#include <ctype.h>
#include "string.h"
#include <math.h>

double
strtod(str, ptr)
char *str;
char **ptr;
{
    int sign = 1;
    register char c;
    register char *s = str;
    register char *p;
    register i;
    int expon, expon_s;
    double mult, mant, atof();

    /* Skip whitespace */
    while (isspace(*s))
	s++;

    /* Check for sign */
    c = *s;
    if (c == '+') {
	sign = 1;
	s++;
    } else if (c == '-') {
	sign = -1;
	s++;
    } else if (!isdigit(c)) {
	/* String has to be one of INF INFINITY NAN(string w/o ')') */
	char buf[10];	/* to make a lowercase comparison */
	double big = 1000000.0;
	int slen = strlen(s);

	(void) strncpy(buf, s, 10);
	for (p = buf, i=slen; i-- != 0; p++ ) {
	    if (isupper(*p))
		*p = tolower(*p);
	}

	if (strncmp(buf, "inf", 3) == 0) {
	    if (ptr)
		*ptr = s+3;
	    return (sign * exp(big));
	} else if (strncmp(buf, "infinity",8) == 0) {
	    if (ptr)
		*ptr = s+8;
	    return (sign * exp(big));
	} else if (strncmp(buf, "nan",3) == 0 && *(buf+3) != '(') {
	    if (ptr)
		*ptr = s+3;
	    return (sign * exp(big)) / exp(big);
	} else if (strncmp(buf, "nan(", 4) == 0) {
	    /* Rest has to end in ')' and not include ')' */
	    p = strchr(buf, ')');
	    if (p == (char *) 0) {
		/* No closing ')' */
		if (ptr)
		    *ptr = str;
		return 0.0;
	    }
	    if (ptr)
		*ptr = s + (p + 1 - buf);
	    return exp(big) / exp(big);
	}
    }

    /* To get here: we've got a sign, now need mantissa[+exponent] */
    for (mant = 0.0; isdigit(*s);)
	mant = (mant * 10.0)  +  (*s++ - '0');
    if (*s == '.') {
	/* Collect fraction */
	s++;
	for ( mult = 0.1; isdigit(*s); mult *= 0.1 )
	    mant += (*s++ - '0') * mult;
    }
    /* Check for exponent character */
    c = *s;
    if (c != 'e' && c != 'E' && c != 'd' && c != 'D') {
	if (ptr)
	    *ptr = s;
	return sign * mant;
    }
    /* Check for <sign><digit> or <digit> following exponent character */
    c = *(s+1);
    if (c == '+' || c == '-') {
	if (!isdigit(*(s+2))) {
	    if (ptr)
		*ptr = s;
	    return sign * mant;
	}
    } else if (!isdigit(c)) {
	if (ptr)
	    *ptr = s;
	return sign * mant;
    }
    /* Move past exponent character */
    s++;
    /* Check for sign */
    switch (*s) {
    case '+':
	expon_s = 1;
	s++;
	break;
    case '-':
	expon_s = -1;
	s++;
	break;
    default:
	expon_s = 1;
    }
    /* Collect exponent */
    for (expon = 0; isdigit(*s);)
	expon = (expon * 10)  +  (*s++ - '0');
    if (expon_s == -1)
	expon = -expon;
    if (ptr)
	*ptr = s;
    return  sign * mant * pow(10.0, (double) expon);
}