/* Copyright (c) 1992 AT&T - All rights reserved. */
#include	<u.h>
#include	<string.h>
#include	<libc.h>

enum
{
	Bit1	= 7,
	Bitx	= 6,
	Bit2	= 5,
	Bit3	= 4,
	Bit4	= 3,

	T1	= ((1<<(Bit1+1))-1) ^ 0xFF,	/* 0000 0000 */
	Tx	= ((1<<(Bitx+1))-1) ^ 0xFF,	/* 1000 0000 */
	T2	= ((1<<(Bit2+1))-1) ^ 0xFF,	/* 1100 0000 */
	T3	= ((1<<(Bit3+1))-1) ^ 0xFF,	/* 1110 0000 */
	T4	= ((1<<(Bit4+1))-1) ^ 0xFF,	/* 1111 0000 */

	Rune1	= (1<<(Bit1+0*Bitx))-1,		/* 0000 0000 0111 1111 */
	Rune2	= (1<<(Bit2+1*Bitx))-1,		/* 0000 0111 1111 1111 */
	Rune3	= (1<<(Bit3+2*Bitx))-1,		/* 1111 1111 1111 1111 */

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

	Bad	= Runeerror
};

int
chartorune(Rune *rune, char *str)
{
	int c, c1, c2;
	long l;

	/*
	 * one character sequence
	 *	00000-0007F => T1
	 */
	c = *(uchar*)str;
	if(c < Tx) {
		*rune = c;
		return 1;
	}

	/*
	 * two character sequence
	 *	0080-07FF => T2 Tx
	 */
	c1 = *(uchar*)(str+1) ^ Tx;
	if(c1 & Testx)
		goto bad;
	if(c < T3) {
		if(c < T2)
			goto bad;
		l = ((c << Bitx) | c1) & Rune2;
		if(l <= Rune1)
			goto bad;
		*rune = l;
		return 2;
	}

	/*
	 * three character sequence
	 *	0800-FFFF => T3 Tx Tx
	 */
	c2 = *(uchar*)(str+2) ^ Tx;
	if(c2 & Testx)
		goto bad;
	if(c < T4) {
		l = ((((c << Bitx) | c1) << Bitx) | c2) & Rune3;
		if(l <= Rune2)
			goto bad;
		*rune = l;
		return 3;
	}

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

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

	/*
	 * one character sequence
	 *	00000-0007F => 00-7F
	 */
	c = *rune;
	if(c <= Rune1) {
		str[0] = c;
		return 1;
	}

	/*
	 * two character sequence
	 *	0080-07FF => T2 Tx
	 */
	if(c <= Rune2) {
		str[0] = T2 | (c >> 1*Bitx);
		str[1] = Tx | (c & Maskx);
		return 2;
	}

	/*
	 * three character sequence
	 *	0800-FFFF => T3 Tx Tx
	 */
	str[0] = T3 |  (c >> 2*Bitx);
	str[1] = Tx | ((c >> 1*Bitx) & Maskx);
	str[2] = Tx |  (c & Maskx);
	return 3;
}

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

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

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

	if(n > 0) {
		c = *(uchar*)str;
		if(c < Tx)
			return 1;
		if(n > 1)
			if(c < T3 || n > 2)
				return 1;
	}
	return 0;
}

char*
utfrune(char *s, long c)
{
	long c1;
	Rune r;
	int n;

	if(c < Runesync)		/* not part of utf sequence */
		return strchr(s, c);

	for(;;) {
		c1 = *(uchar*)s;
		if(c1 < Runeself) {	/* one byte rune */
			if(c1 == 0)
				return 0;
			if(c1 == c)
				return s;
			s++;
			continue;
		}
		n = chartorune(&r, s);
		if(r == c)
			return s;
		s += n;
	}
	return 0;
}

long
utflen(char *s)
{
	int c;
	long n;
	Rune rune;

	n = 0;
	for(;;) {
		c = *(uchar*)s;
		if(c < Runeself) {
			if(c == 0)
				return n;
			s++;
		} else
			s += chartorune(&rune, s);
		n++;
	}
	return 0;
}
