The original Quake 2 sources as originally released under the GPL license on December 21, 2001.

client/x86.c

@@ -0,0 +1,95 @@
+/*
+Copyright (C) 1997-2001 Id Software, Inc.
+
+This program 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 2
+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 General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
+
+*/
+#include <stdlib.h>
+#include "client.h"
+
+#if id386
+
+static unsigned long bias;
+static unsigned long *histogram;
+static unsigned long start, range;
+static unsigned long bias;
+
+__declspec( naked ) void x86_TimerStart( void )
+{
+	__asm _emit 0fh
+	__asm _emit 31h
+	__asm mov  start, eax
+	__asm ret
+}
+
+__declspec( naked ) void x86_TimerStop( void )
+{
+	__asm push edi
+	__asm mov edi, histogram
+	__asm _emit 0fh
+	__asm _emit 31h
+	__asm sub eax, start
+	__asm sub eax, bias
+	__asm js discard
+	__asm cmp eax, range
+	__asm jge  discard
+	__asm lea edi, [edi + eax*4]
+	__asm inc dword ptr [edi]
+discard:
+	__asm pop edi
+	__asm ret
+}
+
+#pragma warning( disable: 4035 )
+static __declspec( naked ) unsigned long x86_TimerStopBias( void )
+{
+	__asm push edi
+	__asm mov edi, histogram
+	__asm _emit 0fh
+	__asm _emit 31h
+	__asm sub eax, start
+	__asm pop edi
+	__asm ret
+}
+#pragma warning( default:4035 )
+
+void x86_TimerInit( unsigned long smallest, unsigned length )
+{
+	int i;
+	unsigned long biastable[100];
+
+	range = length;
+	bias = 10000;
+
+	for ( i = 0; i < 100; i++ )
+	{
+		x86_TimerStart();
+		biastable[i] = x86_TimerStopBias();
+
+		if ( bias > biastable[i] )
+			bias = biastable[i];
+	}
+
+	bias += smallest;
+	histogram = Z_Malloc( range * sizeof( unsigned long ) );
+}
+
+unsigned long *x86_TimerGetHistogram( void )
+{
+	return histogram;
+}
+
+#endif