Add atoi

core/klibc.c

@@ -121,6 +121,34 @@ char *itoa(long long int value, char *str, int base)
     return rc;
 }
 
+int atoi(const char *str)
+{
+    int sign = 1, base = 0, i = 0;
+
+    // if whitespaces then ignore.
+    while (str[i] == ' ') {
+        i++;
+    }
+
+    // sign of number
+    if (str[i] == '-' || str[i] == '+') {
+        sign = 1 - 2 * (str[i++] == '-');
+    }
+
+    // checking for valid input
+    while (str[i] >= '0' && str[i] <= '9') {
+        // handling overflow test case
+        if (base > INT_MAX / 10 || (base == INT_MAX / 10 && str[i] - '0' > 7)) {
+            if (sign == 1)
+                return INT_MAX;
+            else
+                return INT_MIN;
+        }
+        base = 10 * base + (str[i++] - '0');
+    }
+    return base * sign;
+}
+
 /* K&R */
 void reverse(char s[])
 {

core/klibc.h

@@ -15,6 +15,7 @@ int memcmp(const void *s1, const void *s2, size_t n);
 void *memcpy(void *dest, const void *src, size_t n);
 void *memset(void *s, int c, size_t n);
 char *itoa(long long int value, char *str, int base);
+int atoi(const char *str);
 void reverse(char s[]);
 int strlen(const char s[]);
 unsigned int strnlen(const char *s, size_t count);