From 259302b3686b6b1f3056f8bdea54c7341e15df10 Mon Sep 17 00:00:00 2001
From: "Peter J. Holzer" <hjp@hjp.at>
Date: Sat, 24 Oct 2020 01:29:41 +0200
Subject: [PATCH] Benchmark linked list in C

---
 c/Makefile      |  2 ++
 c/linked-list.c | 69 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 71 insertions(+)
 create mode 100644 c/Makefile
 create mode 100644 c/linked-list.c

diff --git a/c/Makefile b/c/Makefile
new file mode 100644
index 0000000..bed797a
--- /dev/null
+++ b/c/Makefile
@@ -0,0 +1,2 @@
+CFLAGS = -g -O9
+linked-list:
diff --git a/c/linked-list.c b/c/linked-list.c
new file mode 100644
index 0000000..2b5e984
--- /dev/null
+++ b/c/linked-list.c
@@ -0,0 +1,69 @@
+#include <inttypes.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+
+typedef struct node nodeT;
+
+struct node {
+    uint_fast64_t value;
+    nodeT *next;
+};
+
+typedef struct result {
+    size_t count;
+    double total_time;
+    double avg_time;
+    uint_fast64_t sum;
+} resultT;
+
+nodeT *build(size_t n) {
+    nodeT *first = malloc(sizeof(nodeT));
+    nodeT *last = first;
+    for (size_t i = 1; i < n; i++) {
+        nodeT *node = malloc(sizeof(nodeT));
+        node->value = i;
+        last->next = node;
+        last = node;
+    }
+    last->next = first;
+    return first;
+}
+
+resultT traverse(nodeT *p) {
+    struct timespec ts0;
+    size_t n = 0;
+    uint_fast64_t sum = 0;
+    clock_gettime(CLOCK_MONOTONIC, &ts0);
+    for (;;) {
+        for (uint_fast32_t i = 0; i < 1000000; i++) {
+            p = p->next;
+            sum += p->value;
+            n++;
+        }
+
+        struct timespec ts1;
+        clock_gettime(CLOCK_MONOTONIC, &ts1);
+        double dt = (ts1.tv_sec - ts0.tv_sec) + (ts1.tv_nsec - ts0.tv_nsec) / 1E9;
+        if (dt >= 1) {
+            resultT r;
+            r.count = n;
+            r.total_time = dt;
+            r.avg_time = dt / n;
+            r.sum = sum;
+            return r;
+        }
+    }
+}
+
+int main (void) {
+    size_t n;
+    for (n = 2; ; n *= 2) {
+        nodeT *p = build(n);
+        resultT r = traverse(p);
+        printf("%zu %zu %g %g %" PRIuFAST64 "\n",
+               n, r.count, r.total_time, r.avg_time, r.sum);
+    }
+}