Improve timer

Author: WilhelmWiens

src/timer.h

@@ -1,5 +1,77 @@
 #pragma once
 
+// #define USE_TSC
+
+#ifdef USE_TSC
+
+#if defined(__i386__) || defined(__x86_64__)
+
+#if defined(__GNUC__)
+#include <cpuid.h>
+#include <x86intrin.h>
+#define _ReadWriteBarrier __sync_synchronize
+#else
+#include <intrin.h>
+#endif
+
+class Timer {
+public:
+    Timer() : start_(), end_() {
+
+#if defined(__GNUC__)
+        unsigned int eax, ebx, ecx, edx;
+        if (!__get_cpuid(0x15, &eax, &ebx, &ecx, &edx) || eax == 0 || ebx == 0) {
+            // Fallback to 2.5 GHz if CPUID leaf 0x15 is not supported
+            tsc_frequency_ = 2500000000ULL;
+        } else {
+            tsc_frequency_ = (uint64_t)ecx * ebx / eax;
+        }
+#else
+        int info[4];
+        __cpuidex(info, 0x15, 0);
+        if (info[0] == 0 || info[1] == 0) {
+            // Fallback to 2.5 GHz if CPUID leaf 0x15 is not supported
+            tsc_frequency_ = 2500000000ULL;
+        } else {
+            tsc_frequency_ = (uint64_t)info[2] * info[1] / info[0];
+        }
+#endif
+    }
+
+    void Start() {
+        int info[4];
+
+        _ReadWriteBarrier();
+        __cpuidex(info, 0, 0);
+        start_ = __rdtsc();
+        _ReadWriteBarrier();
+    }
+
+    void Stop() {
+        int info[4];
+        unsigned int aux;
+        _ReadWriteBarrier();
+        end_ = __rdtscp(&aux);
+        __cpuidex(info, 0, 0);
+        _ReadWriteBarrier();
+    }
+
+    double GetElapsedMilliseconds() {
+        return (end_ - start_) * 1000.0 / tsc_frequency_;
+    }
+
+private:
+    uint64_t start_;
+    uint64_t end_;
+    uint64_t tsc_frequency_;
+};
+
+#else
+#error "TSC timer is only supported on x86/x86_64 architectures"
+#endif
+
+#else // USE_TSC
+
 #ifdef _WIN32
 
 #define WIN32_LEAN_AND_MEAN
@@ -33,6 +105,33 @@ class Timer {
 #undef min
 #undef max
 
+#elif defined(__linux__)
+
+#include <time.h>
+
+class Timer {
+public:
+    Timer() : start_(), end_() {
+    }
+
+    void Start() {
+        clock_gettime(CLOCK_MONOTONIC_RAW, &start_);
+    }
+
+    void Stop() {
+        clock_gettime(CLOCK_MONOTONIC_RAW, &end_);
+    }
+
+    double GetElapsedMilliseconds() {
+        return (end_.tv_sec - start_.tv_sec) * 1000.0
+            + (end_.tv_nsec - start_.tv_nsec) / 1000000.0;
+    }
+
+private:
+  struct timespec start_;
+  struct timespec end_;
+};
+
 #else
 
 #include <sys/time.h>
@@ -61,3 +160,4 @@ class Timer {
 };
 
 #endif
+#endif // USE_TSC