4 * This file was part of the Independent JPEG Group's software:
5 * Copyright (C) 1994-1997, Thomas G. Lane.
6 * libjpeg-turbo Modifications:
7 * Copyright 2009 Pierre Ossman <ossman@cendio.se> for Cendio AB
8 * Copyright (C) 2020, Google, Inc.
9 * Copyright (C) 2022, D. R. Commander.
10 * For conditions of distribution and use, see the accompanying README.ijg
14 #define JPEG_INTERNALS
18 #if BITS_IN_JSAMPLE != 16 || defined(D_LOSSLESS_SUPPORTED)
20 /* Block smoothing is only applicable for progressive JPEG, so: */
21 #ifndef D_PROGRESSIVE_SUPPORTED
22 #undef BLOCK_SMOOTHING_SUPPORTED
26 /* Private buffer controller object */
29 struct jpeg_d_coef_controller pub; /* public fields */
31 /* These variables keep track of the current location of the input side. */
32 /* cinfo->input_iMCU_row is also used for this. */
33 JDIMENSION MCU_ctr; /* counts MCUs processed in current row */
34 int MCU_vert_offset; /* counts MCU rows within iMCU row */
35 int MCU_rows_per_iMCU_row; /* number of such rows needed */
37 /* The output side's location is represented by cinfo->output_iMCU_row. */
39 /* In single-pass modes, it's sufficient to buffer just one MCU.
40 * We allocate a workspace of D_MAX_BLOCKS_IN_MCU coefficient blocks,
41 * and let the entropy decoder write into that workspace each time.
42 * In multi-pass modes, this array points to the current MCU's blocks
43 * within the virtual arrays; it is used only by the input side.
45 JBLOCKROW MCU_buffer[D_MAX_BLOCKS_IN_MCU];
47 /* Temporary workspace for one MCU */
50 #ifdef D_MULTISCAN_FILES_SUPPORTED
51 /* In multi-pass modes, we need a virtual block array for each component. */
52 jvirt_barray_ptr whole_image[MAX_COMPONENTS];
55 #ifdef BLOCK_SMOOTHING_SUPPORTED
56 /* When doing block smoothing, we latch coefficient Al values here */
58 #define SAVED_COEFS 10 /* we save coef_bits[0..9] */
62 typedef my_coef_controller *my_coef_ptr;
66 start_iMCU_row(j_decompress_ptr cinfo)
67 /* Reset within-iMCU-row counters for a new row (input side) */
69 my_coef_ptr coef = (my_coef_ptr)cinfo->coef;
71 /* In an interleaved scan, an MCU row is the same as an iMCU row.
72 * In a noninterleaved scan, an iMCU row has v_samp_factor MCU rows.
73 * But at the bottom of the image, process only what's left.
75 if (cinfo->comps_in_scan > 1) {
76 coef->MCU_rows_per_iMCU_row = 1;
78 if (cinfo->input_iMCU_row < (cinfo->total_iMCU_rows - 1))
79 coef->MCU_rows_per_iMCU_row = cinfo->cur_comp_info[0]->v_samp_factor;
81 coef->MCU_rows_per_iMCU_row = cinfo->cur_comp_info[0]->last_row_height;
85 coef->MCU_vert_offset = 0;
88 #endif /* BITS_IN_JSAMPLE != 16 || defined(D_LOSSLESS_SUPPORTED) */