C - AtoF: Convert string to its double-precision floating-point equivalent

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/*
 * AtoF: Convert string to its double-precision floating-point equivalent.
 *
 * AtoF.c - by FreeMan
 */

#include <ctype.h>

double AtoF(char s[])
{
	double val, power;
	int i, sign;
	for (i = 0; isspace(s[i]); i++) /* Skip white space */
		;
	sign = (s[i] == '-') ? -1 : 1;
	if (s[i] == '+' || s[i] == '-')
	{
		i++;
	}
	for (val = 0.0; isdigit(s[i]); i++)
	{
		val = 10.0 * val + (s[i] - '0');
	}
	if (s[i] == '.')
	{
		i++;
	}
	for (power = 1.0; isdigit(s[i]); i++) {
		val = 10.0 * val + (s[i] - '0');
		power *= 10;
	}
	return sign * val / power;
}