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#include "a.h"
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/*
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 * 16. Conditional acceptance of input.
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 *
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 *	conditions are
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 *		c - condition letter (o, e, t, n)
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 *		!c - not c
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 *		N - N>0
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 *		!N - N <= 0
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 *		'a'b' - if a==b
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 *		!'a'b'	- if a!=b
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 *
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 *	\{xxx\} can be used for newline in bodies
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 *
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 *	.if .ie .el
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 *
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 */
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int iftrue[20];
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int niftrue;
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void
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startbody(void)
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{
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	int c;
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	while((c = getrune()) == ' ' || c == '\t')
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		;
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	ungetrune(c);
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}
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void
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skipbody(void)
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{
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	int c, cc, nbrace;
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	nbrace = 0;
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	for(cc=0; (c = getrune()) >= 0; cc=c){
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		if(c == '\n' && nbrace <= 0)
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			break;
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		if(cc == '\\' && c == '{')
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			nbrace++;
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		if(cc == '\\' && c == '}')
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			nbrace--;
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	}
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}
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int
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ifeval(void)
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{
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	int c, cc, neg, nc;
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	Rune line[MaxLine], *p, *e, *q;
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	Rune *a;
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	while((c = getnext()) == ' ' || c == '\t')
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		;
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	neg = 0;
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	while(c == '!'){
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		neg = !neg;
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		c = getnext();
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	}
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	if('0' <= c && c <= '9'){
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		ungetnext(c);
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		a = copyarg();
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		c = (eval(a)>0) ^ neg;
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		free(a);
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		return c;
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	}
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	switch(c){
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	case ' ':
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	case '\n':
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		ungetnext(c);
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		return !neg;
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	case 'o':	/* odd page */
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	case 't':	/* troff */
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	case 'h':	/* htmlroff */
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		while((c = getrune()) != ' ' && c != '\t' && c != '\n' && c >= 0)
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			;
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		return 1 ^ neg;
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	case 'n':	/* nroff */
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	case 'e':	/* even page */
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		while((c = getnext()) != ' ' && c != '\t' && c != '\n' && c >= 0)
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			;
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		return 0 ^ neg;
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	}
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	/* string comparison 'string1'string2' */
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	p = line;
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	e = p+nelem(line);
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	nc = 0;
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	q = nil;
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	while((cc=getnext()) >= 0 && cc != '\n' && p<e){
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		if(cc == c){
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			if(++nc == 2)
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				break;
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			q = p;
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		}
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		*p++ = cc;
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	}
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	if(cc != c){
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		ungetnext(cc);
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		return 0;
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	}
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	if(nc < 2){
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		return 0;
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	}
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	*p = 0;
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	return (q-line == p-(q+1)
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		&& memcmp(line, q+1, (q-line)*sizeof(Rune))==0) ^ neg;
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}
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void
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r_if(Rune *name)
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{
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	int n;
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	n = ifeval();
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	if(runestrcmp(name, L("ie")) == 0){
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		if(niftrue >= nelem(iftrue))
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			sysfatal("%Cie overflow", dot);
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		iftrue[niftrue++] = n;
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	}
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	if(n)
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		startbody();
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	else
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		skipbody();
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}
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void
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r_el(Rune *name)
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{
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	USED(name);
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	if(niftrue <= 0){
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		warn("%Cel underflow", dot);
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		return;
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	}
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	if(iftrue[--niftrue])
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		skipbody();
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	else
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		startbody();
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}
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void
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t16init(void)
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{
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	addraw(L("if"), r_if);
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	addraw(L("ie"), r_if);
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	addraw(L("el"), r_el);
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	addesc('{', e_nop, HtmlMode|ArgMode);
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	addesc('}', e_nop, HtmlMode|ArgMode);
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}