/*
 *				e s c . c
 */

/*)LIBRARY
*/

#ifdef	DOCUMENTATION

title	esc	Process Escaped Characters
index		Process escaped characters

synopsis

	 char esc(ppc)
	 char **ppc;

	 int esc_msk;

description

	esc(ppc) recognizes and processes the escaped characters recognized by
	the C compiler.  If *ppc points to any character other than '\', esc()
	just returns that character.  Otherwise, it examines the next
	character.  If it finds a member of the set {b,f,n,r,t}, the
	appropriate character is returned, e.g., a <TAB> for '\t'. Also, \ddd,
	ddd being up to three octal digits, returns the character with value
	ddd.  Only the bottom 8 bits are retained, so the result is always a
	"proper" character.  This can be changed by changing the global
	esc_msk to contain whatever mask you prefer.  (The default is 0377.)

	The special characters b, f, and so on are recognized in lower case
	only.

	If '\' is the last character in s, '\' itself is returned.

	If '\' is followed by any other character x, x itself is returned.

	In all cases, *ppc is left pointing at the last character that esc()
	has "eaten", e.g., at the 't' if it is returning a <TAB> for '\t'.

bugs

author

	Jerry Leichter

#endif

/*
 * )EDITLEVEL=17
 * Edit history
 * 0.0  1-May-81 JSL	Invention
 * 0.1 28-May-81 JSL	Conversion to new comment convention
 * 0.2 23-Jun-81 JSL	escmsk ==> esc_msk
 * 0.3 29-Dec-81 MM	Redone for vax c
 * 0.4 13-Jul-82 JSL	Change esc_msk default to 0377 to support XASCII
 */

#define ESCAPE '\\'
#define EOS '\0'

int esc_msk = 0377;

char
esc(ppc)
char **ppc;
{
	register char c,c1;
	register char	*pc;

	pc = *ppc;
	if ((c = pc[0]) != ESCAPE || pc[1] == EOS)
		return(c);
	else
		c = *++pc;
		*ppc = pc;
		switch(c)
	{
	case 'b':
		return('\b');
	case 'f':
		return('\f');
	case 'n':
		return('\n');
	case 'r':
		return('\r');
	case 't':
		return('\t');
	case '0':
	case '1':
	case '2':
	case '3':
	case '4':
	case '5':
	case '6':
	case '7':
		c -= '0';
		if ((c1 = pc[1]) >= '0' && c1 <= '7' )
		{	c = (c << 3) | (c1 - '0');
			pc++;
			if ((c1 = pc[1]) >= '0' && c1 <= '7' )
			{	c = (c << 3) | (c1 - '0');
				pc++;
			}
		}
		*ppc = pc;
		return(c & esc_msk);
	default:
		return(c);
	}
}