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#include <u.h>
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#include <libc.h>
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/*
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 * Reads a floating-point number by interpreting successive characters
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 * returned by (*f)(vp).  The last call it makes to f terminates the
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 * scan, so is not a character in the number.  It may therefore be
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 * necessary to back up the input stream up one byte after calling charstod.
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 */
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#define ADVANCE *s++ = c; if(s>=e) return NaN(); c = (*f)(vp)
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double
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charstod(int(*f)(void*), void *vp)
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{
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	char str[400], *s, *e, *start;
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	int c;
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	s = str;
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	e = str + sizeof str - 1;
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	c = (*f)(vp);
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	while(c == ' ' || c == '\t')
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		c = (*f)(vp);
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	if(c == '-' || c == '+'){
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		ADVANCE;
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	}
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	start = s;
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	while(c >= '0' && c <= '9'){
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		ADVANCE;
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	}
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	if(c == '.'){
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		ADVANCE;
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		while(c >= '0' && c <= '9'){
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			ADVANCE;
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		}
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	}
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	if(s > start && (c == 'e' || c == 'E')){
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		ADVANCE;
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		if(c == '-' || c == '+'){
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			ADVANCE;
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		}
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		while(c >= '0' && c <= '9'){
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			ADVANCE;
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		}
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	}else if(s == start && (c == 'i' || c == 'I')){
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		ADVANCE;
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		if(c != 'n' && c != 'N')
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			return NaN();
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		ADVANCE;
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		if(c != 'f' && c != 'F')
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			return NaN();
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		ADVANCE;
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		if(c != 'i' && c != 'I')
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			return NaN();
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		ADVANCE;
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		if(c != 'n' && c != 'N')
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			return NaN();
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		ADVANCE;
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		if(c != 'i' && c != 'I')
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			return NaN();
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		ADVANCE;
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		if(c != 't' && c != 'T')
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			return NaN();
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		ADVANCE;
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		if(c != 'y' && c != 'Y')
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			return NaN();
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		ADVANCE;  /* so caller can back up uniformly */
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		USED(c);
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	}else if(s == str && (c == 'n' || c == 'N')){
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		ADVANCE;
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		if(c != 'a' && c != 'A')
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			return NaN();
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		ADVANCE;
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		if(c != 'n' && c != 'N')
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			return NaN();
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		ADVANCE;  /* so caller can back up uniformly */
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		USED(c);
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	}
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	*s = 0;
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	return strtod(str, &s);
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}