check for overflow in multiply

gcc >= 5 and clang have builtins for this
msvc has safeint.h and functions in the msl::utilties namespace
otherwise fall back to certs demo implementations

Change-Id: I6001a278c24b0be4b381d933d256f01f91ead55d
Reviewed-on: https://gerrit.libreoffice.org/35505
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

1 files changed, 89 insertions, 0 deletions

diff --git a/include/o3tl/safeint.hxx b/include/o3tl/safeint.hxx
new file mode 100644
index 000000000000..552c834bd6a9
--- /dev/null
+++ b/include/o3tl/safeint.hxx
@@ -0,0 +1,89 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef INCLUDED_O3TL_SAFE_INT_HXX
+#define INCLUDED_O3TL_SAFE_INT_HXX
+
+#include <limits>
+#if defined(_MSC_VER)
+#include <safeint.h>
+#else
+#ifndef __has_builtin
+#   define __has_builtin(x) 0
+#endif
+#endif
+
+namespace o3tl
+{
+
+#if defined(_MSC_VER)
+
+template<typename T> inline bool checked_multiply(T a, T b, T& result)
+{
+    return !msl::utilities::SafeMultiply(a, b, result);
+}
+
+#elif (defined __GNUC__ && __GNUC__ >= 5) || (__has_builtin(__builtin_mul_overflow))
+
+template<typename T> inline bool checked_multiply(T a, T b, T& result)
+{
+    return __builtin_mul_overflow(a, b, &result);
+}
+
+#else
+
+//https://www.securecoding.cert.org/confluence/display/c/INT32-C.+Ensure+that+operations+on+signed+integers+do+not+result+in+overflow
+template<typename T> inline typename std::enable_if<std::is_signed<T>::value, bool>::type checked_multiply(T a, T b, T& result)
+{
+  if (a > 0) {  /* a is positive */
+    if (b > 0) {  /* a and b are positive */
+      if (a > (std::numeric_limits<T>::max() / b)) {
+        return true; /* Handle error */
+      }
+    } else { /* a positive, b nonpositive */
+      if (b < (std::numeric_limits<T>::min() / a)) {
+        return true; /* Handle error */
+      }
+    } /* a positive, b nonpositive */
+  } else { /* a is nonpositive */
+    if (b > 0) { /* a is nonpositive, b is positive */
+      if (a < (std::numeric_limits<T>::min() / b)) {
+        return true; /* Handle error */
+      }
+    } else { /* a and b are nonpositive */
+      if ( (a != 0) && (b < (std::numeric_limits<T>::max() / a))) {
+        return true; /* Handle error */
+      }
+    } /* End if a and b are nonpositive */
+  } /* End if a is nonpositive */
+
+  result = a * b;
+
+  return false;
+}
+
+//https://www.securecoding.cert.org/confluence/display/c/INT30-C.+Ensure+that+unsigned+integer+operations+do+not+wrap
+template<typename T> inline typename std::enable_if<std::is_unsigned<T>::value, bool>::type checked_multiply(T a, T b, T& result)
+{
+    if (b && a > std::numeric_limits<T>::max() / b) {
+        return true;/* Handle error */
+    }
+
+    result = a * b;
+
+    return false;
+}
+
+#endif
+
+}
+
+#endif
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */