Add stddev and a small test case for Stats

Author: Henry Qin

Makefile

@@ -41,7 +41,7 @@ $(OBJECT_DIR)/cycles_wrapper_test: $(OBJECT_DIR)/cycles_wrapper_test.o $(OBJECT_
 	$(CC) $(CFLAGS) -lstdc++ -o $@ $^
 
 $(OBJECT_DIR)/perf_wrapper_test: $(OBJECT_DIR)/perf_wrapper_test.o $(OBJECT_DIR)/libPerfUtils.a
-	$(CC) $(CFLAGS) -lstdc++ -o $@ $^
+	$(CC) $(CFLAGS) -lstdc++ -o $@ $^ -lm
 
 -include $(DEP)
 
@@ -76,9 +76,10 @@ GMOCK_DIR=../googletest/googlemock
 TEST_LIBS=-Lobj/ -lPerfUtils $(OBJECT_DIR)/libgtest.a  $(OBJECT_DIR)/libgmock.a
 INCLUDE+=-I${GTEST_DIR}/include -I${GMOCK_DIR}/include
 
-test: $(OBJECT_DIR)/UtilTest $(OBJECT_DIR)/PerfTest
+test: $(OBJECT_DIR)/UtilTest $(OBJECT_DIR)/PerfTest $(OBJECT_DIR)/StatsTest
 	$(OBJECT_DIR)/UtilTest
 	$(OBJECT_DIR)/PerfTest
+	$(OBJECT_DIR)/StatsTest
 
 $(OBJECT_DIR)/UtilTest: $(OBJECT_DIR)/UtilTest.o $(OBJECT_DIR)/libgtest.a  $(OBJECT_DIR)/libgmock.a \
 						$(OBJECT_DIR)/libPerfUtils.a
@@ -88,6 +89,10 @@ $(OBJECT_DIR)/PerfTest: $(OBJECT_DIR)/PerfTest.o $(OBJECT_DIR)/libgtest.a  $(OBJ
 						$(OBJECT_DIR)/libPerfUtils.a
 	$(CXX) $(INCLUDE) $(CXXFLAGS) $< $(GTEST_DIR)/src/gtest_main.cc $(TEST_LIBS) $(LIBS)  -o $@
 
+$(OBJECT_DIR)/StatsTest: $(OBJECT_DIR)/StatsTest.o $(OBJECT_DIR)/libgtest.a  $(OBJECT_DIR)/libgmock.a \
+						$(OBJECT_DIR)/libPerfUtils.a
+	$(CXX) $(INCLUDE) $(CXXFLAGS) $< $(GTEST_DIR)/src/gtest_main.cc $(TEST_LIBS) $(LIBS)  -o $@
+
 $(OBJECT_DIR)/libgtest.a:
 	$(CXX) -I${GTEST_DIR}/include -I${GTEST_DIR} \
         -pthread -c ${GTEST_DIR}/src/gtest-all.cc \

src/Stats.cc

@@ -39,6 +39,14 @@ computeStatistics(uint64_t* rawdata, size_t count) {
         sum += rawdata[i];
     stats.count = count;
     stats.average = sum / count;
+    stats.stddev = 0;
+    for (size_t i = 0; i < count; i++) {
+        uint64_t diff = rawdata[i] > stats.average ? rawdata[i] - stats.average
+            : stats.average - rawdata[i];
+        stats.stddev += diff * diff;
+    }
+    stats.stddev /= count;
+    stats.stddev = static_cast<uint64_t>(sqrt(stats.stddev));
     stats.min = rawdata[0];
     stats.median = rawdata[count / 2];
     stats.P10 = rawdata[static_cast<int>(static_cast<double>(count) * 0.1)];

src/StatsMinimal.h

@@ -25,6 +25,7 @@
 struct Statistics {
     size_t count;
     uint64_t average;
+    uint64_t stddev;
     uint64_t min;
     uint64_t median;
     uint64_t P10;

src/StatsTest.cc

@@ -0,0 +1,39 @@
+/* Copyright (c) 2014-2017 Stanford University
+ *
+ * Permission to use, copy, modify, and distribute this software for any purpose
+ * with or without fee is hereby granted, provided that the above copyright
+ * notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR(S) DISCLAIM ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL AUTHORS BE LIABLE FOR ANY
+ * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER
+ * RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF
+ * CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "Stats.h"
+
+#include <fcntl.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+
+TEST(StatsTest, allStats) {
+    const int numElements = 100;
+    uint64_t input[numElements];
+    for (uint64_t i = 0; i < numElements; i++)
+        input[i] = i;
+    Statistics stats = computeStatistics(input, numElements);
+    EXPECT_EQ(numElements, stats.count);
+    EXPECT_EQ(0, stats.min);
+    EXPECT_EQ(99, stats.max);
+    EXPECT_EQ(50, stats.median);
+    EXPECT_EQ(49, stats.average);
+    EXPECT_EQ(28, stats.stddev);
+}