#include <u.h>
#include <libc.h>
#include <libg.h>
#include <fb.h>
#define	NBIT	8		/* bits per uchar, a source of non-portability */
Bitmap *rdpicfile(PICFILE *f, int ldepth){
	int wid=PIC_WIDTH(f);
	int hgt=PIC_HEIGHT(f);
	int nchan=PIC_NCHAN(f);
	int w=1<<ldepth;
	int nval=1<<w;
	int i;
	uchar lummap[1<<NBIT];
	Bitmap *b=balloc(Rect(0, 0, wid, hgt), ldepth);
	char *buf=malloc(wid*nchan);
	uchar *data=malloc((wid*w+NBIT-1)/NBIT);
	int *error=malloc((wid+2)*sizeof(int));
	int *ep, *eerror, cerror, y, lum, value, shift, pv;
	uchar *dp;
	char *p;
	if(buf==0 || error==0 || data==0 || b==0){
		if(buf) free(buf);
		if(error) free(error);
		if(data) free(data);
		if(b) bfree(b);
		return 0;
	}
	eerror=error+wid+1;
	switch(nchan){
	case 3:
	case 4:
	case 7:
	case 8:
		lum=1;
		break;
	default:
		lum=0;
	}
	if(f->cmap){
		for(i=0,p=f->cmap;i!=1<<NBIT;i++,p+=3)
			lummap[i]=((p[0]&255)*299+(p[1]&255)*587+(p[2]&255)*114)/1000;
	}
	else{
		for(i=0;i!=1<<NBIT;i++) lummap[i]=i;
	}
	for(ep=error;ep<=eerror;ep++) *ep=0;
	for(y=0;y!=hgt;y++){
		cerror=0;
		picread(f, buf);
		p=buf;
		dp=data-1;
		shift=0;
		for(ep=error+1;ep!=eerror;ep++){
			shift-=w;
			if(shift<0){
				shift+=NBIT;
				*++dp=0;
			}
			if(lum)
				value=((p[0]&255)*299+(p[1]&255)*587+(p[2]&255)*114)/1000;
			else
				value=lummap[p[0]&255];
			value+=ep[0]/16;
			pv=value<=0?0:value<255?value*nval/256:nval-1;
			p+=nchan;
			*dp|=(nval-1-pv)<<shift;
			value-=pv*255/(nval-1);
			ep[1]+=value*7;
			ep[-1]+=value*3;
			ep[0]=cerror+value*5;
			cerror=value;
		}
		wrbitmap(b, y, y+1, data);
	}
	free(buf);
	free(error);
	free(data);
	return b;
}