#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <ctype.h>

#ifdef isdigit
#undef isdigit
#endif
#define isdigit(c) ((c) >= '0' && (c) <= '9')

double strtod__(const char *start, char **end);

int main()
{
    // Test case
    char *end, *start = " -12.1 -0.11 124 24.7 212.193";

    end = start;
	while (*start)
		{
		printf("Strtod__ is : %f\n", strtod__(start, &end));
//		printf("Strtod is : %f\n", strtod(start, &end));
		printf("end is : %s\n", end);

        //  prevent infinity loop
		if (start == end)
            break;
		start = end;
		}
    return 0;
}

// Should avoid floating-point operations because
// some processors doesn't has fpu unit
// This causes too big performance degradation on arm
double strtod__(const char *start, char **end){

    printf("Shit start: %s\n", start);
    // skip leading space characters
	while (*start && *start == ' ') {
		start++;
	}

    // is bitwise optation more quick?
	int negate = 1;
	if(*start == '-'){
        negate = -1;
        start++;
	}

    printf("Shit negate: %d\n", negate);
    printf("Shit start: %s\n\n\n", start);

    if(*start == '+')
        start++;

    // sucking integer part
    int retvalue = 0;
    while(isdigit(*start)){
//        printf("sucking start: %s\n", start);
        retvalue *= 10;
        retvalue = retvalue + (*start - '0');
        start++;
    }
//    printf("Parsed integer part value: %d and start: %s\n", retvalue, start);

    if(*start != '.'){
        *end = (char *)start;
        return negate * (double)retvalue;
    }
    else
        start++;

    // sucking decimal fraction part
    int fpsize = 1, fpvalue = 0;
    while(isdigit(*start)){
        fpsize *= 10;
        fpvalue *= 10;
        fpvalue = fpvalue + (*start - '0');
        start++;
    }

    *end = (char *)start;
//    printf("Before return start : %s\n", start);
//    printf("and fpvalue: %f\n", retvalue + fpvalue * 1.0/fpsize);

	return negate * (retvalue + fpvalue * (1.0/fpsize));
}