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diff --git a/src/helper/mathfns.h b/src/helper/mathfns.h
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+// SPDX-License-Identifier: GPL-2.0-or-later
+/**
+ * Mathematical/numerical functions.
+ *
+ * Authors:
+ *   Johan Engelen <goejendaagh@zonnet.nl>
+ *
+ * Copyright (C) 2007 Johan Engelen
+ *
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+
+#ifndef INKSCAPE_HELPER_MATHFNS_H
+#define INKSCAPE_HELPER_MATHFNS_H
+
+#include <cmath>
+#include <2geom/point.h>
+
+namespace Inkscape {
+namespace Util {
+
+/**
+ * \return x rounded to the nearest multiple of c1 plus c0.
+ *
+ * \note
+ * If c1==0 (and c0 is finite), then returns +/-inf.  This makes grid spacing of zero
+ * mean "ignore the grid in this dimension".
+ */
+inline double round_to_nearest_multiple_plus(double x, double c1, double c0)
+{
+    return std::floor((x - c0) / c1 + 0.5) * c1 + c0;
+}
+
+/**
+ * \return x rounded to the lower multiple of c1 plus c0.
+ *
+ * \note
+ * If c1 == 0 (and c0 is finite), then returns +/-inf. This makes grid spacing of zero
+ * mean "ignore the grid in this dimension".
+ */
+inline double round_to_lower_multiple_plus(double x, double c1, double c0 = 0.0)
+{
+    return std::floor((x - c0) / c1) * c1 + c0;
+}
+
+/**
+ * \return x rounded to the upper multiple of c1 plus c0.
+ *
+ * \note
+ * If c1 == 0 (and c0 is finite), then returns +/-inf. This makes grid spacing of zero
+ * mean "ignore the grid in this dimension".
+ */
+inline double round_to_upper_multiple_plus(double x, double const c1, double const c0 = 0)
+{
+    return std::ceil((x - c0) / c1) * c1 + c0;
+}
+
+/// Returns floor(log_2(x)), assuming x >= 1.
+// Note: This is a naive implementation.
+// Todo: (C++20) Replace with std::bit_floor.
+template <typename T>
+int constexpr floorlog2(T x)
+{
+    int n = -1;
+    while (x > 0) {
+        x /= 2;
+        n++;
+    }
+    return n;
+}
+
+/// Returns \a a mod \a b, always in the range 0..b-1, assuming b >= 1.
+template <typename T, typename std::enable_if<std::is_integral<T>::value, bool>::type = true>
+T constexpr safemod(T a, T b)
+{
+    a %= b;
+    return a < 0 ? a + b : a;
+}
+
+/// Returns \a a rounded down to the nearest multiple of \a b, assuming b >= 1.
+template <typename T, typename std::enable_if<std::is_integral<T>::value, bool>::type = true>
+T constexpr rounddown(T a, T b)
+{
+    return a - safemod(a, b);
+}
+
+/// Returns \a a rounded up to the nearest multiple of \a b, assuming b >= 1.
+template <typename T, typename std::enable_if<std::is_integral<T>::value, bool>::type = true>
+T constexpr roundup(T a, T b)
+{
+    return rounddown(a - 1, b) + b;
+}
+
+/**
+ * Just like std::clamp, except it doesn't deliberately crash if lo > hi due to rounding errors,
+ * so is safe to use with floating-point types. (Note: compiles to branchless.)
+ */
+template <typename T>
+T safeclamp(T val, T lo, T hi)
+{
+    if (val < lo) return lo;
+    if (val > hi) return hi;
+    return val;
+}
+
+} // namespace Util
+} // namespace Inkscape
+
+#endif // INKSCAPE_HELPER_MATHFNS_H
+
+/*
+  Local Variables:
+  mode:c++
+  c-file-style:"stroustrup"
+  c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
+  indent-tabs-mode:nil
+  fill-column:99
+  End:
+*/
+// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:fileencoding=utf-8:textwidth=99 :