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diff --git a/src/asm/matha.s b/src/asm/matha.s
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+/*
+===========================================================================
+Copyright (C) 1999-2005 Id Software, Inc.
+Copyright (C) 2015-2019 GrangerHub
+
+This file is part of Tremulous.
+
+Tremulous 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.
+
+Tremulous 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 Tremulous; if not, see <https://www.gnu.org/licenses/>
+
+===========================================================================
+*/
+//
+// math.s
+// x86 assembly-language math routines.
+
+#include "qasm.h"
+
+
+#if	id386
+
+	.text
+
+// TODO: rounding needed?
+// stack parameter offset
+#define	val	4
+
+.globl C(Invert24To16)
+C(Invert24To16):
+
+	movl	val(%esp),%ecx
+	movl	$0x100,%edx		// 0x10000000000 as dividend
+	cmpl	%edx,%ecx
+	jle		LOutOfRange
+
+	subl	%eax,%eax
+	divl	%ecx
+
+	ret
+
+LOutOfRange:
+	movl	$0xFFFFFFFF,%eax
+	ret
+
+#endif	// id386