4 * This file was part of the Independent JPEG Group's software:
5 * Copyright (C) 1991-1997, Thomas G. Lane.
6 * libjpeg-turbo Modifications:
7 * Copyright (C) 2022, D. R. Commander.
8 * For conditions of distribution and use, see the accompanying README.ijg
11 * This file contains declarations for Huffman entropy encoding routines
12 * that are shared between the sequential encoder (jchuff.c) and the
13 * progressive encoder (jcphuff.c). No other modules need to see these.
16 /* The legal range of a DCT coefficient is
17 * -1024 .. +1023 for 8-bit data;
18 * -16384 .. +16383 for 12-bit data.
19 * Hence the magnitude should always fit in 10 or 14 bits respectively.
22 /* The progressive Huffman encoder uses an unsigned 16-bit data type to store
23 * absolute values of coefficients, because it is possible to inject a
24 * coefficient value of -32768 into the encoder by attempting to transform a
25 * malformed 12-bit JPEG image, and the absolute value of -32768 would overflow
26 * a signed 16-bit integer.
28 typedef unsigned short UJCOEF;
30 /* Derived data constructed for each Huffman table */
33 unsigned int ehufco[256]; /* code for each symbol */
34 char ehufsi[256]; /* length of code for each symbol */
35 /* If no code has been allocated for a symbol S, ehufsi[S] contains 0 */
38 /* Expand a Huffman table definition into the derived format */
39 EXTERN(void) jpeg_make_c_derived_tbl(j_compress_ptr cinfo, boolean isDC,
40 int tblno, c_derived_tbl **pdtbl);
42 /* Generate an optimal table definition given the specified counts */
43 EXTERN(void) jpeg_gen_optimal_table(j_compress_ptr cinfo, JHUFF_TBL *htbl,