benchmarks: add Ramanujan's formula for calculating pi

test/benchmarks/ramanujan_pi.c

@@ -0,0 +1,34 @@
+#include <math.h>
+
+#define WASM_EXPORT __attribute__((visibility("default")))
+
+static unsigned factorial(unsigned n)
+{
+    unsigned ret = 1;
+    for (unsigned i = n; i > 1; --i)
+        ret *= i;
+    return ret;
+}
+
+static double ramanujan_pi(unsigned n)
+{
+    // This dumb implementation of Ramanujan series calculates 1/pi
+    double ret = 0.0;
+    for (unsigned k = 0; k < n; k++) {
+        double a = factorial(4 * k) / pow(factorial(k), 4.0);
+        double b = (26390.0 * k + 1103.0) / pow(396.0, 4 * k);
+        ret += a * b;
+    }
+
+    // Some intentional f32 -> f64 conversion here
+    ret *= (2.0f * sqrt(2.0)) / pow(99.0f, 2.0);
+
+    // Return pi
+    return 1.0 / ret;
+}
+
+WASM_EXPORT unsigned long long ramanujan(unsigned n)
+{
+    // Display all 16 digits of double precision as a 64-bit integer
+    return ramanujan_pi(n) * 10000000000000000ULL;
+}

test/benchmarks/ramanujan_pi.inputs

@@ -0,0 +1,14 @@
+pi_10_runs
+ramanujan
+i:I
+10
+
+31415926535897932
+
+pi_30_runs
+ramanujan
+i:I
+30
+
+31415926535897932
+