)
  
  It is much more readable and maintainable to provide 12-bit-specific
  versions of those six top-level API functions and to document that the
  aforementioned methods and fields must be type-cast when using 12-bit
  samples.  Since that eliminates the need to provide a 12-bit-specific
  version of the exposed libjpeg API structures, we can:
  
    - Compile only the precision-dependent libjpeg modules (the
      coefficient buffer controllers, the colorspace converters, the
      DCT/IDCT managers, the main buffer controllers, the preprocessing
      and postprocessing controller, the downsampler and upsamplers, the
      quantizers, the integer DCT methods, and the IDCT methods) for
      multiple data precisions.
    - Introduce 12-bit-specific methods into the various internal
      structures defined in jpegint.h.
    - Create precision-independent data type, macro, method, field, and
      function names that are prefixed by an underscore, and use an
      internal header to convert those into precision-dependent data
      type, macro, method, field, and function names, based on the value
      of BITS_IN_JSAMPLE, when compiling the precision-dependent libjpeg
      modules.
    - Expose precision-dependent jinit*() functions for each of the
      precision-dependent libjpeg modules.
    - Abstract the precision-dependent libjpeg modules by calling the
      appropriate precision-dependent jinit*() function, based on the
      value of cinfo->data_precision, from top-level libjpeg API
      functions.
  

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• jdatasrc.c

• /*
   * jdatasrc.c
   *
   * This file was part of the Independent JPEG Group's software:
   * Copyright (C) 1994-1996, Thomas G. Lane.
   * Modified 2009-2011 by Guido Vollbeding.
   * libjpeg-turbo Modifications:
   * Copyright (C) 2013, 2016, 2022, D. R. Commander.
   * For conditions of distribution and use, see the accompanying README.ijg
   * file.
   *
   * This file contains decompression data source routines for the case of
   * reading JPEG data from memory or from a file (or any stdio stream).
   * While these routines are sufficient for most applications,
   * some will want to use a different source manager.
   * IMPORTANT: we assume that fread() will correctly transcribe an array of
   * JOCTETs from 8-bit-wide elements on external storage.  If char is wider
   * than 8 bits on your machine, you may need to do some tweaking.
   */
  
  /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
  #include "jinclude.h"
  #include "jpeglib.h"
  #include "jerror.h"
  
  
  /* Expanded data source object for stdio input */
  
  typedef struct {
    struct jpeg_source_mgr pub;   /* public fields */
  
    FILE *infile;                 /* source stream */
    JOCTET *buffer;               /* start of buffer */
    boolean start_of_file;        /* have we gotten any data yet? */
  } my_source_mgr;
  
  typedef my_source_mgr *my_src_ptr;
  
  #define INPUT_BUF_SIZE  4096    /* choose an efficiently fread'able size */
  
  
  /*
   * Initialize source --- called by jpeg_read_header
   * before any data is actually read.
   */
  
  METHODDEF(void)
  init_source(j_decompress_ptr cinfo)
  {
    my_src_ptr src = (my_src_ptr)cinfo->src;
  
    /* We reset the empty-input-file flag for each image,
     * but we don't clear the input buffer.
     * This is correct behavior for reading a series of images from one source.
     */
    src->start_of_file = TRUE;
  }
  
  METHODDEF(void)
  init_mem_source(j_decompress_ptr cinfo)
  {
    /* no work necessary here */
  }
  
  
  /*
   * Fill the input buffer --- called whenever buffer is emptied.
   *
   * In typical applications, this should read fresh data into the buffer
   * (ignoring the current state of next_input_byte & bytes_in_buffer),
   * reset the pointer & count to the start of the buffer, and return TRUE
   * indicating that the buffer has been reloaded.  It is not necessary to
   * fill the buffer entirely, only to obtain at least one more byte.
   *
   * There is no such thing as an EOF return.  If the end of the file has been
   * reached, the routine has a choice of ERREXIT() or inserting fake data into
   * the buffer.  In most cases, generating a warning message and inserting a
   * fake EOI marker is the best course of action --- this will allow the
   * decompressor to output however much of the image is there.  However,
   * the resulting error message is misleading if the real problem is an empty
   * input file, so we handle that case specially.
   *
   * In applications that need to be able to suspend compression due to input
   * not being available yet, a FALSE return indicates that no more data can be
   * obtained right now, but more may be forthcoming later.  In this situation,
   * the decompressor will return to its caller (with an indication of the
   * number of scanlines it has read, if any).  The application should resume
   * decompression after it has loaded more data into the input buffer.  Note
   * that there are substantial restrictions on the use of suspension --- see
   * the documentation.
   *
   * When suspending, the decompressor will back up to a convenient restart point
   * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
   * indicate where the restart point will be if the current call returns FALSE.
   * Data beyond this point must be rescanned after resumption, so move it to
   * the front of the buffer rather than discarding it.
   */
  
  METHODDEF(boolean)
  fill_input_buffer(j_decompress_ptr cinfo)
  {
    my_src_ptr src = (my_src_ptr)cinfo->src;
    size_t nbytes;
  
    nbytes = fread(src->buffer, 1, INPUT_BUF_SIZE, src->infile);
  
    if (nbytes <= 0) {
      if (src->start_of_file)     /* Treat empty input file as fatal error */
        ERREXIT(cinfo, JERR_INPUT_EMPTY);
      WARNMS(cinfo, JWRN_JPEG_EOF);
      /* Insert a fake EOI marker */
      src->buffer[0] = (JOCTET)0xFF;
      src->buffer[1] = (JOCTET)JPEG_EOI;
      nbytes = 2;
    }
  
    src->pub.next_input_byte = src->buffer;
    src->pub.bytes_in_buffer = nbytes;
    src->start_of_file = FALSE;
  
    return TRUE;
  }
  
  METHODDEF(boolean)
  fill_mem_input_buffer(j_decompress_ptr cinfo)
  {
    static const JOCTET mybuffer[4] = {
      (JOCTET)0xFF, (JOCTET)JPEG_EOI, 0, 0
    };
  
    /* The whole JPEG data is expected to reside in the supplied memory
     * buffer, so any request for more data beyond the given buffer size
     * is treated as an error.
     */
    WARNMS(cinfo, JWRN_JPEG_EOF);
  
    /* Insert a fake EOI marker */
  
    cinfo->src->next_input_byte = mybuffer;
    cinfo->src->bytes_in_buffer = 2;
  
    return TRUE;
  }
  
  
  /*
   * Skip data --- used to skip over a potentially large amount of
   * uninteresting data (such as an APPn marker).
   *
   * Writers of suspendable-input applications must note that skip_input_data
   * is not granted the right to give a suspension return.  If the skip extends
   * beyond the data currently in the buffer, the buffer can be marked empty so
   * that the next read will cause a fill_input_buffer call that can suspend.
   * Arranging for additional bytes to be discarded before reloading the input
   * buffer is the application writer's problem.
   */
  
  METHODDEF(void)
  skip_input_data(j_decompress_ptr cinfo, long num_bytes)
  {
    struct jpeg_source_mgr *src = cinfo->src;
  
    /* Just a dumb implementation for now.  Could use fseek() except
     * it doesn't work on pipes.  Not clear that being smart is worth
     * any trouble anyway --- large skips are infrequent.
     */
    if (num_bytes > 0) {
      while (num_bytes > (long)src->bytes_in_buffer) {
        num_bytes -= (long)src->bytes_in_buffer;
        (void)(*src->fill_input_buffer) (cinfo);
        /* note we assume that fill_input_buffer will never return FALSE,
         * so suspension need not be handled.
         */
      }
      src->next_input_byte += (size_t)num_bytes;
      src->bytes_in_buffer -= (size_t)num_bytes;
    }
  }
  
  
  /*
   * An additional method that can be provided by data source modules is the
   * resync_to_restart method for error recovery in the presence of RST markers.
   * For the moment, this source module just uses the default resync method
   * provided by the JPEG library.  That method assumes that no backtracking
   * is possible.
   */
  
  
  /*
   * Terminate source --- called by jpeg_finish_decompress
   * after all data has been read.  Often a no-op.
   *
   * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
   * application must deal with any cleanup that should happen even
   * for error exit.
   */
  
  METHODDEF(void)
  term_source(j_decompress_ptr cinfo)
  {
    /* no work necessary here */
  }
  
  
  /*
   * Prepare for input from a stdio stream.
   * The caller must have already opened the stream, and is responsible
   * for closing it after finishing decompression.
   */
  
  GLOBAL(void)
  jpeg_stdio_src(j_decompress_ptr cinfo, FILE *infile)
  {
    my_src_ptr src;
  
    /* The source object and input buffer are made permanent so that a series
     * of JPEG images can be read from the same file by calling jpeg_stdio_src
     * only before the first one.  (If we discarded the buffer at the end of
     * one image, we'd likely lose the start of the next one.)
     */
    if (cinfo->src == NULL) {     /* first time for this JPEG object? */
      cinfo->src = (struct jpeg_source_mgr *)
        (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_PERMANENT,
                                    sizeof(my_source_mgr));
      src = (my_src_ptr)cinfo->src;
      src->buffer = (JOCTET *)
        (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_PERMANENT,
                                    INPUT_BUF_SIZE * sizeof(JOCTET));
    } else if (cinfo->src->init_source != init_source) {
      /* It is unsafe to reuse the existing source manager unless it was created
       * by this function.  Otherwise, there is no guarantee that the opaque
       * structure is the right size.  Note that we could just create a new
       * structure, but the old structure would not be freed until
       * jpeg_destroy_decompress() was called.
       */
      ERREXIT(cinfo, JERR_BUFFER_SIZE);
    }
  
    src = (my_src_ptr)cinfo->src;
    src->pub.init_source = init_source;
    src->pub.fill_input_buffer = fill_input_buffer;
    src->pub.skip_input_data = skip_input_data;
    src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
    src->pub.term_source = term_source;
    src->infile = infile;
    src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
    src->pub.next_input_byte = NULL; /* until buffer loaded */
  }
  
  
  /*
   * Prepare for input from a supplied memory buffer.
   * The buffer must contain the whole JPEG data.
   */
  
  GLOBAL(void)
  jpeg_mem_src(j_decompress_ptr cinfo, const unsigned char *inbuffer,
               unsigned long insize)
  {
    struct jpeg_source_mgr *src;
  
    if (inbuffer == NULL || insize == 0)  /* Treat empty input as fatal error */
      ERREXIT(cinfo, JERR_INPUT_EMPTY);
  
    /* The source object is made permanent so that a series of JPEG images
     * can be read from the same buffer by calling jpeg_mem_src only before
     * the first one.
     */
    if (cinfo->src == NULL) {     /* first time for this JPEG object? */
      cinfo->src = (struct jpeg_source_mgr *)
        (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_PERMANENT,
                                    sizeof(struct jpeg_source_mgr));
    } else if (cinfo->src->init_source != init_mem_source) {
      /* It is unsafe to reuse the existing source manager unless it was created
       * by this function.
       */
      ERREXIT(cinfo, JERR_BUFFER_SIZE);
    }
  
    src = cinfo->src;
    src->init_source = init_mem_source;
    src->fill_input_buffer = fill_mem_input_buffer;
    src->skip_input_data = skip_input_data;
    src->resync_to_restart = jpeg_resync_to_restart; /* use default method */
    src->term_source = term_source;
    src->bytes_in_buffer = (size_t)insize;
    src->next_input_byte = (const JOCTET *)inbuffer;
  }
  

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