#include	<u.h>
#include	<libc.h>

#define Bit(i) (7-(i))
/* N 0's preceded by i 1's, T(Bit(2)) is 1100 0000 */
#define T(i) (((1 << (Bit(i)+1))-1) ^ 0xFF)
/* 0000 0000 0000 0111 1111 1111 */
#define	RuneX(i) ((1 << (Bit(i) + ((i)-1)*Bitx))-1)

enum
{
	Bitx	= Bit(1),

	Tx	= T(1),			/* 1000 0000 */
	Rune1 = (1<<(Bit(0)+0*Bitx))-1,	/* 0000 0000 0000 0000 0111 1111 */

	Maskx	= (1<<Bitx)-1,		/* 0011 1111 */
	Testx	= Maskx ^ 0xFF,		/* 1100 0000 */

	SurrogateMin	= 0xD800,
	SurrogateMax	= 0xDFFF,

	Bad	= Runeerror,
};

int
chartorune(Rune *rune, char *str)
{
	int c[UTFmax], i;
	Rune l;

	/*
	 * N character sequence
	 *	00000-0007F => T1
	 *	00080-007FF => T2 Tx
	 *	00800-0FFFF => T3 Tx Tx
	 *	10000-10FFFF => T4 Tx Tx Tx
	 */

	c[0] = *(uchar*)(str);
	if(c[0] < Tx){
		*rune = c[0];
		return 1;
	}
	l = c[0];

	for(i = 1; i < UTFmax; i++) {
		c[i] = *(uchar*)(str+i);
		c[i] ^= Tx;
		if(c[i] & Testx)
			goto bad;
		l = (l << Bitx) | c[i];
		if(c[0] < T(i + 2)) {
			l &= RuneX(i + 1);
			if(i == 1) {
				if(c[0] < T(2) || l <= Rune1)
					goto bad;
			} else if(l <= RuneX(i) || l > Runemax)
				goto bad;
			if (i == 2 && SurrogateMin <= l && l <= SurrogateMax)
				goto bad;
			*rune = l;
			return i + 1;
		}
	}

	/*
	 * bad decoding
	 */
bad:
	*rune = Bad;
	return 1;
}

int
runetochar(char *str, Rune *rune)
{
	int i, j;
	Rune c;

	c = *rune;
	if(c <= Rune1) {
		str[0] = c;
		return 1;
	}

	/*
	 * one character sequence
	 *	00000-0007F => 00-7F
	 * two character sequence
	 *	0080-07FF => T2 Tx
	 * three character sequence
	 *	0800-FFFF => T3 Tx Tx
	 * four character sequence (21-bit value)
	 *     10000-1FFFFF => T4 Tx Tx Tx
	 * If the Rune is out of range or a surrogate half,
	 * convert it to the error rune.
	 * Do this test when i==3 because the error rune encodes to three bytes.
	 * Doing it earlier would duplicate work, since an out of range
	 * Rune wouldn't have fit in one or two bytes.
	 */
	for(i = 2; i < UTFmax + 1; i++){
		if(i == 3){
			if(c > Runemax)
				c = Runeerror;
			if(SurrogateMin <= c && c <= SurrogateMax)
				c = Runeerror;
		}
		if (c <= RuneX(i) || i == UTFmax ) {
			str[0] = T(i) |  (c >> (i - 1)*Bitx);
			for(j = 1; j < i; j++)
				str[j] = Tx | ((c >> (i - j - 1)*Bitx) & Maskx);
			return i;
		}
	}
	return UTFmax;
}

int
runelen(long c)
{
	Rune rune;
	char str[10];

	rune = c;
	return runetochar(str, &rune);
}

int
runenlen(Rune *r, int nrune)
{
	int nb, i;
	Rune c;

	nb = 0;
	while(nrune--) {
		c = *r++;
		if(c <= Rune1){
			nb++;
		} else {
			for(i = 2; i < UTFmax + 1; i++)
				if(c <= RuneX(i) || i == UTFmax){
					nb += i;
					break;
				}
		}
	}
	return nb;
}

int
fullrune(char *str, int n)
{
	int  i;
	Rune c;

	if(n <= 0)
		return 0;
	c = *(uchar*)str;
	if(c < Tx)
		return 1;
	for(i = 3; i < UTFmax + 1; i++)
		if(c < T(i))
			return n >= i - 1;
	return n >= UTFmax;
}