kc3-lang/libjpeg-turbo/src/jchuff.h

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• Hash : e69dd40c
  Author :
  Date : 2024-01-23T13:26:41
  

  Reorganize source to make things easier to find
  
  - Move all libjpeg documentation, except for README.ijg, into the doc/
    subdirectory.
  
  - Move the TurboJPEG C API documentation from doc/html/ into
    doc/turbojpeg/.
  
  - Move all C source code and headers into a src/ subdirectory.
  
  - Move turbojpeg-jni.c into the java/ subdirectory.
  
  Referring to #226, there is no ideal solution to this problem.  A
  semantically ideal solution would have involved placing all source code,
  including the SIMD and Java source code, under src/ (or perhaps placing
  C library source code under lib/ and C test program source code under
  test/), all header files under include/, and all documentation under
  doc/.  However:
  
  - To me it makes more sense to have separate top-level directories for
    each language, since the SIMD extensions and the Java API are
    technically optional features.  src/ now contains only the code that
    is relevant to the core C API libraries and associated programs.
  - I didn't want to bury the java/ and simd/ directories or add a level
    of depth to them, since both directories already contain source code
    that is 3-4 levels deep.
  - I would prefer not to separate the header files from the C source
    code, because:
    1. It would be disruptive.  libjpeg and libjpeg-turbo have
       historically placed C source code and headers in the same
       directory, and people who are familiar with both projects (self
       included) are used to looking for the headers in the same directory
       as the C source code.
    2. In terms of how the headers are used internally in libjpeg-turbo,
       the distinction between public and private headers is a bit fuzzy.
  - It didn't make sense to separate the test source code from the library
    source code, since there is not a clear distinction in some cases.
    (For instance, the IJG image I/O functions are used by cjpeg and djpeg
    as well as by the TurboJPEG API.)
  
  This solution is minimally disruptive, since it keeps all C source code
  and headers together and keeps java/ and simd/ as top-level directories.
  It is a bit awkward, because java/ and simd/ technically contain source
  code, even though they are not under src/.  However, other solutions
  would have been more awkward for different reasons.
  
  Closes #226
  

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• src/jchuff.h

• /*
   * jchuff.h
   *
   * This file was part of the Independent JPEG Group's software:
   * Copyright (C) 1991-1997, Thomas G. Lane.
   * libjpeg-turbo Modifications:
   * Copyright (C) 2022, D. R. Commander.
   * For conditions of distribution and use, see the accompanying README.ijg
   * file.
   *
   * This file contains declarations for Huffman entropy encoding routines
   * that are shared between the sequential encoder (jchuff.c) and the
   * progressive encoder (jcphuff.c).  No other modules need to see these.
   */
  
  /* The legal range of a DCT coefficient is
   *  -1024 .. +1023  for 8-bit data;
   * -16384 .. +16383 for 12-bit data.
   * Hence the magnitude should always fit in 10 or 14 bits respectively.
   */
  
  /* The progressive Huffman encoder uses an unsigned 16-bit data type to store
   * absolute values of coefficients, because it is possible to inject a
   * coefficient value of -32768 into the encoder by attempting to transform a
   * malformed 12-bit JPEG image, and the absolute value of -32768 would overflow
   * a signed 16-bit integer.
   */
  typedef unsigned short UJCOEF;
  
  /* Derived data constructed for each Huffman table */
  
  typedef struct {
    unsigned int ehufco[256];     /* code for each symbol */
    char ehufsi[256];             /* length of code for each symbol */
    /* If no code has been allocated for a symbol S, ehufsi[S] contains 0 */
  } c_derived_tbl;
  
  /* Expand a Huffman table definition into the derived format */
  EXTERN(void) jpeg_make_c_derived_tbl(j_compress_ptr cinfo, boolean isDC,
                                       int tblno, c_derived_tbl **pdtbl);
  
  /* Generate an optimal table definition given the specified counts */
  EXTERN(void) jpeg_gen_optimal_table(j_compress_ptr cinfo, JHUFF_TBL *htbl,
                                      long freq[]);
  

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