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  Everyone is granted permission to copy, modify and redistribute GNU
  Ghostscript, but only under the conditions described in the GNU General
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*/

/*$RCSfile: gxctable.c,v $ $Revision: 1.3.2.1 $ */
/* Color table lookup and interpolation */
#include "gx.h"
#include "gxfixed.h"
#include "gxfrac.h"
#include "gxctable.h"

/* See gxctable.h for the API and structure definitions. */

/*
 * Define an implementation that simply picks the nearest value without
 * any interpolation.
 */
void
gx_color_interpolate_nearest(const fixed * pi,
			     const gx_color_lookup_table * pclt, frac * pv)
{
    const int *pdim = pclt->dims;
    int m = pclt->m;
    const gs_const_string *table = pclt->table;

    if (pclt->n > 3) {
	table += fixed2int_var_rounded(pi[0]) * pdim[1];
	++pi, ++pdim;
    } {
	int ic = fixed2int_var_rounded(pi[2]);
	int ib = fixed2int_var_rounded(pi[1]);
	int ia = fixed2int_var_rounded(pi[0]);
	const byte *p = pclt->table[ia].data + (ib * pdim[2] + ic) * m;
	int j;

	for (j = 0; j < m; ++j, ++p)
	    pv[j] = byte2frac(*p);
    }
}

/*
 * Define an implementation that uses trilinear interpolation.
 */
private void
interpolate_accum(const fixed * pi, const gx_color_lookup_table * pclt,
		  frac * pv, fixed factor)
{
    const int *pdim = pclt->dims;
    int m = pclt->m;

    if (pclt->n > 3) {
	/* Do two 3-D interpolations, interpolating between them. */
	gx_color_lookup_table clt3;
	int ix = fixed2int_var(pi[0]);
	fixed fx = fixed_fraction(pi[0]);

	clt3.n = 3;
	clt3.dims[0] = pdim[1];	/* needed only for range checking */
	clt3.dims[1] = pdim[2];
	clt3.dims[2] = pdim[3];
	clt3.m = m;
	clt3.table = pclt->table + ix * pdim[1];
	interpolate_accum(pi + 1, &clt3, pv, fixed_1);
	if (ix == pdim[0] - 1)
	    return;
	clt3.table += pdim[1];
	interpolate_accum(pi + 1, &clt3, pv, fx);
    } else {
	int ic = fixed2int_var(pi[2]);
	fixed fc = fixed_fraction(pi[2]);
	uint dc1 = (ic == pdim[2] - 1 ? 0 : m);
	int ib = fixed2int_var(pi[1]);
	fixed fb = fixed_fraction(pi[1]);
	uint db1 = (ib == pdim[1] - 1 ? 0 : pdim[2] * m);
	uint dbc = (ib * pdim[2] + ic) * m;
	uint dbc1 = db1 + dc1;
	int ia = fixed2int_var(pi[0]);
	fixed fa = fixed_fraction(pi[0]);
	const byte *pa0 = pclt->table[ia].data + dbc;
	const byte *pa1 =
	    (ia == pdim[0] - 1 ? pa0 : pclt->table[ia + 1].data + dbc);
	int j;

	/* The values to be interpolated are */
	/* pa{0,1}[{0,db1,dc1,dbc1}]. */
	for (j = 0; j < m; ++j, ++pa0, ++pa1) {
	    frac v000 = byte2frac(pa0[0]);
	    frac v001 = byte2frac(pa0[dc1]);
	    frac v010 = byte2frac(pa0[db1]);
	    frac v011 = byte2frac(pa0[dbc1]);
	    frac v100 = byte2frac(pa1[0]);
	    frac v101 = byte2frac(pa1[dc1]);
	    frac v110 = byte2frac(pa1[db1]);
	    frac v111 = byte2frac(pa1[dbc1]);
	    frac rv;

	    frac v00 = v000 +
		(frac) arith_rshift((long)fc * (v001 - v000),
				    _fixed_shift);
	    frac v01 = v010 +
		(frac) arith_rshift((long)fc * (v011 - v010),
				    _fixed_shift);
	    frac v10 = v100 +
		(frac) arith_rshift((long)fc * (v101 - v100),
				    _fixed_shift);
	    frac v11 = v110 +
		(frac) arith_rshift((long)fc * (v111 - v110),
				    _fixed_shift);

	    frac v0 = v00 +
		(frac) arith_rshift((long)fb * (v01 - v00),
				    _fixed_shift);
	    frac v1 = v10 +
		(frac) arith_rshift((long)fb * (v11 - v10),
				    _fixed_shift);

	    rv = v0 +
		(frac) arith_rshift((long)fa * (v1 - v0),
				    _fixed_shift);
	    if (factor == fixed_1)
		pv[j] = rv;
	    else
		pv[j] += (frac) arith_rshift((long)factor * (rv - pv[j]),
					     _fixed_shift);
	}
    }
}
void
gx_color_interpolate_linear(const fixed * pi,
			    const gx_color_lookup_table * pclt, frac * pv)
{
    interpolate_accum(pi, pclt, pv, fixed_1);
}
