Add more precise clocks

Author: Raimo33

CMakeLists.txt

@@ -30,6 +30,8 @@ set(${PROJECT_NAME}_LIB_VERSION_AGE 0)
 #=============================
 set(CMAKE_C_STANDARD 90)
 set(CMAKE_C_EXTENSIONS OFF)
+# Enable POSIX features while maintaining ISO C compliance
+add_compile_definitions(_POSIX_C_SOURCE=200112L) #needed for `clock_gettime()` in bench.c
 
 #=============================
 # Configurable options

README.md

@@ -159,6 +159,8 @@ Benchmark
 ------------
 If configured with `--enable-benchmark` (which is the default), binaries for benchmarking the libsecp256k1 functions will be present in the root directory after the build.
 
+For an accurate benchmark, it is strongly recommended to pin the process to a dedicated CPU core and to disable CPU frequency scaling.
+
 To print the benchmark result to the command line:
 
     $ ./bench_name

src/bench.h

@@ -7,30 +7,63 @@
 #ifndef SECP256K1_BENCH_H
 #define SECP256K1_BENCH_H
 
+#if defined(_WIN32)
+# include <windows.h>
+#else
+# include <time.h>
+# include <sys/time.h>
+#endif
+
 #include <stdlib.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <string.h>
 
-#if (defined(_MSC_VER) && _MSC_VER >= 1900)
-#  include <time.h>
-#else
-#  include <sys/time.h>
-#endif
+static int64_t gettime_us(void) {
+#if defined(_WIN32)
+    FILETIME creation, exit, kernel, user;
 
-static int64_t gettime_i64(void) {
-#if (defined(_MSC_VER) && _MSC_VER >= 1900)
-    /* C11 way to get wallclock time */
-    struct timespec tv;
-    if (!timespec_get(&tv, TIME_UTC)) {
-        fputs("timespec_get failed!", stderr);
-        exit(EXIT_FAILURE);
+    if (GetProcessTimes(GetCurrentProcess(), &creation, &exit, &kernel, &user) == 0) {
+        return 0;
     }
-    return (int64_t)tv.tv_nsec / 1000 + (int64_t)tv.tv_sec * 1000000LL;
-#else
+
+    ULARGE_INTEGER k, u;
+    k.LowPart = kernel.dwLowDateTime;
+    k.HighPart = kernel.dwHighDateTime;
+    u.LowPart = user.dwLowDateTime;
+    u.HighPart = user.dwHighDateTime;
+
+    return (int64_t)((k.QuadPart + u.QuadPart) / 10);
+#else /* POSIX */
+
+# if defined(CLOCK_PROCESS_CPUTIME_ID)
+    /* in theory, CLOCK_PROCESS_CPUTIME_ID is only useful if the process is locked to a core. see https://linux.die.net/man/3/clock_gettime */
+    struct timespec ts;
+    if (clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &ts) != 0) {
+        return 0;
+    }
+    return (int64_t)ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
+# elif defined(CLOCK_MONOTONIC)
+    /* WARN: timer is influenced by environvment (OS, scheduling, interrupts...) */
+    struct timespec ts;
+    if (clock_gettime(CLOCK_MONOTONIC, &ts) != 0) {
+        return 0;
+    }
+    return (int64_t)ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
+# elif defined(CLOCK_REALTIME)
+    /* WARN: timer is influenced by environvment (OS, scheduling, interrupts...) */
+    struct timespec ts;
+    if (clock_gettime(CLOCK_REALTIME, &ts) != 0) {
+        return 0;
+    }
+    return (int64_t)ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
+# else
+    /* WARN: timer is influenced by environvment (OS, scheduling, interrupts...) */
     struct timeval tv;
-    gettimeofday(&tv, NULL);
-    return (int64_t)tv.tv_usec + (int64_t)tv.tv_sec * 1000000LL;
+    gettimeofday((struct timeval*)&tv, NULL);
+    return (int64_t)tv.tv_sec * 1000000 + tv.tv_usec;
+# endif
+
 #endif
 }
 
@@ -44,9 +77,9 @@ static void run_benchmark(char *name, void (*benchmark)(void*, int), void (*setu
         if (setup != NULL) {
             setup(data);
         }
-        begin = gettime_i64();
+        begin = gettime_us();
         benchmark(data, iter);
-        total = gettime_i64() - begin;
+        total = gettime_us() - begin;
         if (teardown != NULL) {
             teardown(data, iter);
         }