/*
 * jddctmgr.c
 *
 * Copyright (C) 1994-1995, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains the inverse-DCT management logic.
 * This code selects a particular IDCT implementation to be used,
 * and it performs related housekeeping chores.  No code in this file
 * is executed per IDCT step, only during output pass setup.
 *
 * Note that the IDCT routines are responsible for performing coefficient
 * dequantization as well as the IDCT proper.  This module sets up the
 * dequantization multiplier table needed by the IDCT routine.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jdct.h"        /* Private declarations for DCT subsystem */


/*
 * The decompressor input side (jdinput.c) saves away the appropriate
 * quantization table for each component at the start of the first scan
 * involving that component.  (This is necessary in order to correctly
 * decode files that reuse Q-table slots.)
 * When we are ready to make an output pass, the saved Q-table is converted
 * to a multiplier table that will actually be used by the IDCT routine.
 * The multiplier table contents are IDCT-method-dependent.  To support
 * application changes in IDCT method between scans, we can remake the
 * multiplier tables if necessary.
 * In buffered-image mode, the first output pass may occur before any data
 * has been seen for some components, and thus before their Q-tables have
 * been saved away.  To handle this case, multiplier tables are preset
 * to zeroes; the result of the IDCT will be a neutral gray level.
 */


/* Private subobject for this module */

typedef struct {
	struct jpeg_inverse_dct pub; /* public fields */

	/* This array contains the IDCT method code that each multiplier table
	 * is currently set up for, or -1 if it's not yet set up.
	 * The actual multiplier tables are pointed to by dct_table in the
	 * per-component comp_info structures.
	 */
	int cur_method[MAX_COMPONENTS];
} my_idct_controller;

typedef my_idct_controller * my_idct_ptr;


/* Allocated multiplier tables: big enough for any supported variant */

typedef union {
	ISLOW_MULT_TYPE islow_array[DCTSIZE2];
#ifdef DCT_IFAST_SUPPORTED
	IFAST_MULT_TYPE ifast_array[DCTSIZE2];
#endif
#ifdef DCT_FLOAT_SUPPORTED
	FLOAT_MULT_TYPE float_array[DCTSIZE2];
#endif
} multiplier_table;


/* The current scaled-IDCT routines require ISLOW-style multiplier tables,
 * so be sure to compile that code if either ISLOW or SCALING is requested.
 */
#ifdef DCT_ISLOW_SUPPORTED
#define PROVIDE_ISLOW_TABLES
#else
#ifdef IDCT_SCALING_SUPPORTED
#define PROVIDE_ISLOW_TABLES
#endif
#endif


/*
 * Prepare for an output pass.
 * Here we select the proper IDCT routine for each component and build
 * a matching multiplier table.
 */

METHODDEF void
start_pass( j_decompress_ptr cinfo ) {
	my_idct_ptr idct = (my_idct_ptr) cinfo->idct;
	int ci, i;
	jpeg_component_info *compptr;
	int method = 0;
	inverse_DCT_method_ptr method_ptr = NULL;
	JQUANT_TBL * qtbl;

	for ( ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
		  ci++, compptr++ ) {
		/* Select the proper IDCT routine for this component's scaling */
		switch ( compptr->DCT_scaled_size ) {
#ifdef IDCT_SCALING_SUPPORTED
		case 1:
			method_ptr = jpeg_idct_1x1;
			method = JDCT_ISLOW; /* jidctred uses islow-style table */
			break;
		case 2:
			method_ptr = jpeg_idct_2x2;
			method = JDCT_ISLOW; /* jidctred uses islow-style table */
			break;
		case 4:
			method_ptr = jpeg_idct_4x4;
			method = JDCT_ISLOW; /* jidctred uses islow-style table */
			break;
#endif
		case DCTSIZE:
			switch ( cinfo->dct_method ) {
#ifdef DCT_ISLOW_SUPPORTED
			case JDCT_ISLOW:
				method_ptr = jpeg_idct_islow;
				method = JDCT_ISLOW;
				break;
#endif
#ifdef DCT_IFAST_SUPPORTED
			case JDCT_IFAST:
				method_ptr = jpeg_idct_ifast;
				method = JDCT_IFAST;
				break;
#endif
#ifdef DCT_FLOAT_SUPPORTED
			case JDCT_FLOAT:
				method_ptr = jpeg_idct_float;
				method = JDCT_FLOAT;
				break;
#endif
			default:
				ERREXIT( cinfo, JERR_NOT_COMPILED );
				break;
			}
			break;
		default:
			ERREXIT1( cinfo, JERR_BAD_DCTSIZE, compptr->DCT_scaled_size );
			break;
		}
		idct->pub.inverse_DCT[ci] = method_ptr;
		/* Create multiplier table from quant table.
		 * However, we can skip this if the component is uninteresting
		 * or if we already built the table.  Also, if no quant table
		 * has yet been saved for the component, we leave the
		 * multiplier table all-zero; we'll be reading zeroes from the
		 * coefficient controller's buffer anyway.
		 */
		if ( !compptr->component_needed || idct->cur_method[ci] == method ) {
			continue;
		}
		qtbl = compptr->quant_table;
		if ( qtbl == NULL ) { /* happens if no data yet for component */
			continue;
		}
		idct->cur_method[ci] = method;
		switch ( method ) {
#ifdef PROVIDE_ISLOW_TABLES
		case JDCT_ISLOW:
		{
			/* For LL&M IDCT method, multipliers are equal to raw quantization
			 * coefficients, but are stored in natural order as ints.
			 */
			ISLOW_MULT_TYPE * ismtbl = (ISLOW_MULT_TYPE *) compptr->dct_table;
			for ( i = 0; i < DCTSIZE2; i++ ) {
				ismtbl[i] = (ISLOW_MULT_TYPE) qtbl->quantval[jpeg_zigzag_order[i]];
			}
		}
		break;
#endif
#ifdef DCT_IFAST_SUPPORTED
		case JDCT_IFAST:
		{
			/* For AA&N IDCT method, multipliers are equal to quantization
			 * coefficients scaled by scalefactor[row]*scalefactor[col], where
			 *   scalefactor[0] = 1
			 *   scalefactor[k] = cos(k*PI/16) * sqrt(2)    for k=1..7
			 * For integer operation, the multiplier table is to be scaled by
			 * IFAST_SCALE_BITS.  The multipliers are stored in natural order.
			 */
			IFAST_MULT_TYPE * ifmtbl = (IFAST_MULT_TYPE *) compptr->dct_table;
#define CONST_BITS 14
			static const INT16 aanscales[DCTSIZE2] = {
				/* precomputed values scaled up by 14 bits */
				16384, 22725, 21407, 19266, 16384, 12873,  8867,  4520,
				22725, 31521, 29692, 26722, 22725, 17855, 12299,  6270,
				21407, 29692, 27969, 25172, 21407, 16819, 11585,  5906,
				19266, 26722, 25172, 22654, 19266, 15137, 10426,  5315,
				16384, 22725, 21407, 19266, 16384, 12873,  8867,  4520,
				12873, 17855, 16819, 15137, 12873, 10114,  6967,  3552,
				8867, 12299, 11585, 10426,  8867,  6967,  4799,  2446,
				4520,  6270,  5906,  5315,  4520,  3552,  2446,  1247
			};
			SHIFT_TEMPS

			for ( i = 0; i < DCTSIZE2; i++ ) {
				ifmtbl[i] = (IFAST_MULT_TYPE)
							DESCALE( MULTIPLY16V16( (INT32) qtbl->quantval[jpeg_zigzag_order[i]],
													(INT32) aanscales[i] ),
									 CONST_BITS - IFAST_SCALE_BITS );
			}
		}
		break;
#endif
#ifdef DCT_FLOAT_SUPPORTED
		case JDCT_FLOAT:
		{
			/* For float AA&N IDCT method, multipliers are equal to quantization
			 * coefficients scaled by scalefactor[row]*scalefactor[col], where
			 *   scalefactor[0] = 1
			 *   scalefactor[k] = cos(k*PI/16) * sqrt(2)    for k=1..7
			 * The multipliers are stored in natural order.
			 */
			FLOAT_MULT_TYPE * fmtbl = (FLOAT_MULT_TYPE *) compptr->dct_table;
			int row, col;
			static const double aanscalefactor[DCTSIZE] = {
				1.0, 1.387039845, 1.306562965, 1.175875602,
				1.0, 0.785694958, 0.541196100, 0.275899379
			};

			i = 0;
			for ( row = 0; row < DCTSIZE; row++ ) {
				for ( col = 0; col < DCTSIZE; col++ ) {
					fmtbl[i] = (FLOAT_MULT_TYPE)
					  ( (double) qtbl->quantval[jpeg_zigzag_order[i]] *
					  aanscalefactor[row] * aanscalefactor[col] );
					i++;
				}
			}
		}
		break;
#endif
		default:
			ERREXIT( cinfo, JERR_NOT_COMPILED );
			break;
		}
	}
}


/*
 * Initialize IDCT manager.
 */

GLOBAL void
jinit_inverse_dct( j_decompress_ptr cinfo ) {
	my_idct_ptr idct;
	int ci;
	jpeg_component_info *compptr;

	idct = (my_idct_ptr)
				( *cinfo->mem->alloc_small ) ( (j_common_ptr) cinfo, JPOOL_IMAGE,
											   SIZEOF( my_idct_controller ) );
	cinfo->idct = (struct jpeg_inverse_dct *) idct;
	idct->pub.start_pass = start_pass;

	for ( ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
		  ci++, compptr++ ) {
		/* Allocate and pre-zero a multiplier table for each component */
		compptr->dct_table =
			( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE,
										  SIZEOF( multiplier_table ) );
		MEMZERO( compptr->dct_table, SIZEOF( multiplier_table ) );
		/* Mark multiplier table not yet set up for any method */
		idct->cur_method[ci] = -1;
	}
}
