    /*
     * jdmerge.c
     *
     * Copyright (C) 1994-1996, Thomas G. Lane.
     * Modified 2013-2020 by Guido Vollbeding.
     * 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 code for merged upsampling/color conversion.
     *
     * This file combines functions from jdsample.c and jdcolor.c;
     * read those files first to understand what's going on.
     *
     * When the chroma components are to be upsampled by simple replication
     * (ie, box filtering), we can save some work in color conversion by
     * calculating all the output pixels corresponding to a pair of chroma
     * samples at one time.  In the conversion equations
     *	R = Y           + K1 * Cr
     *	G = Y + K2 * Cb + K3 * Cr
     *	B = Y + K4 * Cb
     * only the Y term varies among the group of pixels corresponding to a pair
     * of chroma samples, so the rest of the terms can be calculated just once.
     * At typical sampling ratios, this eliminates half or three-quarters of the
     * multiplications needed for color conversion.
     *
     * This file currently provides implementations for the following cases:
     *	YCC => RGB color conversion only (YCbCr or BG_YCC).
     *	Sampling ratios of 2h1v or 2h2v.
     *	No scaling needed at upsample time.
     *	Corner-aligned (non-CCIR601) sampling alignment.
     * Other special cases could be added, but in most applications these are
     * the only common cases.  (For uncommon cases we fall back on the more
     * general code in jdsample.c and jdcolor.c.)
     */

    #define JPEG_INTERNALS
    #include "jinclude.h"
    #include "jpeglib.h"

    #ifdef UPSAMPLE_MERGING_SUPPORTED

    #if RANGE_BITS < 2
      /* Deliberate syntax err */
      Sorry, this code requires 2 or more range extension bits.
    #endif

    /* Private subobject */

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

      /* Pointer to routine to do actual upsampling/conversion of one row group */
      JMETHOD(void, upmethod, (j_decompress_ptr cinfo,
    			   JSAMPIMAGE input_buf, JDIMENSION in_row_group_ctr,
    			   JSAMPARRAY output_buf));

      /* Private state for YCC->RGB conversion */
      int * Cr_r_tab;		/* => table for Cr to R conversion */
      int * Cb_b_tab;		/* => table for Cb to B conversion */
      INT32 * Cr_g_tab;		/* => table for Cr to G conversion */
      INT32 * Cb_g_tab;		/* => table for Cb to G conversion */

      /* For 2:1 vertical sampling, we produce two output rows at a time.
       * We need a "spare" row buffer to hold the second output row if the
       * application provides just a one-row buffer; we also use the spare
       * to discard the dummy last row if the image height is odd.
       */
      JSAMPROW spare_row;
      boolean spare_full;		/* T if spare buffer is occupied */

      JDIMENSION out_row_width;	/* samples per output row */
      JDIMENSION rows_to_go;	/* counts rows remaining in image */
    } my_upsampler;

    typedef my_upsampler * my_upsample_ptr;

    #define SCALEBITS	16	/* speediest right-shift on some machines */
    #define ONE_HALF	((INT32) 1 << (SCALEBITS-1))
    #define FIX(x)		((INT32) ((x) * (1L<<SCALEBITS) + 0.5))

    /*
     * Initialize tables for YCbCr->RGB and BG_YCC->RGB colorspace conversion.
     * This is taken directly from jdcolor.c; see that file for more info.
     */

    LOCAL(void)
    build_ycc_rgb_table (j_decompress_ptr cinfo)
    /* Normal case, sYCC */
    {
      my_upsample_ptr upsample = (my_upsample_ptr) cinfo->upsample;
      int i;
      INT32 x;
      SHIFT_TEMPS

      upsample->Cr_r_tab = (int *) (*cinfo->mem->alloc_small)
        ((j_common_ptr) cinfo, JPOOL_IMAGE, (MAXJSAMPLE+1) * SIZEOF(int));
      upsample->Cb_b_tab = (int *) (*cinfo->mem->alloc_small)
        ((j_common_ptr) cinfo, JPOOL_IMAGE, (MAXJSAMPLE+1) * SIZEOF(int));
      upsample->Cr_g_tab = (INT32 *) (*cinfo->mem->alloc_small)
        ((j_common_ptr) cinfo, JPOOL_IMAGE, (MAXJSAMPLE+1) * SIZEOF(INT32));
      upsample->Cb_g_tab = (INT32 *) (*cinfo->mem->alloc_small)
        ((j_common_ptr) cinfo, JPOOL_IMAGE, (MAXJSAMPLE+1) * SIZEOF(INT32));

      for (i = 0, x = -CENTERJSAMPLE; i <= MAXJSAMPLE; i++, x++) {
        /* i is the actual input pixel value, in the range 0..MAXJSAMPLE */
        /* The Cb or Cr value we are thinking of is x = i - CENTERJSAMPLE */
        /* Cr=>R value is nearest int to 1.402 * x */
        upsample->Cr_r_tab[i] = (int) DESCALE(FIX(1.402) * x, SCALEBITS);
        /* Cb=>B value is nearest int to 1.772 * x */
        upsample->Cb_b_tab[i] = (int) DESCALE(FIX(1.772) * x, SCALEBITS);
        /* Cr=>G value is scaled-up -0.714136286 * x */
        upsample->Cr_g_tab[i] = (- FIX(0.714136286)) * x;
        /* Cb=>G value is scaled-up -0.344136286 * x */
        /* We also add in ONE_HALF so that need not do it in inner loop */
        upsample->Cb_g_tab[i] = (- FIX(0.344136286)) * x + ONE_HALF;
      }
    }

    LOCAL(void)
    build_bg_ycc_rgb_table (j_decompress_ptr cinfo)
    /* Wide gamut case, bg-sYCC */
    {
      my_upsample_ptr upsample = (my_upsample_ptr) cinfo->upsample;
      int i;
      INT32 x;
      SHIFT_TEMPS

      upsample->Cr_r_tab = (int *) (*cinfo->mem->alloc_small)
        ((j_common_ptr) cinfo, JPOOL_IMAGE, (MAXJSAMPLE+1) * SIZEOF(int));
      upsample->Cb_b_tab = (int *) (*cinfo->mem->alloc_small)
        ((j_common_ptr) cinfo, JPOOL_IMAGE, (MAXJSAMPLE+1) * SIZEOF(int));
      upsample->Cr_g_tab = (INT32 *) (*cinfo->mem->alloc_small)
        ((j_common_ptr) cinfo, JPOOL_IMAGE, (MAXJSAMPLE+1) * SIZEOF(INT32));
      upsample->Cb_g_tab = (INT32 *) (*cinfo->mem->alloc_small)
        ((j_common_ptr) cinfo, JPOOL_IMAGE, (MAXJSAMPLE+1) * SIZEOF(INT32));

      for (i = 0, x = -CENTERJSAMPLE; i <= MAXJSAMPLE; i++, x++) {
        /* i is the actual input pixel value, in the range 0..MAXJSAMPLE */
        /* The Cb or Cr value we are thinking of is x = i - CENTERJSAMPLE */
        /* Cr=>R value is nearest int to 2.804 * x */
        upsample->Cr_r_tab[i] = (int) DESCALE(FIX(2.804) * x, SCALEBITS);
        /* Cb=>B value is nearest int to 3.544 * x */
        upsample->Cb_b_tab[i] = (int) DESCALE(FIX(3.544) * x, SCALEBITS);
        /* Cr=>G value is scaled-up -1.428272572 * x */
        upsample->Cr_g_tab[i] = (- FIX(1.428272572)) * x;
        /* Cb=>G value is scaled-up -0.688272572 * x */
        /* We also add in ONE_HALF so that need not do it in inner loop */
        upsample->Cb_g_tab[i] = (- FIX(0.688272572)) * x + ONE_HALF;
      }
    }

    /*
     * Initialize for an upsampling pass.
     */

    METHODDEF(void)
    start_pass_merged_upsample (j_decompress_ptr cinfo)
    {
      my_upsample_ptr upsample = (my_upsample_ptr) cinfo->upsample;

      /* Mark the spare buffer empty */
      upsample->spare_full = FALSE;
      /* Initialize total-height counter for detecting bottom of image */
      upsample->rows_to_go = cinfo->output_height;
    }

    /*
     * Control routine to do upsampling (and color conversion).
     *
     * The control routine just handles the row buffering considerations.
     */

    METHODDEF(void)
    merged_2v_upsample (j_decompress_ptr cinfo,
    		    JSAMPIMAGE input_buf, JDIMENSION *in_row_group_ctr,
    		    JDIMENSION in_row_groups_avail,
    		    JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
    		    JDIMENSION out_rows_avail)
    /* 2:1 vertical sampling case: may need a spare row. */
    {
      my_upsample_ptr upsample = (my_upsample_ptr) cinfo->upsample;
      JSAMPROW work_ptrs[2];
      JDIMENSION num_rows;		/* number of rows returned to caller */

      if (upsample->spare_full) {
        /* If we have a spare row saved from a previous cycle, just return it. */
        jcopy_sample_rows(& upsample->spare_row, output_buf + *out_row_ctr,
    		      1, upsample->out_row_width);
        num_rows = 1;
        upsample->spare_full = FALSE;
      } else {
        /* Figure number of rows to return to caller. */
        num_rows = 2;
        /* Not more than the distance to the end of the image. */
        if (num_rows > upsample->rows_to_go)
          num_rows = upsample->rows_to_go;
        /* And not more than what the client can accept: */
        out_rows_avail -= *out_row_ctr;
        if (num_rows > out_rows_avail)
          num_rows = out_rows_avail;
        /* Create output pointer array for upsampler. */
        work_ptrs[0] = output_buf[*out_row_ctr];
        if (num_rows > 1) {
          work_ptrs[1] = output_buf[*out_row_ctr + 1];
        } else {
          work_ptrs[1] = upsample->spare_row;
          upsample->spare_full = TRUE;
        }
        /* Now do the upsampling. */
        (*upsample->upmethod) (cinfo, input_buf, *in_row_group_ctr, work_ptrs);
      }

      /* Adjust counts */
      *out_row_ctr += num_rows;
      upsample->rows_to_go -= num_rows;
      /* When the buffer is emptied, declare this input row group consumed */
      if (! upsample->spare_full)
        (*in_row_group_ctr)++;
    }

    METHODDEF(void)
    merged_1v_upsample (j_decompress_ptr cinfo,
    		    JSAMPIMAGE input_buf, JDIMENSION *in_row_group_ctr,
    		    JDIMENSION in_row_groups_avail,
    		    JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
    		    JDIMENSION out_rows_avail)
    /* 1:1 vertical sampling case: much easier, never need a spare row. */
    {
      my_upsample_ptr upsample = (my_upsample_ptr) cinfo->upsample;

      /* Just do the upsampling. */
      (*upsample->upmethod) (cinfo, input_buf, *in_row_group_ctr,
    			 output_buf + *out_row_ctr);
      /* Adjust counts */
      (*out_row_ctr)++;
      (*in_row_group_ctr)++;
    }

    /*
     * These are the routines invoked by the control routines to do
     * the actual upsampling/conversion.  One row group is processed per call.
     *
     * Note: since we may be writing directly into application-supplied buffers,
     * we have to be honest about the output width; we can't assume the buffer
     * has been rounded up to an even width.
     */

    /*
     * Upsample and color convert for the case of 2:1 horizontal and 1:1 vertical.
     */

    METHODDEF(void)
    h2v1_merged_upsample (j_decompress_ptr cinfo,
    		      JSAMPIMAGE input_buf, JDIMENSION in_row_group_ctr,
    		      JSAMPARRAY output_buf)
    {
      my_upsample_ptr upsample = (my_upsample_ptr) cinfo->upsample;
      register int y, cred, cgreen, cblue;
      int cb, cr;
      register JSAMPROW outptr;
      JSAMPROW inptr0, inptr1, inptr2;
      JDIMENSION col;
      /* copy these pointers into registers if possible */
      register JSAMPLE * range_limit = cinfo->sample_range_limit;
      int * Crrtab = upsample->Cr_r_tab;
      int * Cbbtab = upsample->Cb_b_tab;
      INT32 * Crgtab = upsample->Cr_g_tab;
      INT32 * Cbgtab = upsample->Cb_g_tab;
      SHIFT_TEMPS

      inptr0 = input_buf[0][in_row_group_ctr];
      inptr1 = input_buf[1][in_row_group_ctr];
      inptr2 = input_buf[2][in_row_group_ctr];
      outptr = output_buf[0];
      /* Loop for each pair of output pixels */
      for (col = cinfo->output_width >> 1; col > 0; col--) {
        /* Do the chroma part of the calculation */
        cb = GETJSAMPLE(*inptr1++);
        cr = GETJSAMPLE(*inptr2++);
        cred   = Crrtab[cr];
        cgreen = (int) RIGHT_SHIFT(Cbgtab[cb] + Crgtab[cr], SCALEBITS);
        cblue  = Cbbtab[cb];
        /* Fetch 2 Y values and emit 2 pixels */
        y  = GETJSAMPLE(*inptr0++);
        outptr[RGB_RED]   = range_limit[y + cred];
        outptr[RGB_GREEN] = range_limit[y + cgreen];
        outptr[RGB_BLUE]  = range_limit[y + cblue];
        outptr += RGB_PIXELSIZE;
        y  = GETJSAMPLE(*inptr0++);
        outptr[RGB_RED]   = range_limit[y + cred];
        outptr[RGB_GREEN] = range_limit[y + cgreen];
        outptr[RGB_BLUE]  = range_limit[y + cblue];
        outptr += RGB_PIXELSIZE;
      }
      /* If image width is odd, do the last output column separately */
      if (cinfo->output_width & 1) {
        cb = GETJSAMPLE(*inptr1);
        cr = GETJSAMPLE(*inptr2);
        cred   = Crrtab[cr];
        cgreen = (int) RIGHT_SHIFT(Cbgtab[cb] + Crgtab[cr], SCALEBITS);
        cblue  = Cbbtab[cb];
        y  = GETJSAMPLE(*inptr0);
        outptr[RGB_RED]   = range_limit[y + cred];
        outptr[RGB_GREEN] = range_limit[y + cgreen];
        outptr[RGB_BLUE]  = range_limit[y + cblue];
      }
    }

    /*
     * Upsample and color convert for the case of 2:1 horizontal and 2:1 vertical.
     */

    METHODDEF(void)
    h2v2_merged_upsample (j_decompress_ptr cinfo,
    		      JSAMPIMAGE input_buf, JDIMENSION in_row_group_ctr,
    		      JSAMPARRAY output_buf)
    {
      my_upsample_ptr upsample = (my_upsample_ptr) cinfo->upsample;
      register int y, cred, cgreen, cblue;
      int cb, cr;
      register JSAMPROW outptr0, outptr1;
      JSAMPROW inptr00, inptr01, inptr1, inptr2;
      JDIMENSION col;
      /* copy these pointers into registers if possible */
      register JSAMPLE * range_limit = cinfo->sample_range_limit;
      int * Crrtab = upsample->Cr_r_tab;
      int * Cbbtab = upsample->Cb_b_tab;
      INT32 * Crgtab = upsample->Cr_g_tab;
      INT32 * Cbgtab = upsample->Cb_g_tab;
      SHIFT_TEMPS

      inptr00 = input_buf[0][in_row_group_ctr*2];
      inptr01 = input_buf[0][in_row_group_ctr*2 + 1];
      inptr1 = input_buf[1][in_row_group_ctr];
      inptr2 = input_buf[2][in_row_group_ctr];
      outptr0 = output_buf[0];
      outptr1 = output_buf[1];
      /* Loop for each group of output pixels */
      for (col = cinfo->output_width >> 1; col > 0; col--) {
        /* Do the chroma part of the calculation */
        cb = GETJSAMPLE(*inptr1++);
        cr = GETJSAMPLE(*inptr2++);
        cred   = Crrtab[cr];
        cgreen = (int) RIGHT_SHIFT(Cbgtab[cb] + Crgtab[cr], SCALEBITS);
        cblue  = Cbbtab[cb];
        /* Fetch 4 Y values and emit 4 pixels */
        y  = GETJSAMPLE(*inptr00++);
        outptr0[RGB_RED]   = range_limit[y + cred];
        outptr0[RGB_GREEN] = range_limit[y + cgreen];
        outptr0[RGB_BLUE]  = range_limit[y + cblue];
        outptr0 += RGB_PIXELSIZE;
        y  = GETJSAMPLE(*inptr00++);
        outptr0[RGB_RED]   = range_limit[y + cred];
        outptr0[RGB_GREEN] = range_limit[y + cgreen];
        outptr0[RGB_BLUE]  = range_limit[y + cblue];
        outptr0 += RGB_PIXELSIZE;
        y  = GETJSAMPLE(*inptr01++);
        outptr1[RGB_RED]   = range_limit[y + cred];
        outptr1[RGB_GREEN] = range_limit[y + cgreen];
        outptr1[RGB_BLUE]  = range_limit[y + cblue];
        outptr1 += RGB_PIXELSIZE;
        y  = GETJSAMPLE(*inptr01++);
        outptr1[RGB_RED]   = range_limit[y + cred];
        outptr1[RGB_GREEN] = range_limit[y + cgreen];
        outptr1[RGB_BLUE]  = range_limit[y + cblue];
        outptr1 += RGB_PIXELSIZE;
      }
      /* If image width is odd, do the last output column separately */
      if (cinfo->output_width & 1) {
        cb = GETJSAMPLE(*inptr1);
        cr = GETJSAMPLE(*inptr2);
        cred   = Crrtab[cr];
        cgreen = (int) RIGHT_SHIFT(Cbgtab[cb] + Crgtab[cr], SCALEBITS);
        cblue  = Cbbtab[cb];
        y  = GETJSAMPLE(*inptr00);
        outptr0[RGB_RED]   = range_limit[y + cred];
        outptr0[RGB_GREEN] = range_limit[y + cgreen];
        outptr0[RGB_BLUE]  = range_limit[y + cblue];
        y  = GETJSAMPLE(*inptr01);
        outptr1[RGB_RED]   = range_limit[y + cred];
        outptr1[RGB_GREEN] = range_limit[y + cgreen];
        outptr1[RGB_BLUE]  = range_limit[y + cblue];
      }
    }

    /*
     * Module initialization routine for merged upsampling/color conversion.
     *
     * NB: this is called under the conditions determined by use_merged_upsample()
     * in jdmaster.c.  That routine MUST correspond to the actual capabilities
     * of this module; no safety checks are made here.
     */

    GLOBAL(void)
    jinit_merged_upsampler (j_decompress_ptr cinfo)
    {
      my_upsample_ptr upsample;

      upsample = (my_upsample_ptr) (*cinfo->mem->alloc_small)
        ((j_common_ptr) cinfo, JPOOL_IMAGE, SIZEOF(my_upsampler));
      cinfo->upsample = &upsample->pub;
      upsample->pub.start_pass = start_pass_merged_upsample;
      upsample->pub.need_context_rows = FALSE;

      upsample->out_row_width = cinfo->output_width * cinfo->out_color_components;

      if (cinfo->max_v_samp_factor == 2) {
        upsample->pub.upsample = merged_2v_upsample;
        upsample->upmethod = h2v2_merged_upsample;
        /* Allocate a spare row buffer */
        upsample->spare_row = (JSAMPROW) (*cinfo->mem->alloc_large)
          ((j_common_ptr) cinfo, JPOOL_IMAGE,
           (size_t) upsample->out_row_width * SIZEOF(JSAMPLE));
      } else {
        upsample->pub.upsample = merged_1v_upsample;
        upsample->upmethod = h2v1_merged_upsample;
        /* No spare row needed */
        upsample->spare_row = NULL;
      }

      if (cinfo->jpeg_color_space == JCS_BG_YCC)
        build_bg_ycc_rgb_table(cinfo);
      else
        build_ycc_rgb_table(cinfo);
    }

    #endif /* UPSAMPLE_MERGING_SUPPORTED */