Mail Archives: djgpp-workers/2003/02/12/22:52:57

From: sandmann AT clio DOT rice DOT edu (Charles Sandmann)
Message-Id: <>
Subject: _rdtsc proposal
To: djgpp-workers AT delorie DOT com (DJGPP developers)
Date: Wed, 12 Feb 2003 21:55:10 -0600 (CST)
X-Mailer: ELM [version 2.5 PL2]
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Reply-To: djgpp-workers AT delorie DOT com

Given the FAQ nature of rdtsc; given the potential to use this in libc;
for your amusement and comments.  Patterned after farptr.h.  When
used inline for timing generates the single assembly instruction with
no additional overhead (cool for timing small C sections).  If OK,
also will add makefile entry and docs.  Yes I know it can kill
some CPUs - that will be in the docs with an example how to work
around it.  (For those that don't know, the construct below will
inline with appropriate optimization, and will call libc module 
if compiled with no optimization).

--- time.bak	Tue Feb  4 20:46:08 2003
+++ time.h	Wed Feb 12 21:43:38 2003
@@ -100,6 +100,16 @@ int		settimeofday(struct timeval *_tp, .
 void		tzsetwall(void);
 uclock_t	uclock(void);
+unsigned long long _rdtsc(void);
+extern __inline__ unsigned long long
+  unsigned long long result;
+  __asm__ __volatile__ ("rdtsc" : "=A"(result) );
+  return result;
 #endif /* !_POSIX_SOURCE */
 #endif /* !__STRICT_ANSI__ */

--- src/libc/pc_hw/timer/rdtsc.c

/* Copyright (C) 2003 DJ Delorie, see COPYING.DJ for details */
#define extern
#define __inline__
#include <time.h>

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