Implemented a proper version of strtoul()

photon/libc/stdlib/strtoul.c

@@ -5,5 +5,70 @@
 
 unsigned long strtoul(const char *nptr, char **endptr, int base)
 {
-    return (unsigned long)strtol(nptr, endptr, base);
+    const char *s = nptr;
+    unsigned long acc;
+    int c;
+    unsigned long cutoff;
+    int neg = 0, any, cutlim;
+
+    do {
+        c = *s++;
+    } while (isspace(c));
+
+    if (c == '-') {
+        neg = 1;
+        c = *s++;
+    } else if (c == '+') {
+        c = *s++;
+    } if ((base == 0 || base == 16) &&
+        c == '0' && (*s == 'x' || *s == 'X')) {
+        c = s[1];
+        s += 2;
+        base = 16;
+    } else if ((base == 0 || base == 2) &&
+        c == '0' && (*s == 'b' || *s == 'B')) {
+        c = s[1];
+        s += 2;
+        base = 2;
+    }
+
+    if (base == 0) {
+        base = c == '0' ? 8 : 10;
+    }
+
+    cutoff = ULONG_MAX;
+    cutlim = cutoff % (unsigned long)base;
+    cutoff /= (unsigned long)base;
+
+    for (acc = 0, any = 0;; c = *s++) {
+        if (isdigit(c)) {
+            c -= '0';
+        } else if (isalpha(c)) {
+            c -= isupper(c) ? 'A' - 10 : 'a' - 10;
+        } else {
+            break;
+        }
+
+        if (c >= base) {
+            break;
+        } if (any < 0 || acc > cutoff || acc == cutoff && c > cutlim) {
+            any = -1;
+        } else {
+            any = 1;
+            acc *= base;
+            acc += c;
+        }
+    }
+
+    if (any < 0) {
+        acc = ULONG_MAX;
+    } else if (neg) {
+        acc = -acc;
+    }
+
+    if (endptr != 0) {
+        *endptr = (char *)(any ? s - 1 : nptr);
+    }
+
+    return acc;
 }