github.com/tcnksm/go@v0.0.0-20141208075154-439b32936367/src/lib9/utf/rune.c

/*
 * The authors of this software are Rob Pike and Ken Thompson.
 *              Copyright (c) 2002 by Lucent Technologies.
 *              Portions Copyright (c) 2009 The Go Authors.  All rights reserved.
 * Permission to use, copy, modify, and distribute this software for any
 * purpose without fee is hereby granted, provided that this entire notice
 * is included in all copies of any software which is or includes a copy
 * or modification of this software and in all copies of the supporting
 * documentation for such software.
 * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
 * WARRANTY.  IN PARTICULAR, NEITHER THE AUTHORS NOR LUCENT TECHNOLOGIES MAKE ANY
 * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
 * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
 */
#include "utf.h"
#include "utfdef.h"

enum
{
	Bit1	= 7,
	Bitx	= 6,
	Bit2	= 5,
	Bit3	= 4,
	Bit4	= 3,
	Bit5	= 2,

	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 */
	T5	= ((1<<(Bit5+1))-1) ^ 0xFF,	/* 1111 1000 */

	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 */
	Rune4	= (1<<(Bit4+3*Bitx))-1,		/* 0001 1111 1111 1111 1111 1111 */

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

	SurrogateMin	= 0xD800,
	SurrogateMax	= 0xDFFF,

	Bad	= Runeerror,
};

/*
 * Modified by Wei-Hwa Huang, Google Inc., on 2004-09-24
 * This is a slower but "safe" version of the old chartorune
 * that works on strings that are not necessarily null-terminated.
 *
 * If you know for sure that your string is null-terminated,
 * chartorune will be a bit faster.
 *
 * It is guaranteed not to attempt to access "length"
 * past the incoming pointer.  This is to avoid
 * possible access violations.  If the string appears to be
 * well-formed but incomplete (i.e., to get the whole Rune
 * we'd need to read past str+length) then we'll set the Rune
 * to Bad and return 0.
 *
 * Note that if we have decoding problems for other
 * reasons, we return 1 instead of 0.
 */
int
charntorune(Rune *rune, const char *str, int length)
{
	int c, c1, c2, c3;
	long l;

	/* When we're not allowed to read anything */
	if(length <= 0) {
		goto badlen;
	}

	/*
	 * one character sequence (7-bit value)
	 *	00000-0007F => T1
	 */
	c = *(uchar*)str;
	if(c < Tx) {
		*rune = (Rune)c;
		return 1;
	}

	// If we can't read more than one character we must stop
	if(length <= 1) {
		goto badlen;
	}

	/*
	 * two character sequence (11-bit value)
	 *	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 = (Rune)l;
		return 2;
	}

	// If we can't read more than two characters we must stop
	if(length <= 2) {
		goto badlen;
	}

	/*
	 * three character sequence (16-bit value)
	 *	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;
		if (SurrogateMin <= l && l <= SurrogateMax)
			goto bad;
		*rune = (Rune)l;
		return 3;
	}

	if (length <= 3)
		goto badlen;

	/*
	 * four character sequence (21-bit value)
	 *	10000-1FFFFF => T4 Tx Tx Tx
	 */
	c3 = *(uchar*)(str+3) ^ Tx;
	if (c3 & Testx)
		goto bad;
	if (c < T5) {
		l = ((((((c << Bitx) | c1) << Bitx) | c2) << Bitx) | c3) & Rune4;
		if (l <= Rune3 || l > Runemax)
			goto bad;
		*rune = (Rune)l;
		return 4;
	}

	// Support for 5-byte or longer UTF-8 would go here, but
	// since we don't have that, we'll just fall through to bad.

	/*
	 * bad decoding
	 */
bad:
	*rune = Bad;
	return 1;
badlen:
	*rune = Bad;
	return 0;

}


/*
 * This is the older "unsafe" version, which works fine on
 * null-terminated strings.
 */
int
chartorune(Rune *rune, const char *str)
{
	int c, c1, c2, c3;
	long l;

	/*
	 * one character sequence
	 *	00000-0007F => T1
	 */
	c = *(uchar*)str;
	if(c < Tx) {
		*rune = (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 = (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;
		if (SurrogateMin <= l && l <= SurrogateMax)
			goto bad;
		*rune = (Rune)l;
		return 3;
	}

	/*
	 * four character sequence (21-bit value)
	 *	10000-1FFFFF => T4 Tx Tx Tx
	 */
	c3 = *(uchar*)(str+3) ^ Tx;
	if (c3 & Testx)
		goto bad;
	if (c < T5) {
		l = ((((((c << Bitx) | c1) << Bitx) | c2) << Bitx) | c3) & Rune4;
		if (l <= Rune3 || l > Runemax)
			goto bad;
		*rune = (Rune)l;
		return 4;
	}

	/*
	 * Support for 5-byte or longer UTF-8 would go here, but
	 * since we don't have that, we'll just fall through to bad.
	 */

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

int
isvalidcharntorune(const char* str, int length, Rune* rune, int* consumed)
{
	*consumed = charntorune(rune, str, length);
	return *rune != Runeerror || *consumed == 3;
}

int
runetochar(char *str, const Rune *rune)
{
	/* Runes are signed, so convert to unsigned for range check. */
	unsigned long c;

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

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

	/*
	 * If the Rune is out of range or a surrogate half, convert it to the error rune.
	 * Do this test here 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.
	 */
	if (c > Runemax)
		c = Runeerror;
	if (SurrogateMin <= c && c <= SurrogateMax)
		c = Runeerror;

	/*
	 * three character sequence
	 *	0800-FFFF => T3 Tx Tx
	 */
	if (c <= Rune3) {
		str[0] = (char)(T3 |  (c >> 2*Bitx));
		str[1] = (char)(Tx | ((c >> 1*Bitx) & Maskx));
		str[2] = (char)(Tx |  (c & Maskx));
		return 3;
	}

	/*
	 * four character sequence (21-bit value)
	 *     10000-1FFFFF => T4 Tx Tx Tx
	 */
	str[0] = (char)(T4 | (c >> 3*Bitx));
	str[1] = (char)(Tx | ((c >> 2*Bitx) & Maskx));
	str[2] = (char)(Tx | ((c >> 1*Bitx) & Maskx));
	str[3] = (char)(Tx | (c & Maskx));
	return 4;
}

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

	return runetochar(str, &rune);
}

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

	nb = 0;
	while(nrune--) {
		c = (int)*r++;
		if (c <= Rune1)
			nb++;
		else if (c <= Rune2)
			nb += 2;
		else if (c <= Rune3)
			nb += 3;
		else /* assert(c <= Rune4) */
			nb += 4;
	}
	return nb;
}

int
fullrune(const char *str, int n)
{
	if (n > 0) {
		int c = *(uchar*)str;
		if (c < Tx)
			return 1;
		if (n > 1) {
			if (c < T3)
				return 1;
			if (n > 2) {
				if (c < T4 || n > 3)
					return 1;
			}
		}
	}
	return 0;
}