prog_util: use QueryPerformanceCounter() on Windows

QueryPerformanceCounter() is much more accurate than
GetSystemTimeAsFileTime().

Also avoid converting into a specific time unit until the results need
to be displayed.  This is more efficient and avoids losing precision.

programs/benchmark.c

@@ -352,26 +352,26 @@ do_benchmark(struct file_stream *in, void *original_buf, void *compressed_buf,
 		total_uncompressed_size += original_size;
 
 		/* Compress the chunk of data. */
-		start_time = current_time();
+		start_time = timer_ticks();
 		compressed_size = do_compress(compressor,
 					      original_buf,
 					      original_size,
 					      compressed_buf,
 					      original_size - 1);
-		total_compress_time += current_time() - start_time;
+		total_compress_time += timer_ticks() - start_time;
 
 		if (compressed_size) {
 			/* Successfully compressed the chunk of data. */
 
 			/* Decompress the data we just compressed and compare
 			 * the result with the original. */
-			start_time = current_time();
+			start_time = timer_ticks();
 			result = do_decompress(decompressor,
 					       compressed_buf,
 					       compressed_size,
 					       decompressed_buf,
 					       original_size);
-			total_decompress_time += current_time() - start_time;
+			total_decompress_time += timer_ticks() - start_time;
 
 			if (!result) {
 				msg("%"TS": failed to decompress data",
@@ -414,11 +414,11 @@ do_benchmark(struct file_stream *in, void *original_buf, void *compressed_buf,
 	       (unsigned int)(total_compressed_size * 100000 /
 				total_uncompressed_size % 1000));
 	printf("\tCompression time: %"PRIu64" ms (%"PRIu64" MB/s)\n",
-	       total_compress_time / 1000000,
-	       1000 * total_uncompressed_size / total_compress_time);
+	       timer_ticks_to_ms(total_compress_time),
+	       timer_MB_per_s(total_uncompressed_size, total_compress_time));
 	printf("\tDecompression time: %"PRIu64" ms (%"PRIu64" MB/s)\n",
-	       total_decompress_time / 1000000,
-	       1000 * total_uncompressed_size / total_decompress_time);
+	       timer_ticks_to_ms(total_decompress_time),
+	       timer_MB_per_s(total_uncompressed_size, total_decompress_time));
 
 	return 0;
 }

programs/checksum.c

@@ -79,9 +79,9 @@ checksum_stream(struct file_stream *in, cksum_fn_t cksum, u32 *sum,
 			break;
 
 		size += ret;
-		start_time = current_time();
+		start_time = timer_ticks();
 		*sum = cksum(*sum, buf, ret);
-		elapsed += current_time() - start_time;
+		elapsed += timer_ticks() - start_time;
 	}
 
 	if (elapsed == 0)
@@ -178,8 +178,8 @@ tmain(int argc, tchar *argv[])
 			if (do_timing) {
 				printf("%08"PRIx32"\t%"TS"\t"
 				       "%"PRIu64" ms\t%"PRIu64" MB/s\n",
-				       sum, in.name, elapsed / 1000000,
-				       1000 * size / elapsed);
+				       sum, in.name, timer_ticks_to_ms(elapsed),
+				       timer_MB_per_s(size, elapsed));
 			} else {
 				printf("%08"PRIx32"\t%"TS"\t\n", sum, in.name);
 			}

programs/prog_util.c

@@ -102,16 +102,16 @@ xmalloc(size_t size)
 }
 
 /*
- * Retrieve the current time in nanoseconds since a start time which is fixed
- * for the duration of program execution but is otherwise unspecified
+ * Return the number of timer ticks that have elapsed since some unspecified
+ * point fixed at the start of program execution
  */
 u64
-current_time(void)
+timer_ticks(void)
 {
 #ifdef _WIN32
-	FILETIME ft;
-	GetSystemTimeAsFileTime(&ft);
-	return 100 * (((u64)ft.dwHighDateTime << 32) | ft.dwLowDateTime);
+	LARGE_INTEGER count;
+	QueryPerformanceCounter(&count);
+	return count.QuadPart;
 #elif defined(HAVE_CLOCK_GETTIME)
 	struct timespec ts;
 	clock_gettime(CLOCK_MONOTONIC, &ts);
@@ -119,10 +119,43 @@ current_time(void)
 #else
 	struct timeval tv;
 	gettimeofday(&tv, NULL);
-	return (1000000000 * (u64)tv.tv_sec) + (1000 * (u64)tv.tv_usec);
+	return (1000000 * (u64)tv.tv_sec) + tv.tv_usec;
 #endif
 }
 
+/*
+ * Return the number of timer ticks per second
+ */
+static u64
+timer_frequency(void)
+{
+#ifdef _WIN32
+	LARGE_INTEGER freq;
+	QueryPerformanceFrequency(&freq);
+	return freq.QuadPart;
+#elif defined(HAVE_CLOCK_GETTIME)
+	return 1000000000;
+#else
+	return 1000000;
+#endif
+}
+
+/*
+ * Convert a number of elapsed timer ticks to milliseconds
+ */
+u64 timer_ticks_to_ms(u64 ticks)
+{
+	return ticks * 1000 / timer_frequency();
+}
+
+/*
+ * Convert a byte count and a number of elapsed timer ticks to MB/s
+ */
+u64 timer_MB_per_s(u64 bytes, u64 ticks)
+{
+	return bytes * timer_frequency() / ticks / 1000000;
+}
+
 /*
  * Retrieve a pointer to the filename component of the specified path.
  *

programs/prog_util.h

@@ -120,7 +120,9 @@ extern void _printf(1, 2) msg_errno(const char *fmt, ...);
 
 extern void *xmalloc(size_t size);
 
-extern u64 current_time(void);
+extern u64 timer_ticks(void);
+extern u64 timer_ticks_to_ms(u64 ticks);
+extern u64 timer_MB_per_s(u64 bytes, u64 ticks);
 
 extern const tchar *get_filename(const tchar *path);