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* 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.
#define MAX_COEF_BITS 10
#define MAX_COEF_BITS 14
/* 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[]);