12 files changed, 269 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..1710c5a
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+sort-benchmark/*/sort
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..17b7043
--- /dev/null
+++ b/README.md
@@ -0,0 +1,19 @@
+# Taming C++
+
+Experiments with C++ and comparisons with C.
+
+## sort-benchmark
+
+Inspired by [Bert's post](https://berthub.eu/articles/posts/c++-1).
+
+Sorting an array of integers is a simple task, so C and C++ should perform
+similarly, right? Wrong!
+
+```
+C time for 100000000 numbers: 9.886314s
+C++ time for 100000000 numbers: 4.92299s
+C++ time for 100000000 numbers (parallel): 0.495435s
+```
+
+A similar benchmark is provided for sorting an arrays of pairs in a
+non-standard way.
diff --git a/sort-benchmark/integers/Makefile b/sort-benchmark/integers/Makefile
new file mode 100644
index 0000000..56a37ee
--- /dev/null
+++ b/sort-benchmark/integers/Makefile
@@ -0,0 +1,20 @@
+CC = gcc
+CPP = g++
+OPT = -O3
+VAR = -DARRAYSIZE=100000000
+
+all: sort_c sort_cpp sort_parallel_cpp
+
+sort_c:
+        ${CC} ${OPT} ${VAR} -std=c11 -o sort sort.c
+        ./sort
+
+sort_cpp:
+        ${CPP} ${OPT} ${VAR} -std=c++20 -o sort sort.cpp 
+        ./sort
+
+sort_parallel_cpp:
+        ${CPP} ${OPT} ${VAR} -std=c++20 -o sort sort_parallel.cpp -ltbb
+        ./sort
+
+.PHONY: sort_c sort_cpp sort_parallel_cpp
diff --git a/sort-benchmark/integers/notes.txt b/sort-benchmark/integers/notes.txt
new file mode 100644
index 0000000..7984803
--- /dev/null
+++ b/sort-benchmark/integers/notes.txt
@@ -0,0 +1,11 @@
+- Getting the parallel version to work was a pain. Two major gotchas:
+        (1) -ltbb had to be added *at the end* of the command line
+        (2) clang requires a libstdc++ option to make this work
+  of course everything was terrible to decipher with C++ compile errors
+  being the mess they are.
+- For measuring time I could also use
+        clock_t begin = clock();
+        ...
+        clock_t end = clock();
+        double time = (dobule)(end - begin) / CLOCKS_PER_SEC;
+  but it does not work with the parallel version (it meausres CPU clocks).
diff --git a/sort-benchmark/integers/sort.c b/sort-benchmark/integers/sort.c
new file mode 100644
index 0000000..2a23d9d
--- /dev/null
+++ b/sort-benchmark/integers/sort.c
@@ -0,0 +1,29 @@
+#define _POSIX_C_SOURCE 200809L /* Required to use clock_gettime */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+int a[ARRAYSIZE];
+
+int compar(const void *x, const void *y) { return *(int *)x - *(int *)y; }
+
+int main() {
+        srand(time(NULL));
+        for (int i = 0; i < ARRAYSIZE; i++) a[i] = rand() % 1000000000;
+
+        struct timespec begin;
+        clock_gettime(CLOCK_MONOTONIC, &begin);
+
+        qsort(a, ARRAYSIZE, sizeof(int), compar);
+
+        struct timespec end;
+        clock_gettime(CLOCK_MONOTONIC, &end);
+        double time = end.tv_sec - begin.tv_sec +
+                (end.tv_nsec - begin.tv_nsec) / 1000000000.0;
+
+        printf("(%d) C time for %d numbers: %lfs\n",
+                a[ARRAYSIZE/2], ARRAYSIZE, time);
+
+        return 0;
+}
diff --git a/sort-benchmark/integers/sort.cpp b/sort-benchmark/integers/sort.cpp
new file mode 100644
index 0000000..3434d7f
--- /dev/null
+++ b/sort-benchmark/integers/sort.cpp
@@ -0,0 +1,25 @@
+#include <algorithm>
+#include <cstdlib>
+#include <ctime>
+#include <iostream>
+
+int a[ARRAYSIZE];
+
+int main(void) {
+        srand(time(NULL));
+        for (auto &x : a) x = rand() % 1000000000;
+
+        struct timespec begin;
+        clock_gettime(CLOCK_MONOTONIC, &begin);
+
+        std::sort(a, a+ARRAYSIZE,
+                [](const int &x, const int &y) { return x < y; });
+
+        struct timespec end;
+        clock_gettime(CLOCK_MONOTONIC, &end);
+        double time = end.tv_sec - begin.tv_sec +
+                (end.tv_nsec - begin.tv_nsec) / 1000000000.0;
+
+        std::cout << "(" << a[ARRAYSIZE/2] << ") C++ time for " << ARRAYSIZE
+                << " numbers: " << time << "s\n";
+}
diff --git a/sort-benchmark/integers/sort_parallel.cpp b/sort-benchmark/integers/sort_parallel.cpp
new file mode 100644
index 0000000..5de4158
--- /dev/null
+++ b/sort-benchmark/integers/sort_parallel.cpp
@@ -0,0 +1,28 @@
+/* Requires Thread Building Blocks (libtbb-dev on Debian) */
+
+#include <algorithm>
+#include <cstdlib>
+#include <ctime>
+#include <execution>
+#include <iostream>
+
+int a[ARRAYSIZE];
+
+int main(void) {
+        srand(time(NULL));
+        for (auto &x : a) x = rand() % 1000000000;
+
+        struct timespec begin;
+        clock_gettime(CLOCK_MONOTONIC, &begin);
+
+        std::sort(std::execution::par, a, a+ARRAYSIZE,
+                [](const int &x, const int &y) { return x < y; });
+
+        struct timespec end;
+        clock_gettime(CLOCK_MONOTONIC, &end);
+        double time = end.tv_sec - begin.tv_sec +
+                (end.tv_nsec - begin.tv_nsec) / 1000000000.0;
+
+        std::cout << "(" << a[ARRAYSIZE/2] << ") C++ time for " << ARRAYSIZE
+                << " numbers (parallel): " << time << "s\n";
+}
diff --git a/sort-benchmark/pairs/Makefile b/sort-benchmark/pairs/Makefile
new file mode 100644
index 0000000..56a37ee
--- /dev/null
+++ b/sort-benchmark/pairs/Makefile
@@ -0,0 +1,20 @@
+CC = gcc
+CPP = g++
+OPT = -O3
+VAR = -DARRAYSIZE=100000000
+
+all: sort_c sort_cpp sort_parallel_cpp
+
+sort_c:
+        ${CC} ${OPT} ${VAR} -std=c11 -o sort sort.c
+        ./sort
+
+sort_cpp:
+        ${CPP} ${OPT} ${VAR} -std=c++20 -o sort sort.cpp 
+        ./sort
+
+sort_parallel_cpp:
+        ${CPP} ${OPT} ${VAR} -std=c++20 -o sort sort_parallel.cpp -ltbb
+        ./sort
+
+.PHONY: sort_c sort_cpp sort_parallel_cpp
diff --git a/sort-benchmark/pairs/notes.txt b/sort-benchmark/pairs/notes.txt
new file mode 100644
index 0000000..7984803
--- /dev/null
+++ b/sort-benchmark/pairs/notes.txt
@@ -0,0 +1,11 @@
+- Getting the parallel version to work was a pain. Two major gotchas:
+        (1) -ltbb had to be added *at the end* of the command line
+        (2) clang requires a libstdc++ option to make this work
+  of course everything was terrible to decipher with C++ compile errors
+  being the mess they are.
+- For measuring time I could also use
+        clock_t begin = clock();
+        ...
+        clock_t end = clock();
+        double time = (dobule)(end - begin) / CLOCKS_PER_SEC;
+  but it does not work with the parallel version (it meausres CPU clocks).
diff --git a/sort-benchmark/pairs/sort.c b/sort-benchmark/pairs/sort.c
new file mode 100644
index 0000000..826a684
--- /dev/null
+++ b/sort-benchmark/pairs/sort.c
@@ -0,0 +1,38 @@
+#define _POSIX_C_SOURCE 200809L /* Required to use clock_gettime */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+typedef struct { int a, b; } pair_t;
+pair_t a[ARRAYSIZE];
+
+int compar(const void *x, const void *y) {
+        pair_t *p = (pair_t *)x;
+        pair_t *q = (pair_t *)y;
+        int d = p->a - q->a;
+        return d > 0 ? 1 : (d < 0 ? -1 : (q->b - p->b));
+}
+
+int main() {
+        srand(time(NULL));
+        for (int i = 0; i < ARRAYSIZE; i++) {
+                a[i].a = rand() % 1000000;
+                a[i].b = rand() % 1000000;
+        }
+
+        struct timespec begin;
+        clock_gettime(CLOCK_MONOTONIC, &begin);
+
+        qsort(a, ARRAYSIZE, sizeof(pair_t), compar);
+
+        struct timespec end;
+        clock_gettime(CLOCK_MONOTONIC, &end);
+        double time = end.tv_sec - begin.tv_sec +
+                (end.tv_nsec - begin.tv_nsec) / 1000000000.0;
+
+        printf("(%d) C time for %d pairs: %lfs\n",
+                a[ARRAYSIZE/2].a, ARRAYSIZE, time);
+
+        return 0;
+}
diff --git a/sort-benchmark/pairs/sort.cpp b/sort-benchmark/pairs/sort.cpp
new file mode 100644
index 0000000..77ab5f0
--- /dev/null
+++ b/sort-benchmark/pairs/sort.cpp
@@ -0,0 +1,32 @@
+#include <algorithm>
+#include <cstdlib>
+#include <ctime>
+#include <iostream>
+
+typedef struct { int a, b; } pair_t;
+pair_t a[ARRAYSIZE];
+
+int main(void) {
+        srand(time(NULL));
+        for (auto &x : a) {
+                x.a = rand() % 1000000;
+                x.b = rand() % 1000000;
+        }
+
+        struct timespec begin;
+        clock_gettime(CLOCK_MONOTONIC, &begin);
+
+        std::sort(a, a+ARRAYSIZE,
+                [](const pair_t &x, const pair_t &y) {
+                        int d = x.a - y.a;
+                        return d < 0 || (d == 0 && x.b > y.b);
+                });
+
+        struct timespec end;
+        clock_gettime(CLOCK_MONOTONIC, &end);
+        double time = end.tv_sec - begin.tv_sec +
+                (end.tv_nsec - begin.tv_nsec) / 1000000000.0;
+
+        std::cout << "(" << a[ARRAYSIZE/2].a << ") C++ time for " << ARRAYSIZE
+                << " pairs: " << time << "s\n";
+}
diff --git a/sort-benchmark/pairs/sort_parallel.cpp b/sort-benchmark/pairs/sort_parallel.cpp
new file mode 100644
index 0000000..ef9ee05
--- /dev/null
+++ b/sort-benchmark/pairs/sort_parallel.cpp
@@ -0,0 +1,35 @@
+/* Requires Thread Building Blocks (libtbb-dev on Debian) */
+
+#include <algorithm>
+#include <cstdlib>
+#include <ctime>
+#include <execution>
+#include <iostream>
+
+typedef struct { int a, b; } pair_t;
+pair_t a[ARRAYSIZE];
+
+int main(void) {
+        srand(time(NULL));
+        for (auto &x : a) {
+                x.a = rand() % 1000000;
+                x.b = rand() % 1000000;
+        }
+
+        struct timespec begin;
+        clock_gettime(CLOCK_MONOTONIC, &begin);
+
+        std::sort(std::execution::par, a, a+ARRAYSIZE,
+                [](const pair_t &x, const pair_t &y) {
+                        int d = x.a - y.a;
+                        return d < 0 || (d == 0 && x.b > y.b);
+                });
+
+        struct timespec end;
+        clock_gettime(CLOCK_MONOTONIC, &end);
+        double time = end.tv_sec - begin.tv_sec +
+                (end.tv_nsec - begin.tv_nsec) / 1000000000.0;
+
+        std::cout << "(" << a[ARRAYSIZE/2].a << ") C++ time for " << ARRAYSIZE
+                << " pairs (parallel): " << time << "s\n";
+}