diff --git a/src/lol/math/bigint.h b/src/lol/math/bigint.h
index 624a9a18..8b37e923 100644
--- a/src/lol/math/bigint.h
+++ b/src/lol/math/bigint.h
@@ -25,7 +25,7 @@
 namespace lol
 {
 
-/* This is OUR namespace. Don't let Windows headers fuck with it. */
+/* This is OUR namespace. Don't let Windows headers mess with it. */
 #undef min
 #undef max
 
diff --git a/src/lol/math/functions.h b/src/lol/math/functions.h
index 21f68c96..39c119b4 100644
--- a/src/lol/math/functions.h
+++ b/src/lol/math/functions.h
@@ -29,7 +29,7 @@
 namespace lol
 {
 
-/* This is OUR namespace. Don't let Windows headers fuck with it. */
+/* This is OUR namespace. Don't let Windows headers mess with it. */
 #undef min
 #undef max
 
@@ -256,7 +256,8 @@ LOL_ATTR_NODISCARD static inline ldouble round(ldouble x) { return std::round(x)
     LOL_ATTR_NODISCARD static inline T min(T x, T y) { return std::min(x, y); } \
     LOL_ATTR_NODISCARD static inline T max(T x, T y) { return std::max(x, y); } \
     LOL_ATTR_NODISCARD static inline T clamp(T x, T y, T z) { return min(max(x, y), z); } \
-    LOL_ATTR_NODISCARD static inline T saturate(T x) { return min(max(x, (T)0), (T)1); }
+    LOL_ATTR_NODISCARD static inline T saturate(T x) { return min(max(x, (T)0), (T)1); } \
+    LOL_ATTR_NODISCARD static inline T gcd(T x, T y) { return y == (T)0 ? lol::abs(x) : lol::gcd(y, lol::fmod(x, y)); }
 
 #define LOL_GENERIC_FUNC_SIGNED(T) \
     LOL_GENERIC_FUNC(T) \
diff --git a/src/lol/math/half.h b/src/lol/math/half.h
index dcf3dbfe..bba0919e 100644
--- a/src/lol/math/half.h
+++ b/src/lol/math/half.h
@@ -24,7 +24,7 @@
 namespace lol
 {
 
-/* This is OUR namespace. Don't let Windows headers fuck with it. */
+/* This is OUR namespace. Don't let Windows headers mess with it. */
 #undef min
 #undef max
 
diff --git a/src/lol/math/real.h b/src/lol/math/real.h
index f8cb4e02..4f22515e 100644
--- a/src/lol/math/real.h
+++ b/src/lol/math/real.h
@@ -24,7 +24,7 @@
 namespace lol
 {
 
-/* This is OUR namespace. Don't let Windows headers fuck with it. */
+/* This is OUR namespace. Don't let Windows headers mess with it. */
 #undef min
 #undef max
 
diff --git a/src/t/Makefile.am b/src/t/Makefile.am
index 3ea42ff3..1dba7868 100644
--- a/src/t/Makefile.am
+++ b/src/t/Makefile.am
@@ -37,7 +37,7 @@ test_math_SOURCES = test-common.cpp \
     math/cmplx.cpp math/half.cpp math/interp.cpp math/matrix.cpp \
     math/quat.cpp math/rand.cpp math/real.cpp math/rotation.cpp \
     math/trig.cpp math/vector.cpp math/polynomial.cpp math/noise/simplex.cpp \
-    math/bigint.cpp math/sqt.cpp
+    math/bigint.cpp math/sqt.cpp math/numbers.cpp
 test_math_CPPFLAGS = $(AM_CPPFLAGS) -I$(top_srcdir)/tools/lolunit
 test_math_DEPENDENCIES = @LOL_DEPS@
 
diff --git a/src/t/math/numbers.cpp b/src/t/math/numbers.cpp
new file mode 100644
index 00000000..958de324
--- /dev/null
+++ b/src/t/math/numbers.cpp
@@ -0,0 +1,44 @@
+//
+//  Lol Engine — Unit tests for number theory
+//
+//  Copyright © 2010—2018 Sam Hocevar <sam@hocevar.net>
+//
+//  Lol Engine is free software. It comes without any warranty, to
+//  the extent permitted by applicable law. You can redistribute it
+//  and/or modify it under the terms of the Do What the Fuck You Want
+//  to Public License, Version 2, as published by the WTFPL Task Force.
+//  See http://www.wtfpl.net/ for more details.
+//
+
+#include <lol/engine-internal.h>
+
+#include <lolunit.h>
+
+namespace lol
+{
+
+lolunit_declare_fixture(gcd_test)
+{
+    lolunit_declare_test(gcd_int)
+    {
+        lolunit_assert_equal(1, lol::gcd(37, 600));
+        lolunit_assert_equal(2, lol::gcd(4, 6));
+        lolunit_assert_equal(2, lol::gcd(6, 4));
+        lolunit_assert_equal(13, lol::gcd(13, 13));
+        lolunit_assert_equal(20, lol::gcd(20, 100));
+        lolunit_assert_equal(18913, lol::gcd(624129, 2061517));
+    }
+
+    lolunit_declare_test(gcd_negative)
+    {
+        lolunit_assert_equal(2, lol::gcd(4, -6));
+        lolunit_assert_equal(2, lol::gcd(-4, 6));
+        lolunit_assert_equal(2, lol::gcd(-4, -6));
+        lolunit_assert_equal(2, lol::gcd(6, -4));
+        lolunit_assert_equal(2, lol::gcd(-6, 4));
+        lolunit_assert_equal(2, lol::gcd(-6, -4));
+    }
+};
+
+} /* namespace lol */
+
diff --git a/src/t/test-math.vcxproj b/src/t/test-math.vcxproj
index a1ec3464..1fdc0b02 100644
--- a/src/t/test-math.vcxproj
+++ b/src/t/test-math.vcxproj
@@ -42,6 +42,7 @@
     <ClCompile Include="math\interp.cpp" />
     <ClCompile Include="math\matrix.cpp" />
     <ClCompile Include="math\noise\simplex.cpp" />
+    <ClCompile Include="math\numbers.cpp" />
     <ClCompile Include="math\polynomial.cpp" />
     <ClCompile Include="math\quat.cpp" />
     <ClCompile Include="math\rand.cpp" />