From 0b3f3dff6087a104a0e3bc02019e8f37b4a1158d Mon Sep 17 00:00:00 2001
From: Alex Beregszaszi <alex@rtfs.hu>
Date: Tue, 27 Apr 2021 20:44:09 +0100
Subject: [PATCH] Add ramanujan's pi approximation as a semantic test

---
 .../externalContracts/ramanujan_pi.sol        | 44 +++++++++++++++++++
 1 file changed, 44 insertions(+)
 create mode 100644 test/libsolidity/semanticTests/externalContracts/ramanujan_pi.sol

diff --git a/test/libsolidity/semanticTests/externalContracts/ramanujan_pi.sol b/test/libsolidity/semanticTests/externalContracts/ramanujan_pi.sol
new file mode 100644
index 000000000..b280cfa33
--- /dev/null
+++ b/test/libsolidity/semanticTests/externalContracts/ramanujan_pi.sol
@@ -0,0 +1,44 @@
+==== ExternalSource: _prbmath/PRBMathCommon.sol ====
+==== ExternalSource: _prbmath/PRBMathSD59x18.sol ====
+==== Source: ramanujan_pi.sol ====
+import "_prbmath/PRBMathSD59x18.sol";
+
+// The goal of this test file is to implement Ramanujan's pi approximation using various libraries.
+
+function factorial(uint n) pure returns (uint ret) {
+    ret = 1;
+    for (; n > 1; --n)
+        ret *= n;
+}
+
+contract test {
+    using PRBMathSD59x18 for int256;
+
+    function prb_scale(uint n) internal pure returns (int256 ret) {
+        // Scale to SD59x18
+        ret = int256(n * 10e17);
+    }
+
+    // This dumb implementation of Ramanujan series calculates 1/pi
+    function prb_pi() external pure returns (int256 ret) {
+        uint n = 6; // More than 6 iterations results in failure
+        for (uint k = 0; k < n; k++) {
+            int256 a = prb_scale(factorial(4 * k)).div(prb_scale(factorial(k)).pow(4));
+            int256 b = (prb_scale(25390).mul(prb_scale(k)) + prb_scale(1103)).div(prb_scale(396).pow(4 * k));
+            ret += a.mul(b);
+        }
+        ret = ret.mul(prb_scale(2).sqrt().mul(prb_scale(2)).div(prb_scale(99).pow(2)));
+        ret = prb_scale(1).div(ret);
+    }
+}
+// ====
+// compileViaYul: also
+// ----
+// constructor()
+// gas irOptimized: 590192
+// gas legacy: 733634
+// gas legacyOptimized: 498033
+// prb_pi() -> 3141592656369545286
+// gas irOptimized: 66098
+// gas legacy: 98903
+// gas legacyOptimized: 75735