centralized performance resources

ocw/1/matrix-multiply/fasttime.h

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+/**
+ * Copyright (c) 2014 MIT License by 6.172 Staff
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ **/
+
+#ifndef INCLUDED_FASTTIME_DOT_H
+#define INCLUDED_FASTTIME_DOT_H
+
+#include <assert.h>
+
+#ifdef __MACH__
+#include <mach/mach_time.h>  // mach_absolute_time
+
+typedef uint64_t fasttime_t;
+
+
+// Return the current time.
+static inline fasttime_t gettime(void) {
+  return mach_absolute_time();
+}
+
+// Return the time different between the start and the end, as a float
+// in units of seconds.  This function does not need to be fast.
+// Implementation notes: See
+// https://developer.apple.com/library/mac/qa/qa1398/_index.html
+static inline double tdiff(fasttime_t start, fasttime_t end) {
+  static mach_timebase_info_data_t timebase;
+  int r = mach_timebase_info(&timebase);
+  assert(r == 0);
+  fasttime_t elapsed = end-start;
+  double ns = (double)elapsed * timebase.numer / timebase.denom;
+  return ns*1e-9;
+}
+
+static inline unsigned int random_seed_from_clock(void) {
+  fasttime_t now = gettime();
+  return (now & 0xFFFFFFFF) + (now>>32);
+}
+
+#else  // LINUX
+
+// We need _POSIX_C_SOURCE to pick up 'struct timespec' and clock_gettime.
+// #define _POSIX_C_SOURCE 200809L
+
+#include <time.h>
+
+typedef struct timespec fasttime_t;
+
+// Return the current time.
+static inline fasttime_t gettime(void) {
+  struct timespec s;
+#ifdef NDEBUG
+  clock_gettime(CLOCK_MONOTONIC, &s);
+#else
+  int r = clock_gettime(CLOCK_MONOTONIC, &s);
+  assert(r == 0);
+#endif
+  return s;
+}
+
+// Return the time different between the start and the end, as a float
+// in units of seconds.  This function does not need to be fast.
+static inline double tdiff(fasttime_t start, fasttime_t end) {
+  return end.tv_sec - start.tv_sec + 1e-9*(end.tv_nsec - start.tv_nsec);
+}
+
+static inline unsigned int random_seed_from_clock(void) {
+  fasttime_t now = gettime();
+  return now.tv_sec + now.tv_nsec;
+}
+
+// Poison these symbols to help find portability problems.
+int clock_gettime(clockid_t, struct timespec *) __attribute__((deprecated));
+time_t time(time_t *) __attribute__((deprecated));
+
+#endif  // LINUX
+
+#endif  // INCLUDED_FASTTIME_DOT_H