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#include <stdio.h>
/*static int _strlen(char s[]) {
int i;
for (i=0; s[i] != '\0'; i++) {}
return i;
}*/
/*static int _isspace(char s) {
return s == ' ' || s == '\t';
}*/
static int _isdigit(char s) {
return '0' <= s && s <= '9';
}
static int _abs(int a) {
if (a >=0) {
return a;
} else {
return -1 * a;
}
}
static int _intval(char s) {
return s - '0';
}
static int _isupper(char s) {
return 'A' <= s && s <= 'Z';
}
static char _tolower(char s) {
static int diff = 'A' - 'a';
if (_isupper(s)) {
return s - diff;
} else {
return s;
}
}
static int _atoi_internal(char s[], int n) {
if (s == NULL || *s == '\0' || !_isdigit(*s)) {
return n;
}
__attribute__((musttail)) // Functional programinng enabler :)
return _atoi_internal(s + 1, (10 * n) + _intval(*s));
}
/**
* Converts a string to an integer
* string must be null terminated
* overflow isn't detected, int is the limit
*/
int _atoi(char s[]) {
int i = 0;
int sign = (s[i] == '-') ? -1 : 1;
if (s[i] == '+' || s[i] == '-')
i++;
return _atoi_internal(s + i, 0) * sign;
}
/**
* Converts a string to a double
*
* string must be null terminated.
* overflow isn't detected, and double precision is the limit.
*/
double _atof(char s[]) {
double val, power, ee;
int i = 0;
int sign = (s[i] == '-') ? -1 : 1;
if (s[i] == '+' || s[i] == '-')
i++;
for (val = 0.0; _isdigit(s[i]); i++)
val = 10.0 * val + _intval(s[i]);
if (s[i] == '.')
i++;
for (power = 1.0; _isdigit(s[i]); i++) {
val = 10.0 * val + _intval(s[i]);
power *= 10.0;
}
ee = 1.0;
if (_tolower(s[i]) == 'e') {
i++;
int exponent = _atoi(s + i);
if (exponent >= 0) {
for (int j=0;j<_abs(exponent);j++) ee *= 10.0;
} else {
for (int j=0;j<_abs(exponent);j++) ee /= 10.0;
}
}
return (sign * val / power) * ee;
}
void testb(char s[]) {
printf("atoi s = [%s] result = [%d]\n", s, _atoi(s));
}
void test(char s[]) {
printf("atof s = [%s] result = [%lf]\n", s, _atof(s));
}
int main(void) {
test("");
test("gibber");
test("\0");
test("1");
test("1.0");
test("99.0");
test("-10.0");
test("+11.0");
test("++11.0");
test("-11111111111111111111111111111111111111111111111111111111111111111111111111111111111.1");
testb("gibber");
testb("");
testb("\0");
testb("1");
testb("1.5");
testb("+2.6");
testb("-7.8");
testb("--7.8");
test("+11.0e5");
test("2.75345e3");
test("2.75345e-3");
test("2.75345E-3");
}
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