From 32164fc1e00e7658415bc9595205812794d8a0c4 Mon Sep 17 00:00:00 2001
From: Mahdi Sarikhani <mahdisarikhani@outlook.com>
Date: Mon, 23 Aug 2021 23:26:20 +0430
Subject: [PATCH 1/2] Add approximate counting algorithm in C

---
 .../approximate_counting.md                   |  2 +
 .../code/c/approximate_counting.c             | 82 +++++++++++++++++++
 2 files changed, 84 insertions(+)
 create mode 100644 contents/approximate_counting/code/c/approximate_counting.c

diff --git a/contents/approximate_counting/approximate_counting.md b/contents/approximate_counting/approximate_counting.md
index d254b99a2..fe148dcf7 100644
--- a/contents/approximate_counting/approximate_counting.md
+++ b/contents/approximate_counting/approximate_counting.md
@@ -360,6 +360,8 @@ As we do not have any objects to count, we will instead simulate the counting wi
 {% method %}
 {% sample lang="jl" %}
 [import, lang:"julia"](code/julia/approximate_counting.jl)
+{% sample lang="c" %}
+[import, lang:"c"](code/c/approximate_counting.c)
 {% endmethod %}
 
 ### Bibliography
diff --git a/contents/approximate_counting/code/c/approximate_counting.c b/contents/approximate_counting/code/c/approximate_counting.c
new file mode 100644
index 000000000..f6aff0d3d
--- /dev/null
+++ b/contents/approximate_counting/code/c/approximate_counting.c
@@ -0,0 +1,82 @@
+#include <assert.h>
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+// This function returns a pseudo-random number between 0 and 1
+double drand()
+{
+    return (double)rand() / RAND_MAX;
+}
+
+// This function takes
+//  - v: value in register
+//  - a: a scaling value for the logarithm based on Morris's paper
+// It returns the approximate count
+double n(double v, double a)
+{
+    return a * (pow(1 + 1 / a, v) - 1);
+}
+
+// This function takes
+//  - v: value in register
+//  - a: a scaling value for the logarithm based on Morris's paper
+// It returns a new value for v
+double increment(double v, double a)
+{
+    // delta is the probability of incrementing our counter
+    double delta = 1 / (n(v + 1, a) - n(v, a));
+
+    if (drand() <= delta) {
+        return v + 1;
+    }
+    return v;
+}
+
+// This function simulates counting and takes
+//  - n_items: number of items to count and loop over
+//  - a: a scaling value for the logarithm based on Morris's paper
+// It returns n(v, a), the approximate count
+double approximate_count(size_t n_items, double a)
+{
+    int v = 0;
+    for (size_t i = 0; i < n_items; ++i) {
+        v = increment(v, a);
+    }
+
+    return n(v, a);
+}
+
+// This function takes
+//  - n_trials: the number of counting trials
+//  - n_items: the number off items to count
+//  - a: a scaling value for the logarithm based on Morris's paper
+//  - threshold: the maximum percent error allowed
+// It terminates the program on failure
+void test_approximation_count(size_t n_trials, size_t n_items, double a,
+                              double threshold)
+{
+    double sum = 0.0;
+    for (size_t i = 0; i < n_trials; ++i) {
+        sum += approximate_count(n_items, a);
+    }
+    double avg = sum / n_trials;
+
+    assert(fabs((avg - n_items) / n_items) < threshold);
+}
+
+int main()
+{
+    srand(time(NULL));
+
+    printf("Counting Tests, 100 trials\n");
+    printf("testing 1000, a = 30, 1%% error\n");
+    test_approximation_count(100, 1000, 30, 0.1);
+    printf("testing 12345, a = 10, 1%% error\n");
+    test_approximation_count(100, 12345, 10, 0.1);
+    printf("testing 222222, a = 0.5, 10%% error\n");
+    test_approximation_count(100, 222222, 0.5, 0.1);
+
+    return 0;
+}

From 256bf77aead230be8f72ff40faea8a03273ea05b Mon Sep 17 00:00:00 2001
From: Mahdi Sarikhani <24981501+mahdisarikhani@users.noreply.github.com>
Date: Thu, 26 Aug 2021 04:11:16 +0430
Subject: [PATCH 2/2] Fix typo

Co-authored-by: stormofice <58337328+stormofice@users.noreply.github.com>
---
 contents/approximate_counting/code/c/approximate_counting.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/contents/approximate_counting/code/c/approximate_counting.c b/contents/approximate_counting/code/c/approximate_counting.c
index f6aff0d3d..ded7a518e 100644
--- a/contents/approximate_counting/code/c/approximate_counting.c
+++ b/contents/approximate_counting/code/c/approximate_counting.c
@@ -76,7 +76,7 @@ int main()
     printf("testing 12345, a = 10, 1%% error\n");
     test_approximation_count(100, 12345, 10, 0.1);
     printf("testing 222222, a = 0.5, 10%% error\n");
-    test_approximation_count(100, 222222, 0.5, 0.1);
+    test_approximation_count(100, 222222, 0.5, 0.2);
 
     return 0;
 }