Subject: [Boost-commit] svn:boost r55644 - trunk/libs/spirit/benchmarks
From: hartmut.kaiser_at_[hidden]
Date: 2009-08-17 22:17:03
Author: hkaiser
Date: 2009-08-17 22:17:03 EDT (Mon, 17 Aug 2009)
New Revision: 55644
URL: http://svn.boost.org/trac/boost/changeset/55644
Log:
Applied more high_resolution_timer fixes provided by Edward Grace
Text files modified:
trunk/libs/spirit/benchmarks/high_resolution_timer.hpp | 59 +++++++++++++++++++++++++++++++--------
1 files changed, 47 insertions(+), 12 deletions(-)
Modified: trunk/libs/spirit/benchmarks/high_resolution_timer.hpp
==============================================================================
--- trunk/libs/spirit/benchmarks/high_resolution_timer.hpp (original)
+++ trunk/libs/spirit/benchmarks/high_resolution_timer.hpp 2009-08-17 22:17:03 EDT (Mon, 17 Aug 2009)
@@ -323,6 +323,36 @@
///////////////////////////////////////////////////////////////////////////
class high_resolution_timer
{
+ private:
+ template <typename U>
+ static inline double unsigned_diff(const U &a, const U &b)
+ {
+ if (a > b)
+ return static_cast<double>(a-b);
+ return -static_cast<double>(b-a);
+ }
+
+ // @brief Return the difference between two timeval types.
+ //
+ // @param t1 The most recent timeval.
+ // @param t0 The historical timeval.
+ //
+ // @return The difference between the two in seconds.
+ double elapsed(const timeval &t1, const timeval &t0) const
+ {
+ if (t1.tv_sec == t0.tv_sec)
+ return unsigned_diff(t1.tv_usec,t0.tv_usec) * 1e-6;
+
+ // We do it this way as the result of the difference of the
+ // microseconds can be negative if the clock is implemented so
+ // that the seconds timer increases in large steps.
+ //
+ // Naive subtraction of the unsigned types and conversion to
+ // double can wreak havoc!
+ return unsigned_diff(t1.tv_sec,t0.tv_sec) +
+ unsigned_diff(t1.tv_usec,t0.tv_usec) * 1e-6;
+ }
+
public:
high_resolution_timer()
{
@@ -368,12 +398,7 @@
timeval now;
if (gettimeofday(&now, NULL))
boost::throw_exception(std::runtime_error("Couldn't get current time"));
-
- if (now.tv_sec == start_time.tv_sec)
- return double(now.tv_usec - start_time.tv_usec) * 1e-6;
-
- return double(now.tv_usec - start_time.tv_sec) +
- (double(now.tv_usec - start_time.tv_usec) * 1e-6);
+ return elapsed(now,start_time);
}
double elapsed_max() const // return estimated maximum value for elapsed()
@@ -388,19 +413,18 @@
// by repeatedly calling the gettimeofday function. This
// is often likely to be indicative of the true
// resolution.
- timeval a, b;
+ timeval t1, t2;
double delta(0);
- if (gettimeofday(&a, NULL))
+ if (gettimeofday(&t0, NULL))
boost::throw_exception(std::runtime_error("Couldn't get resolution."));
// Spin around in a tight loop until we observe a change
// in the reported timer value.
do {
- if (gettimeofday(&b, NULL))
+ if (gettimeofday(&t1, NULL))
boost::throw_exception(std::runtime_error("Couldn't get resolution."));
- delta = double(b.tv_sec - a.tv_sec) +
- double(b.tv_usec - a.tv_usec) * 1e-6;
+ delta = elapsed(t1, t0);
} while (delta <= 0.0);
return delta;
@@ -434,6 +458,17 @@
#endif
-#endif
+#endif // HIGH_RESOLUTION_TIMER_AUG_14_2009_0425PM
+
+//
+// $Log: high_resolution_timer.hpp,v $
+// Revision 1.4 2009/08/14 15:28:10 graceej
+// * It is entirely possible for the updating clock to increment the
+// * seconds and *decrement* the microseconds field. Consequently
+// * when subtracting these unsigned microseconds fields a wrap-around
+// * error can occur. For this reason elapsed(t1, t0) is used in a
+// * similar maner to cycle.h this preserves the sign of the
+// * difference.
+//