libc: Implement atoi(), atol() and atoll()

Exactly the same as _exit, but in stdlib.h instead of unistd.h

libs/libc/include/stdlib.h

@@ -15,11 +15,20 @@ extern "C"
     /* Normally exits the program with the specified status code. */
     __lc_noreturn void exit(int status);
 
+    /* Abnormally exits the program with the specified status code. */
+    __lc_noreturn void _Exit(int status);
+
     /* Registers a handler function to be run at normal program termination. */
     int atexit(void (*handler)(void));
 
-    /* Not implemented.*/
-    int atoi(const char*);
+    /* Returns an integer (of type int) parsed from the string str. */
+    int atoi(const char* str);
+
+    /* Returns an integer (of type long) parsed from the string str. */
+    long atol(const char* str);
+
+    /* Returns an integer (of type long long) parsed from the string str. */
+    long long atoll(const char* str);
 
     /* Not implemented. */
     char* getenv(const char*);

libs/libc/src/stdlib.cpp

@@ -1,22 +1,59 @@
+#include <ctype.h>
 #include <luna.h>
 #include <stdlib.h>
 #include <sys/syscall.h>
 #include <unistd.h>
 
+template <typename T> T string_to_integer_type(const char* str)
+{
+    bool neg = false;
+    T val = 0;
+
+    switch (*str)
+    {
+    case '-':
+        neg = true;
+        str++;
+        break;
+    case '+': str++; break;
+    default: break;
+    }
+
+    while (isdigit(*str)) { val = (10 * val) + (*str++ - '0'); }
+
+    return (neg ? -val : val);
+}
+
 extern "C"
 {
     __lc_noreturn void abort()
     {
-        _exit(-1);
+        _Exit(-1);
     }
 
-    int atoi(const char*)
+    int atoi(const char* str)
     {
-        NOT_IMPLEMENTED("atoi");
+        return string_to_integer_type<int>(str);
+    }
+
+    long atol(const char* str)
+    {
+        return string_to_integer_type<long>(str);
+    }
+
+    long long atoll(const char* str)
+    {
+        return string_to_integer_type<long long>(str);
     }
 
     char* getenv(const char*)
     {
         NOT_IMPLEMENTED("getenv");
     }
+
+    __lc_noreturn void _Exit(int status)
+    {
+        syscall(SYS_exit, status);
+        __lc_unreachable();
+    }
 }