1 files changed, 50 insertions, 0 deletions
diff --git a/nss/nat.c b/nss/nat.c
new file mode 100644
index 0000000..dc6b648
--- /dev/null
+++ b/nss/nat.c
@@ -0,0 +1,50 @@
+#define _GNU_SOURCE
+#include <errno.h>
+#include <stdio.h>
+#include <syslog.h>
+#include <string.h>
+#include <stdlib.h>
+
+#include "cgen.h"
+#include "nat.h"
+
+#include "config/debug.h"
+
+int nat_add(unsigned long* result, unsigned long arg)
+{
+   unsigned long tmp = *result + arg;
+   if (tmp < arg) {
+      errno = EOVERFLOW;
+      return 1;
+   }
+   *result = tmp;
+   return 0;
+}
+
+int nat_mult(unsigned long* result, unsigned long long arg)
+{
+    unsigned long long tmp = arg * (*result);
+    if (tmp > (unsigned long)-1) {
+       errno = EOVERFLOW;
+       return 1;
+    }
+    *result = ((unsigned long) -1) & tmp;
+    return 0;
+}
+
+int parse_nat(unsigned long* result, const char* buf, size_t buflen) {
+  unsigned long total = 0;
+  for (size_t i = 0; i < buflen; i++)
+  {
+      LET(char num = buf[i] - '0', num < 0 || num > 9,
+          "Non-decimal character in string.", out_error_inval);
+      CHK(nat_mult(&total, 10) == 1, "Multiplication overflow.", out_error_errno);
+      CHK(nat_add(&total, num) == 1, "Addition overflow.", out_error_errno);
+  }
+  *result = total;
+  return 0;
+out_error_inval:
+  errno = EINVAL;
+out_error_errno:
+  return 1;
+}