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#include <u.h>
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#include <libc.h>
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#include "fmtdef.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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double
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fmtcharstod(int(*f)(void*), void *vp)
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{
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	double num, dem;
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	int neg, eneg, dig, exp, c;
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	num = 0;
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	neg = 0;
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	dig = 0;
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	exp = 0;
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	eneg = 0;
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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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		if(c == '-')
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			neg = 1;
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		c = (*f)(vp);
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	}
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	while(c >= '0' && c <= '9'){
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		num = num*10 + c-'0';
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		c = (*f)(vp);
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	}
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	if(c == '.')
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		c = (*f)(vp);
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	while(c >= '0' && c <= '9'){
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		num = num*10 + c-'0';
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		dig++;
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		c = (*f)(vp);
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	}
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	if(c == 'e' || c == 'E'){
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		c = (*f)(vp);
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		if(c == '-' || c == '+'){
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			if(c == '-'){
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				dig = -dig;
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				eneg = 1;
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			}
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			c = (*f)(vp);
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		}
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		while(c >= '0' && c <= '9'){
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			exp = exp*10 + c-'0';
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			c = (*f)(vp);
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		}
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	}
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	exp -= dig;
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	if(exp < 0){
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		exp = -exp;
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		eneg = !eneg;
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	}
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	dem = __fmtpow10(exp);
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	if(eneg)
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		num /= dem;
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	else
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		num *= dem;
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	if(neg)
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		return -num;
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	return num;
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}