csc.c

这是一个SIGMA方案的PMP播放器的UCLINUX程序,可播放DVD,VCD,CD MP3...有很好的参考价值.

/*****************************************************************
*** Copyright (c) 2002 Sigma Designs Inc. All rights reserved. ***
*****************************************************************/

/*
  @file   csc.c
  See licensing details in LICENSING file  
*/

#include "common.h"

#define START 0
#define END 65536
#define PRECISION 20

// u=0; while [ $u -lt 21 ]; do echo $u; u=$[$u+1]; done |awk '{printf("%d,\n",65536*($1/20)^2.2);}'
static unsigned long powertwodottwotable[PRECISION+1]={
0,
89,
413,
1008,
1899,
3104,
4636,
6507,
8729,
11312,
14263,
17590,
21301,
25403,
29901,
34802,
40112,
45835,
51977,
58542,
65536
};

static unsigned long invertofpowertwodottwotable[PRECISION+1]={
0,
16792,
23010,
27667,
31533,
34899,
37914,
40666,
43211,
45587,
47824,
49941,
51956,
53881,
55727,
57502,
59214,
60869,
62471,
64025,
65536
};

// computes y/65536=f(x/65536) with 0<=x,y<65536 with f=^2.2 or ^(1/2.2) given as a unsigned long table (have to code the 65536 case)
static unsigned short compute_f(unsigned long beg,unsigned long end,unsigned long prec,unsigned long *table,unsigned short x)
{
	long a,b,fa,fb,entry;
	
	if (beg==end) {
		printk("memory corrupted beg=%ld end=%ld\n",beg,end);
		return;
	}
	entry=(x-beg)*prec/(end-beg);

	if ((entry<0)||(entry>=20)) {
		printk("memory corrupted x=%hd beg=%ld end=%ld prec=%ld\n",x,beg,end,prec);
		return;
	}

	a=entry*(end-beg)/prec+beg;
	b=(entry+1)*(end-beg)/prec+beg;
	fa=table[entry];
	fb=table[entry+1];
	return (unsigned short)(fa+(fb-fa)*(x-a)/(b-a));
}

// see video demystified page 43
static void gammacorrectedrgbtoyuv(unsigned short R,unsigned short G,unsigned short B,unsigned short *y,unsigned short *u,unsigned short *v)
{
	long yraw,uraw,vraw;
	
	yraw=( 257*R  +504*G + 98*B)/1000 + RANGE8TO16(16);
	uraw=(-148*R  -291*G +439*B)/1000 + RANGE8TO16(128);
	vraw=( 439*R  -368*G - 71*B)/1000 + RANGE8TO16(128);

	/* Obviously the computation of yraw garantees >= RANGE8TO16(16) ;-)
	   This is also true for uraw and vraw */
	
	*y=MAX(MIN(yraw,RANGE8TO16(235)),RANGE8TO16(16)); 
	*u=MAX(MIN(uraw,RANGE8TO16(240)),RANGE8TO16(16));
	*v=MAX(MIN(vraw,RANGE8TO16(240)),RANGE8TO16(16));
}

static void yuvtorgbgammacorrected(unsigned short y,unsigned short u,unsigned short v,unsigned short *R,unsigned short *G,unsigned short *B)
{
	long Rraw,Graw,Braw;
	long ym=y-RANGE8TO16(16),um=u-RANGE8TO16(128),vm=v-RANGE8TO16(128);

	Rraw=(1164*ym        +1596*vm)/1000;
	Graw=(1164*ym+ 392*um- 813*vm)/1000;
	Braw=(1164*ym+2017*um        )/1000;

	*R=MAX(0,MIN(Rraw,RANGE8TO16(255)));
	*G=MAX(0,MIN(Graw,RANGE8TO16(255)));
	*B=MAX(0,MIN(Braw,RANGE8TO16(255)));
}

void vgargbtotvyuv(unsigned short R,unsigned short G,unsigned short B,unsigned short *y,unsigned short *u,unsigned short *v)
{
	unsigned short Rc,Gc,Bc;

	Rc=compute_f(START,END,PRECISION,powertwodottwotable,R);
	Gc=compute_f(START,END,PRECISION,powertwodottwotable,G);
	Bc=compute_f(START,END,PRECISION,powertwodottwotable,B);
	gammacorrectedrgbtoyuv(Rc,Gc,Bc,y,u,v);
}

void tvyuvtovgargb(unsigned short y,unsigned short u,unsigned short v,unsigned short *R,unsigned short *G,unsigned short *B)
{
	unsigned short Ruc,Guc,Buc;

	yuvtorgbgammacorrected(y,u,v,&Ruc,&Guc,&Buc);
	*R=compute_f(START,END,PRECISION,invertofpowertwodottwotable,Ruc);
	*G=compute_f(START,END,PRECISION,invertofpowertwodottwotable,Guc);
	*B=compute_f(START,END,PRECISION,invertofpowertwodottwotable,Buc);
}