feat: implemented errno, strtol. Started ustar. Reformatted headers and

code. Added some self-tests. Started prepwork for vfs.

kernel/libc/stdlib.c

@@ -6,6 +6,8 @@
  */
 
 #include <stdlib.h>
+#include <limits.h>
+#include <errno.h>
 
 /* everything of stdlib is implemented in this file except for:
  * - qsort
@@ -76,3 +78,57 @@ char *itoa(int value, char *buffer, int base) {
     // reverse the string and return it
     return reverse(buffer, 0, i - 1);
 }
+
+long strtol(const char *nptr, char **endptr, int base) {
+    if (base > 36) {
+        errno = EINVAL;
+        return -1;
+    }
+    char sign = '+';
+    long n = 0;
+    long i;
+    const char *c = nptr;
+    while (*c == ' ') {
+        c++;
+    }
+    if (*c == '+') {
+        c++;
+    } else if (*c == '-') {
+        sign = '-';
+        c++;
+    }
+    while (*c != '\0') {
+        n *= base;
+        if (*c >= '0' && *c <= '9') {
+            i = *c - '0';
+        } else if (*c >= 'a' && *c <= 'z') {
+            i = *c - 'a' + 10;
+        } else if (*c >= 'A' && *c <= 'Z') {
+            i = *c - 'A' + 10;
+        } else {
+            errno = EINVAL;
+            n = -1;
+            goto _set_endptr;
+        }
+        if (i >= base) {
+            errno = EINVAL;
+            n = -1;
+            goto _set_endptr;
+        }
+        if (i > (LONG_MAX - n)) {
+            errno = ERANGE;
+            n = sign == '-' ? LONG_MIN : LONG_MAX;
+            goto _set_endptr;
+        }
+        n += i;
+        c++;
+    }
+    if (sign == '-') {
+        n *= -1;
+    }
+    _set_endptr:
+    if (endptr != NULL) {
+        *endptr = c;
+    }
+    return n;
+}