#include <u.h>
#include <libc.h>
#include <draw.h>
#include "dat.h"
#include "fns.h"

enum
{
	Bits5	= 0x1F,
	Bits7 = 0x7F,
};

static uchar*
gbuint7(uchar *p, uchar* ep, int* pv)
{
	uint u,v,go;

	v = 0;
	go = 1;
	while(go){
		if(p >= ep){
			werrstr(Eshort);
			return nil;
		}
		u = *p;
		v = (v<<7) | (u&Bits7);
		if(v&(Bits7<<24)){
			werrstr(Ebignum);
			return nil;
		}
		go = u&(1<<7);
		p++;
	}
	*pv = v;
	return p;	
}

uchar*
gbtag(uchar *p, uchar* ep, int* ptag)
{
	if(p >= ep){
		werrstr(Eshort);
		return nil;
	}
	*ptag = p[0] & Bits5;
	p += 1;
	if(*ptag == Bits5)
		p = gbuint7(p, ep, ptag);
	return p;
}

uchar*
gblen(uchar *p, uchar* ep, int* plen)
{
	int c,v;

	if(p >= ep){
		werrstr(Eshort);
		return nil;
	}

	v = *p++;
	if(v < (1<<7)){
		*plen = v;
		return p;
	}
	c = v&Bits7;
	if(p+c >= ep){
		werrstr(Eshort);
		return nil;
	}
	switch(c){
	default:
		werrstr(Ebignum);
		return nil;
	case 0:
		*plen = 0;
		break;
	case 1:
		*plen = p[0];
		break;
	case 2:
		*plen = GSHORTB(p);
		break;
	case 3:
		*plen = (GSHORTB(p)<<8)|p[2];
		break;
	case 4:
		*plen = GLONGB(p);
		break;
	}
	return p+c;
}

void
pbshort(uchar* p, int v)
{
	p[0]=2;
	p[1]=2;
	PSHORTB(p+2,v);
}