1 files changed, 72 insertions, 0 deletions
diff --git a/include/o3tl/float_int_conversion.hxx b/include/o3tl/float_int_conversion.hxx
new file mode 100644
index 000000000..403bed622
--- /dev/null
+++ b/include/o3tl/float_int_conversion.hxx
@@ -0,0 +1,72 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
+/*
+ * 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_FLOAT_INT_CONVERSION_HXX
+#define INCLUDED_O3TL_FLOAT_INT_CONVERSION_HXX
+
+#include <sal/config.h>
+
+#include <cmath>
+#include <limits>
+#include <type_traits>
+
+namespace o3tl
+{
+// Return true iff `value` of floating-point type `F` converts to a value of integral type `I` no
+// smaller than `min`:
+template <typename F, typename I>
+constexpr std::enable_if_t<std::is_floating_point_v<F> && std::is_integral_v<I>, bool>
+convertsToAtLeast(F value, I min)
+{
+    // If `F(min)`, `F(min) - F(1)` are too large in magnitude for `F`'s precision, then they either
+    // fall into the same bucket, in which case we should return false if `value` represents that
+    // bucket, or they are on the boundary of two adjacent buckets, in which case we should return
+    // true if `value`represents the higher bucket containing `F(min)`:
+    return value > F(min) - F(1);
+}
+
+// Return true iff `value` of floating-point type `F` converts to a value of integral type `I` no
+// larger than `max`:
+template <typename F, typename I>
+constexpr std::enable_if_t<std::is_floating_point_v<F> && std::is_integral_v<I>, bool>
+convertsToAtMost(F value, I max)
+{
+    // If `F(max)`, `F(max) + F(1)` are too large in magnitude for `F`'s precision, then they either
+    // fall into the same bucket, in which case we should return false if `value` represents that
+    // bucket, or they are on the boundary of two adjacent buckets, in which case we should return
+    // true if `value`represents the lower bucket containing `F(max)`:
+    return value < F(max) + F(1);
+}
+
+// Casts a floating-point to an integer, avoiding overflow. Used like:
+//     sal_Int64 n = o3tl::saturating_cast<sal_Int64>(f);
+template <typename I, typename F>
+constexpr std::enable_if_t<std::is_floating_point_v<F> && std::is_integral_v<I>, I>
+saturating_cast(F f)
+{
+    if constexpr (std::is_signed_v<I>)
+        if (!convertsToAtLeast(f, std::numeric_limits<I>::min()))
+            return std::numeric_limits<I>::min();
+    if (!convertsToAtMost(f, std::numeric_limits<I>::max()))
+        return std::numeric_limits<I>::max();
+    return f;
+}
+
+// Return `value` of floating-point type `F` rounded to the nearest integer away from zero (which
+// can be useful in calls to convertsToAtLeast/Most(roundAway(x), n), to reject x that are
+// smaller/larger than n because they have a fractional part):
+template <typename F> std::enable_if_t<std::is_floating_point_v<F>, F> roundAway(F value)
+{
+    return value >= 0 ? std::ceil(value) : std::floor(value);
+}
+}
+
+#endif
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */