CoCalc -- jidctint.c

GitHub Repository: PojavLauncherTeam/mobile
Path: blob/master/src/java.desktop/share/native/libjavajpeg/jidctint.c
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/*
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 * reserved comment block
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 * DO NOT REMOVE OR ALTER!
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 */
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/*
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 * jidctint.c
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 *
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 * Copyright (C) 1991-1998, Thomas G. Lane.
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 * This file is part of the Independent JPEG Group's software.
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 * For conditions of distribution and use, see the accompanying README file.
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 *
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 * This file contains a slow-but-accurate integer implementation of the
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 * inverse DCT (Discrete Cosine Transform).  In the IJG code, this routine
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 * must also perform dequantization of the input coefficients.
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 *
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 * A 2-D IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT
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 * on each row (or vice versa, but it's more convenient to emit a row at
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 * a time).  Direct algorithms are also available, but they are much more
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 * complex and seem not to be any faster when reduced to code.
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 *
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 * This implementation is based on an algorithm described in
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 *   C. Loeffler, A. Ligtenberg and G. Moschytz, "Practical Fast 1-D DCT
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 *   Algorithms with 11 Multiplications", Proc. Int'l. Conf. on Acoustics,
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 *   Speech, and Signal Processing 1989 (ICASSP '89), pp. 988-991.
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 * The primary algorithm described there uses 11 multiplies and 29 adds.
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 * We use their alternate method with 12 multiplies and 32 adds.
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 * The advantage of this method is that no data path contains more than one
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 * multiplication; this allows a very simple and accurate implementation in
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 * scaled fixed-point arithmetic, with a minimal number of shifts.
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 */
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#define JPEG_INTERNALS
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#include "jinclude.h"
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#include "jpeglib.h"
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#include "jdct.h"               /* Private declarations for DCT subsystem */
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#ifdef DCT_ISLOW_SUPPORTED
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/*
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 * This module is specialized to the case DCTSIZE = 8.
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 */
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#if DCTSIZE != 8
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  Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
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#endif
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/*
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 * The poop on this scaling stuff is as follows:
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 *
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 * Each 1-D IDCT step produces outputs which are a factor of sqrt(N)
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 * larger than the true IDCT outputs.  The final outputs are therefore
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 * a factor of N larger than desired; since N=8 this can be cured by
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 * a simple right shift at the end of the algorithm.  The advantage of
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 * this arrangement is that we save two multiplications per 1-D IDCT,
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 * because the y0 and y4 inputs need not be divided by sqrt(N).
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 *
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 * We have to do addition and subtraction of the integer inputs, which
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 * is no problem, and multiplication by fractional constants, which is
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 * a problem to do in integer arithmetic.  We multiply all the constants
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 * by CONST_SCALE and convert them to integer constants (thus retaining
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 * CONST_BITS bits of precision in the constants).  After doing a
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 * multiplication we have to divide the product by CONST_SCALE, with proper
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 * rounding, to produce the correct output.  This division can be done
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 * cheaply as a right shift of CONST_BITS bits.  We postpone shifting
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 * as long as possible so that partial sums can be added together with
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 * full fractional precision.
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 *
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 * The outputs of the first pass are scaled up by PASS1_BITS bits so that
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 * they are represented to better-than-integral precision.  These outputs
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 * require BITS_IN_JSAMPLE + PASS1_BITS + 3 bits; this fits in a 16-bit word
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 * with the recommended scaling.  (To scale up 12-bit sample data further, an
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 * intermediate INT32 array would be needed.)
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 *
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 * To avoid overflow of the 32-bit intermediate results in pass 2, we must
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 * have BITS_IN_JSAMPLE + CONST_BITS + PASS1_BITS <= 26.  Error analysis
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 * shows that the values given below are the most effective.
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 */
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#if BITS_IN_JSAMPLE == 8
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#define CONST_BITS  13
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#define PASS1_BITS  2
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#else
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#define CONST_BITS  13
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#define PASS1_BITS  1           /* lose a little precision to avoid overflow */
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#endif
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/* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
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 * causing a lot of useless floating-point operations at run time.
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 * To get around this we use the following pre-calculated constants.
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 * If you change CONST_BITS you may want to add appropriate values.
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 * (With a reasonable C compiler, you can just rely on the FIX() macro...)
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 */
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#if CONST_BITS == 13
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#define FIX_0_298631336  ((INT32)  2446)        /* FIX(0.298631336) */
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#define FIX_0_390180644  ((INT32)  3196)        /* FIX(0.390180644) */
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#define FIX_0_541196100  ((INT32)  4433)        /* FIX(0.541196100) */
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#define FIX_0_765366865  ((INT32)  6270)        /* FIX(0.765366865) */
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#define FIX_0_899976223  ((INT32)  7373)        /* FIX(0.899976223) */
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#define FIX_1_175875602  ((INT32)  9633)        /* FIX(1.175875602) */
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#define FIX_1_501321110  ((INT32)  12299)       /* FIX(1.501321110) */
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#define FIX_1_847759065  ((INT32)  15137)       /* FIX(1.847759065) */
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#define FIX_1_961570560  ((INT32)  16069)       /* FIX(1.961570560) */
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#define FIX_2_053119869  ((INT32)  16819)       /* FIX(2.053119869) */
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#define FIX_2_562915447  ((INT32)  20995)       /* FIX(2.562915447) */
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#define FIX_3_072711026  ((INT32)  25172)       /* FIX(3.072711026) */
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#else
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#define FIX_0_298631336  FIX(0.298631336)
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#define FIX_0_390180644  FIX(0.390180644)
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#define FIX_0_541196100  FIX(0.541196100)
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#define FIX_0_765366865  FIX(0.765366865)
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#define FIX_0_899976223  FIX(0.899976223)
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#define FIX_1_175875602  FIX(1.175875602)
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#define FIX_1_501321110  FIX(1.501321110)
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#define FIX_1_847759065  FIX(1.847759065)
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#define FIX_1_961570560  FIX(1.961570560)
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#define FIX_2_053119869  FIX(2.053119869)
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#define FIX_2_562915447  FIX(2.562915447)
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#define FIX_3_072711026  FIX(3.072711026)
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#endif
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/* Multiply an INT32 variable by an INT32 constant to yield an INT32 result.
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 * For 8-bit samples with the recommended scaling, all the variable
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 * and constant values involved are no more than 16 bits wide, so a
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 * 16x16->32 bit multiply can be used instead of a full 32x32 multiply.
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 * For 12-bit samples, a full 32-bit multiplication will be needed.
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 */
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#if BITS_IN_JSAMPLE == 8
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#define MULTIPLY(var,const)  MULTIPLY16C16(var,const)
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#else
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#define MULTIPLY(var,const)  ((var) * (const))
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#endif
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/* Dequantize a coefficient by multiplying it by the multiplier-table
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 * entry; produce an int result.  In this module, both inputs and result
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 * are 16 bits or less, so either int or short multiply will work.
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 */
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#define DEQUANTIZE(coef,quantval)  (((ISLOW_MULT_TYPE) (coef)) * (quantval))
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/*
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 * Perform dequantization and inverse DCT on one block of coefficients.
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 */
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GLOBAL(void)
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jpeg_idct_islow (j_decompress_ptr cinfo, jpeg_component_info * compptr,
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                 JCOEFPTR coef_block,
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                 JSAMPARRAY output_buf, JDIMENSION output_col)
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{
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  INT32 tmp0, tmp1, tmp2, tmp3;
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  INT32 tmp10, tmp11, tmp12, tmp13;
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  INT32 z1, z2, z3, z4, z5;
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  JCOEFPTR inptr;
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  ISLOW_MULT_TYPE * quantptr;
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  int * wsptr;
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  JSAMPROW outptr;
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  JSAMPLE *range_limit = IDCT_range_limit(cinfo);
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  int ctr;
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  int workspace[DCTSIZE2];      /* buffers data between passes */
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  SHIFT_TEMPS
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  /* Pass 1: process columns from input, store into work array. */
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  /* Note results are scaled up by sqrt(8) compared to a true IDCT; */
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  /* furthermore, we scale the results by 2**PASS1_BITS. */
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  inptr = coef_block;
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  quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
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  wsptr = workspace;
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  for (ctr = DCTSIZE; ctr > 0; ctr--) {
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    /* Due to quantization, we will usually find that many of the input
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     * coefficients are zero, especially the AC terms.  We can exploit this
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     * by short-circuiting the IDCT calculation for any column in which all
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     * the AC terms are zero.  In that case each output is equal to the
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     * DC coefficient (with scale factor as needed).
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     * With typical images and quantization tables, half or more of the
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     * column DCT calculations can be simplified this way.
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     */
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    if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&
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        inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*4] == 0 &&
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        inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*6] == 0 &&
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        inptr[DCTSIZE*7] == 0) {
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      /* AC terms all zero */
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      int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS;
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      wsptr[DCTSIZE*0] = dcval;
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      wsptr[DCTSIZE*1] = dcval;
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      wsptr[DCTSIZE*2] = dcval;
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      wsptr[DCTSIZE*3] = dcval;
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      wsptr[DCTSIZE*4] = dcval;
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      wsptr[DCTSIZE*5] = dcval;
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      wsptr[DCTSIZE*6] = dcval;
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      wsptr[DCTSIZE*7] = dcval;
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      inptr++;                  /* advance pointers to next column */
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      quantptr++;
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      wsptr++;
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      continue;
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    }
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    /* Even part: reverse the even part of the forward DCT. */
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    /* The rotator is sqrt(2)*c(-6). */
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    z2 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
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    z3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
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    z1 = MULTIPLY(z2 + z3, FIX_0_541196100);
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    tmp2 = z1 + MULTIPLY(z3, - FIX_1_847759065);
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    tmp3 = z1 + MULTIPLY(z2, FIX_0_765366865);
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    z2 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
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    z3 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]);
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    tmp0 = (z2 + z3) << CONST_BITS;
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    tmp1 = (z2 - z3) << CONST_BITS;
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    tmp10 = tmp0 + tmp3;
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    tmp13 = tmp0 - tmp3;
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    tmp11 = tmp1 + tmp2;
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    tmp12 = tmp1 - tmp2;
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    /* Odd part per figure 8; the matrix is unitary and hence its
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     * transpose is its inverse.  i0..i3 are y7,y5,y3,y1 respectively.
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     */
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    tmp0 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
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    tmp1 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
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    tmp2 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
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    tmp3 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
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    z1 = tmp0 + tmp3;
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    z2 = tmp1 + tmp2;
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    z3 = tmp0 + tmp2;
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    z4 = tmp1 + tmp3;
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    z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */
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    tmp0 = MULTIPLY(tmp0, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */
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    tmp1 = MULTIPLY(tmp1, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */
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    tmp2 = MULTIPLY(tmp2, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */
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    tmp3 = MULTIPLY(tmp3, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */
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    z1 = MULTIPLY(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */
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    z2 = MULTIPLY(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
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    z3 = MULTIPLY(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
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    z4 = MULTIPLY(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */
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    z3 += z5;
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    z4 += z5;
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    tmp0 += z1 + z3;
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    tmp1 += z2 + z4;
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    tmp2 += z2 + z3;
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    tmp3 += z1 + z4;
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    /* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */
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    wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp3, CONST_BITS-PASS1_BITS);
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    wsptr[DCTSIZE*7] = (int) DESCALE(tmp10 - tmp3, CONST_BITS-PASS1_BITS);
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    wsptr[DCTSIZE*1] = (int) DESCALE(tmp11 + tmp2, CONST_BITS-PASS1_BITS);
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    wsptr[DCTSIZE*6] = (int) DESCALE(tmp11 - tmp2, CONST_BITS-PASS1_BITS);
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    wsptr[DCTSIZE*2] = (int) DESCALE(tmp12 + tmp1, CONST_BITS-PASS1_BITS);
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    wsptr[DCTSIZE*5] = (int) DESCALE(tmp12 - tmp1, CONST_BITS-PASS1_BITS);
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    wsptr[DCTSIZE*3] = (int) DESCALE(tmp13 + tmp0, CONST_BITS-PASS1_BITS);
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    wsptr[DCTSIZE*4] = (int) DESCALE(tmp13 - tmp0, CONST_BITS-PASS1_BITS);
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    inptr++;                    /* advance pointers to next column */
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    quantptr++;
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    wsptr++;
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  }
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  /* Pass 2: process rows from work array, store into output array. */
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  /* Note that we must descale the results by a factor of 8 == 2**3, */
278
  /* and also undo the PASS1_BITS scaling. */
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280
  wsptr = workspace;
281
  for (ctr = 0; ctr < DCTSIZE; ctr++) {
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    outptr = output_buf[ctr] + output_col;
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    /* Rows of zeroes can be exploited in the same way as we did with columns.
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     * However, the column calculation has created many nonzero AC terms, so
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     * the simplification applies less often (typically 5% to 10% of the time).
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     * On machines with very fast multiplication, it's possible that the
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     * test takes more time than it's worth.  In that case this section
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     * may be commented out.
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     */
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#ifndef NO_ZERO_ROW_TEST
292
    if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && wsptr[4] == 0 &&
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        wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) {
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      /* AC terms all zero */
295
      JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3)
296
                                  & RANGE_MASK];
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298
      outptr[0] = dcval;
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      outptr[1] = dcval;
300
      outptr[2] = dcval;
301
      outptr[3] = dcval;
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      outptr[4] = dcval;
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      outptr[5] = dcval;
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      outptr[6] = dcval;
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      outptr[7] = dcval;
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307
      wsptr += DCTSIZE;         /* advance pointer to next row */
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      continue;
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    }
310
#endif
311

312
    /* Even part: reverse the even part of the forward DCT. */
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    /* The rotator is sqrt(2)*c(-6). */
314

315
    z2 = (INT32) wsptr[2];
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    z3 = (INT32) wsptr[6];
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    z1 = MULTIPLY(z2 + z3, FIX_0_541196100);
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    tmp2 = z1 + MULTIPLY(z3, - FIX_1_847759065);
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    tmp3 = z1 + MULTIPLY(z2, FIX_0_765366865);
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    tmp0 = ((INT32) wsptr[0] + (INT32) wsptr[4]) << CONST_BITS;
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    tmp1 = ((INT32) wsptr[0] - (INT32) wsptr[4]) << CONST_BITS;
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325
    tmp10 = tmp0 + tmp3;
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    tmp13 = tmp0 - tmp3;
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    tmp11 = tmp1 + tmp2;
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    tmp12 = tmp1 - tmp2;
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    /* Odd part per figure 8; the matrix is unitary and hence its
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     * transpose is its inverse.  i0..i3 are y7,y5,y3,y1 respectively.
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     */
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    tmp0 = (INT32) wsptr[7];
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    tmp1 = (INT32) wsptr[5];
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    tmp2 = (INT32) wsptr[3];
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    tmp3 = (INT32) wsptr[1];
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    z1 = tmp0 + tmp3;
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    z2 = tmp1 + tmp2;
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    z3 = tmp0 + tmp2;
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    z4 = tmp1 + tmp3;
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    z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */
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    tmp0 = MULTIPLY(tmp0, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */
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    tmp1 = MULTIPLY(tmp1, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */
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    tmp2 = MULTIPLY(tmp2, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */
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    tmp3 = MULTIPLY(tmp3, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */
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    z1 = MULTIPLY(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */
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    z2 = MULTIPLY(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
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    z3 = MULTIPLY(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
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    z4 = MULTIPLY(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */
353

354
    z3 += z5;
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    z4 += z5;
356

357
    tmp0 += z1 + z3;
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    tmp1 += z2 + z4;
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    tmp2 += z2 + z3;
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    tmp3 += z1 + z4;
361

362
    /* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */
363

364
    outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp3,
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                                          CONST_BITS+PASS1_BITS+3)
366
                            & RANGE_MASK];
367
    outptr[7] = range_limit[(int) DESCALE(tmp10 - tmp3,
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                                          CONST_BITS+PASS1_BITS+3)
369
                            & RANGE_MASK];
370
    outptr[1] = range_limit[(int) DESCALE(tmp11 + tmp2,
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                                          CONST_BITS+PASS1_BITS+3)
372
                            & RANGE_MASK];
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    outptr[6] = range_limit[(int) DESCALE(tmp11 - tmp2,
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                                          CONST_BITS+PASS1_BITS+3)
375
                            & RANGE_MASK];
376
    outptr[2] = range_limit[(int) DESCALE(tmp12 + tmp1,
377
                                          CONST_BITS+PASS1_BITS+3)
378
                            & RANGE_MASK];
379
    outptr[5] = range_limit[(int) DESCALE(tmp12 - tmp1,
380
                                          CONST_BITS+PASS1_BITS+3)
381
                            & RANGE_MASK];
382
    outptr[3] = range_limit[(int) DESCALE(tmp13 + tmp0,
383
                                          CONST_BITS+PASS1_BITS+3)
384
                            & RANGE_MASK];
385
    outptr[4] = range_limit[(int) DESCALE(tmp13 - tmp0,
386
                                          CONST_BITS+PASS1_BITS+3)
387
                            & RANGE_MASK];
388

389
    wsptr += DCTSIZE;           /* advance pointer to next row */
390
  }
391
}
392

393
#endif /* DCT_ISLOW_SUPPORTED */
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