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colrops.c
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1992-06-16
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/* Copyright (c) 1990 Regents of the University of California */
#ifndef lint
static char SCCSid[] = "@(#)colrops.c 1.3 11/9/90 LBL";
#endif
/*
* Integer operations on COLR scanlines
*/
#include "color.h"
#define MAXGSHIFT 15 /* maximum shift for gamma table */
static BYTE g_mant[256], g_nexp[256];
static BYTE g_bval[MAXGSHIFT+1][256];
setcolrgam(g) /* set gamma conversion */
double g;
{
extern double pow();
double mult;
register int i, j;
/* compute colr -> gamb mapping */
for (i = 0; i <= MAXGSHIFT; i++) {
mult = pow(0.5, (double)(i+8));
for (j = 0; j < 256; j++)
g_bval[i][j] = 256.0 * pow((j+.5)*mult, 1.0/g);
}
/* compute gamb -> colr mapping */
i = 0;
mult = 256.0;
for (j = 255; j > 0; j--) {
while ((g_mant[j] = mult * pow(j/256.0, g)) < 128) {
i++;
mult *= 2.0;
}
g_nexp[j] = i;
}
g_mant[0] = 0;
g_nexp[0] = COLXS;
}
colrs_gambs(scan, len) /* convert scanline of colrs to gamma bytes */
register COLR *scan;
int len;
{
register int i, expo;
while (len-- > 0) {
expo = scan[0][EXP] - COLXS;
if (expo < -MAXGSHIFT) {
if (expo < -MAXGSHIFT-8) {
scan[0][RED] =
scan[0][GRN] =
scan[0][BLU] = 0;
} else {
i = (-MAXGSHIFT-1) - expo;
scan[0][RED] =
g_bval[MAXGSHIFT][((scan[0][RED]>>i)+1)>>1];
scan[0][GRN] =
g_bval[MAXGSHIFT][((scan[0][GRN]>>i)+1)>>1];
scan[0][BLU] =
g_bval[MAXGSHIFT][((scan[0][BLU]>>i)+1)>>1];
}
} else if (expo > 0) {
if (expo > 8) {
scan[0][RED] =
scan[0][GRN] =
scan[0][BLU] = 255;
} else {
i = (scan[0][RED]<<1 | 1) << (expo-1);
scan[0][RED] = i > 255 ? 255 : g_bval[0][i];
i = (scan[0][GRN]<<1 | 1) << (expo-1);
scan[0][GRN] = i > 255 ? 255 : g_bval[0][i];
i = (scan[0][BLU]<<1 | 1) << (expo-1);
scan[0][BLU] = i > 255 ? 255 : g_bval[0][i];
}
} else {
scan[0][RED] = g_bval[-expo][scan[0][RED]];
scan[0][GRN] = g_bval[-expo][scan[0][GRN]];
scan[0][BLU] = g_bval[-expo][scan[0][BLU]];
}
scan[0][EXP] = COLXS;
scan++;
}
}
gambs_colrs(scan, len) /* convert gamma bytes to colr scanline */
register COLR *scan;
int len;
{
register int nexpo;
while (len-- > 0) {
nexpo = g_nexp[scan[0][RED]];
if (g_nexp[scan[0][GRN]] < nexpo)
nexpo = g_nexp[scan[0][GRN]];
if (g_nexp[scan[0][BLU]] < nexpo)
nexpo = g_nexp[scan[0][BLU]];
if (nexpo < g_nexp[scan[0][RED]])
scan[0][RED] = g_mant[scan[0][RED]]
>> (g_nexp[scan[0][RED]]-nexpo);
else
scan[0][RED] = g_mant[scan[0][RED]];
if (nexpo < g_nexp[scan[0][GRN]])
scan[0][GRN] = g_mant[scan[0][GRN]]
>> (g_nexp[scan[0][GRN]]-nexpo);
else
scan[0][GRN] = g_mant[scan[0][GRN]];
if (nexpo < g_nexp[scan[0][BLU]])
scan[0][BLU] = g_mant[scan[0][BLU]]
>> (g_nexp[scan[0][BLU]]-nexpo);
else
scan[0][BLU] = g_mant[scan[0][BLU]];
scan[0][EXP] = COLXS - nexpo;
scan++;
}
}
shiftcolrs(scan, len, adjust) /* shift a scanline of colors by 2^adjust */
register COLR *scan;
register int len;
register int adjust;
{
while (len-- > 0) {
scan[0][EXP] += adjust;
scan++;
}
}
normcolrs(scan, len, adjust) /* normalize a scanline of colrs */
register COLR *scan;
int len;
int adjust;
{
register int c;
register int shift;
while (len-- > 0) {
shift = scan[0][EXP] + adjust - COLXS;
if (shift > 0) {
if (shift > 8) {
scan[0][RED] =
scan[0][GRN] =
scan[0][BLU] = 255;
} else {
shift--;
c = (scan[0][RED]<<1 | 1) << shift;
scan[0][RED] = c > 255 ? 255 : c;
c = (scan[0][GRN]<<1 | 1) << shift;
scan[0][GRN] = c > 255 ? 255 : c;
c = (scan[0][BLU]<<1 | 1) << shift;
scan[0][BLU] = c > 255 ? 255 : c;
}
} else if (shift < 0) {
if (shift < -8) {
scan[0][RED] =
scan[0][GRN] =
scan[0][BLU] = 0;
} else {
shift = -1-shift;
scan[0][RED] = ((scan[0][RED]>>shift)+1)>>1;
scan[0][GRN] = ((scan[0][GRN]>>shift)+1)>>1;
scan[0][BLU] = ((scan[0][BLU]>>shift)+1)>>1;
}
}
scan[0][EXP] = COLXS - adjust;
scan++;
}
}