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