diff --git a/port_gnu.h b/port_gnu.h
new file mode 100644
index 0000000..8de073c
--- /dev/null
+++ b/port_gnu.h
@@ -0,0 +1,175 @@
+/* Wayland compositor running on top of an X server.
+
+Copyright (C) 2022 to various contributors.
+
+This file is part of 12to11.
+
+12to11 is free software: you can redistribute it and/or modify it
+under the terms of the GNU General Public License as published by the
+Free Software Foundation, either version 3 of the License, or (at your
+option) any later version.
+
+12to11 is distributed in the hope that it will be useful, but WITHOUT
+ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with 12to11.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* Copyright (C) 2001-2022 Free Software Foundation, Inc.
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as
+published by the Free Software Foundation; either version 2.1 of the
+License, or (at your option) any later version.
+
+This program is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public
+License along with this program.
+
+If not, see <https://www.gnu.org/licenses/>.  */
+
+#ifndef IntAddWrapv
+
+#define _GL_INT_CONVERT(e, v)		((1 ? 0 : (e)) + (v))
+#define _GL_INT_NEGATE_CONVERT(e, v)	((1 ? 0 : (e)) - (v))
+#define _GL_TYPE_SIGNED(t)		(! ((t) 0 < (t) -1))
+#define _GL_EXPR_SIGNED(e)		(_GL_INT_NEGATE_CONVERT (e, 1) < 0)
+#define _GL_TYPE_WIDTH(t)		(sizeof (t) * CHAR_BIT)
+
+#define _GL_INT_OP_WRAPV_VIA_UNSIGNED(a, b, op, ut, t)					\
+  ((t) ((ut) (a) op (ut) (b)))
+
+#define _GL_INT_NEGATE_RANGE_OVERFLOW(a, min, max) 					\
+  ((min) < 0 ? (a) < - (max) : 0 < (a))
+
+#define _GL_INT_MINIMUM(e)								\
+  (_GL_EXPR_SIGNED (e)									\
+   ? ~ _GL_SIGNED_INT_MAXIMUM (e)							\
+   : _GL_INT_CONVERT (e, 0))
+
+#define _GL_INT_MAXIMUM(e)								\
+  (_GL_EXPR_SIGNED (e)									\
+   ? _GL_SIGNED_INT_MAXIMUM (e)								\
+   : _GL_INT_NEGATE_CONVERT (e, 1))
+
+#define _GL_SIGNED_INT_MAXIMUM(e)							\
+  (((_GL_INT_CONVERT (e, 1) << (_GL_TYPE_WIDTH (+ (e)) - 2)) - 1) * 2 + 1)
+
+#define _GL_INT_OP_CALC(a, b, r, op, overflow, ut, t, tmin, tmax)			\
+  (overflow (a, b, tmin, tmax)								\
+   ? (*(r) = _GL_INT_OP_WRAPV_VIA_UNSIGNED (a, b, op, ut, t), 1)			\
+   : (*(r) = _GL_INT_OP_WRAPV_VIA_UNSIGNED (a, b, op, ut, t), 0))
+
+# define _GL_INT_NEGATE_OVERFLOW(a)							\
+   _GL_INT_NEGATE_RANGE_OVERFLOW (a, _GL_INT_MINIMUM (a), _GL_INT_MAXIMUM (a))
+
+#define _GL_INT_ADD_RANGE_OVERFLOW(a, b, tmin, tmax)					\
+  ((b) < 0										\
+   ? (((tmin)										\
+       ? ((_GL_EXPR_SIGNED (_GL_INT_CONVERT (a, (tmin) - (b))) || (b) < (tmin))		\
+          && (a) < (tmin) - (b))							\
+       : (a) <= -1 - (b))								\
+      || ((_GL_EXPR_SIGNED (a) ? 0 <= (a) : (tmax) < (a)) && (tmax) < (a) + (b)))	\
+   : (a) < 0										\
+   ? (((tmin)										\
+       ? ((_GL_EXPR_SIGNED (_GL_INT_CONVERT (b, (tmin) - (a))) || (a) < (tmin))		\
+          && (b) < (tmin) - (a))							\
+       : (b) <= -1 - (a))								\
+      || ((_GL_EXPR_SIGNED (_GL_INT_CONVERT (a, b)) || (tmax) < (b))			\
+          && (tmax) < (a) + (b)))							\
+   : (tmax) < (b) || (tmax) - (b) < (a))
+#define _GL_INT_SUBTRACT_RANGE_OVERFLOW(a, b, tmin, tmax)				\
+  (((a) < 0) == ((b) < 0)								\
+   ? ((a) < (b)										\
+      ? !(tmin) || -1 - (tmin) < (b) - (a) - 1						\
+      : (tmax) < (a) - (b))								\
+   : (a) < 0										\
+   ? ((!_GL_EXPR_SIGNED (_GL_INT_CONVERT ((a) - (tmin), b)) && (a) - (tmin) < 0)	\
+      || (a) - (tmin) < (b))								\
+   : ((! (_GL_EXPR_SIGNED (_GL_INT_CONVERT (tmax, b))					\
+          && _GL_EXPR_SIGNED (_GL_INT_CONVERT ((tmax) + (b), a)))			\
+       && (tmax) <= -1 - (b))								\
+      || (tmax) + (b) < (a)))
+#define _GL_INT_MULTIPLY_RANGE_OVERFLOW(a, b, tmin, tmax)				\
+  ((b) < 0										\
+   ? ((a) < 0										\
+      ? (_GL_EXPR_SIGNED (_GL_INT_CONVERT (tmax, b))					\
+         ? (a) < (tmax) / (b)								\
+         : ((_GL_INT_NEGATE_OVERFLOW (b)						\
+             ? _GL_INT_CONVERT (b, tmax) >> (_GL_TYPE_WIDTH (+ (b)) - 1)		\
+             : (tmax) / -(b))								\
+            <= -1 - (a)))								\
+      : _GL_INT_NEGATE_OVERFLOW (_GL_INT_CONVERT (b, tmin)) && (b) == -1		\
+      ? (_GL_EXPR_SIGNED (a)								\
+         ? 0 < (a) + (tmin)								\
+         : 0 < (a) && -1 - (tmin) < (a) - 1)						\
+      : (tmin) / (b) < (a))								\
+   : (b) == 0										\
+   ? 0											\
+   : ((a) < 0										\
+      ? (_GL_INT_NEGATE_OVERFLOW (_GL_INT_CONVERT (a, tmin)) && (a) == -1		\
+         ? (_GL_EXPR_SIGNED (b) ? 0 < (b) + (tmin) : -1 - (tmin) < (b) - 1)		\
+         : (tmin) / (a) < (b))								\
+      : (tmax) / (b) < (a)))
+
+#define _GL_INT_OP_WRAPV(a, b, r, op, overflow)						\
+  (_Generic										\
+   (*(r),										\
+    signed char:									\
+    _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned int,				\
+		     signed char, SCHAR_MIN, SCHAR_MAX),				\
+    unsigned char:									\
+    _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned int,				\
+		     unsigned char, 0, UCHAR_MAX),					\
+    short int:										\
+    _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned int,				\
+		     short int, SHRT_MIN, SHRT_MAX),					\
+    unsigned short int:									\
+    _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned int,				\
+		     unsigned short int, 0, USHRT_MAX),					\
+    int:										\
+    _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned int,				\
+		     int, INT_MIN, INT_MAX),						\
+    unsigned int:									\
+    _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned int,				\
+		     unsigned int, 0, UINT_MAX),					\
+    long int:										\
+    _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned long int,				\
+		     long int, LONG_MIN, LONG_MAX),					\
+    unsigned long int:									\
+    _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned long int,				\
+		     unsigned long int, 0, ULONG_MAX),					\
+    long long int:									\
+    _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned long long int,			\
+		     long long int, LLONG_MIN, LLONG_MAX),				\
+    unsigned long long int:								\
+    _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned long long int,			\
+		     unsigned long long int, 0, ULLONG_MAX)))
+
+#define _GL_INT_ADD_WRAPV(a, b, r)							\
+  _GL_INT_OP_WRAPV (a, b, r, +, _GL_INT_ADD_RANGE_OVERFLOW)
+#define _GL_INT_SUBTRACT_WRAPV(a, b, r)							\
+  _GL_INT_OP_WRAPV (a, b, r, -, _GL_INT_SUBTRACT_RANGE_OVERFLOW)
+#define _GL_INT_MULTIPLY_WRAPV(a, b, r)							\
+  _GL_INT_OP_WRAPV (a, b, r, *, _GL_INT_MULTIPLY_RANGE_OVERFLOW)
+
+#define IntAddWrapv(a, b, r) _GL_INT_ADD_WRAPV (a, b, r)
+#define IntSubtractWrapv(a, b, r) _GL_INT_SUBTRACT_WRAPV (a, b, r)
+#define IntMultiplyWrapv(a, b, r) _GL_INT_MULTIPLY_WRAPV (a, b, r)
+
+#endif
+
+#ifndef Popcount
+#define NeedPortPopcount
+
+extern int PortPopcount (unsigned long long int);
+
+#define Popcount(number)	(PortPopcount (number))
+
+#endif