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	charstod.c - 9base - revived minimalist port of Plan 9 userland to Unix
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	charstod.c (1309B)
	---
	1 /* Copyright (c) 2002-2006 Lucent Technologies; see LICENSE */
	2 #include <stdarg.h>
	3 #include <string.h>
	4 #include "plan9.h"
	5 #include "fmt.h"
	6 #include "fmtdef.h"
	7
	8 /*
	9 * Reads a floating-point number by interpreting successive characters
	10 * returned by (*f)(vp). The last call it makes to f terminates the
	11 * scan, so is not a character in the number. It may therefore be
	12 * necessary to back up the input stream up one byte after calling chars…
	13 */
	14
	15 double
	16 fmtcharstod(int(f)(void), void *vp)
	17 {
	18 double num, dem;
	19 int neg, eneg, dig, exp, c;
	20
	21 num = 0;
	22 neg = 0;
	23 dig = 0;
	24 exp = 0;
	25 eneg = 0;
	26
	27 c = (*f)(vp);
	28 while(c == ' ' \|\| c == '\t')
	29 c = (*f)(vp);
	30 if(c == '-' \|\| c == '+'){
	31 if(c == '-')
	32 neg = 1;
	33 c = (*f)(vp);
	34 }
	35 while(c >= '0' && c <= '9'){
	36 num = num*10 + c-'0';
	37 c = (*f)(vp);
	38 }
	39 if(c == '.')
	40 c = (*f)(vp);
	41 while(c >= '0' && c <= '9'){
	42 num = num*10 + c-'0';
	43 dig++;
	44 c = (*f)(vp);
	45 }
	46 if(c == 'e' \|\| c == 'E'){
	47 c = (*f)(vp);
	48 if(c == '-' \|\| c == '+'){
	49 if(c == '-'){
	50 dig = -dig;
	51 eneg = 1;
	52 }
	53 c = (*f)(vp);
	54 }
	55 while(c >= '0' && c <= '9'){
	56 exp = exp*10 + c-'0';
	57 c = (*f)(vp);
	58 }
	59 }
	60 exp -= dig;
	61 if(exp < 0){
	62 exp = -exp;
	63 eneg = !eneg;
	64 }
	65 dem = __fmtpow10(exp);
	66 if(eneg)
	67 num /= dem;
	68 else
	69 num *= dem;
	70 if(neg)
	71 return -num;
	72 return num;
	73 }