From 2696740c01ba934de31cb83e3e8166f4e17dcd15 Mon Sep 17 00:00:00 2001
From: Moritz Bunkus <mo@bunkus.online>
Date: Mon, 5 Jul 2021 17:37:26 +0200
Subject: [PATCH] math: add rounding-conversion functions for rationals

---
 src/common/math_fwd.h      | 12 ++++++++++++
 tests/unit/common/math.cpp | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/src/common/math_fwd.h b/src/common/math_fwd.h
index 3cf73b8e8..c69fb81a7 100644
--- a/src/common/math_fwd.h
+++ b/src/common/math_fwd.h
@@ -47,6 +47,18 @@ to_uint(mtx_mp_rational_t const &value) {
   return static_cast<uint64_t>(static_cast<boost::multiprecision::uint128_t>(value));
 }
 
+// Additional conversions that round to the nearest integer away from 0.
+inline int64_t
+to_int_rounded(mtx_mp_rational_t const &value) {
+  auto shift = value >= 0 ? 5 : -5;
+  return static_cast<int64_t>((static_cast<boost::multiprecision::int128_t>(value * 10 + shift)) / 10);
+}
+
+inline uint64_t
+to_uint_rounded(mtx_mp_rational_t const &value) {
+  return static_cast<uint64_t>((static_cast<boost::multiprecision::uint128_t>(value * 10 + 5)) / 10);
+}
+
 namespace math {
 }
 
diff --git a/tests/unit/common/math.cpp b/tests/unit/common/math.cpp
index 3afab332d..6b51dd794 100644
--- a/tests/unit/common/math.cpp
+++ b/tests/unit/common/math.cpp
@@ -74,4 +74,38 @@ TEST(Math, ClampValueTo) {
   EXPECT_EQ((mtx_mp_rational_t{65'535,      1}), mtx::math::clamp_values_to({999'999'999,       1}, 65535));
 }
 
+TEST(Math, ToIntTruncating) {
+  EXPECT_EQ(mtx::to_int(mtx::rational(-0, 3)), -0);
+  EXPECT_EQ(mtx::to_int(mtx::rational(-1, 3)), -0);
+  EXPECT_EQ(mtx::to_int(mtx::rational(-2, 3)), -0);
+  EXPECT_EQ(mtx::to_int(mtx::rational(-3, 3)), -1);
+
+  EXPECT_EQ(mtx::to_int(mtx::rational(0, 3)), 0);
+  EXPECT_EQ(mtx::to_int(mtx::rational(1, 3)), 0);
+  EXPECT_EQ(mtx::to_int(mtx::rational(2, 3)), 0);
+  EXPECT_EQ(mtx::to_int(mtx::rational(3, 3)), 1);
+
+  EXPECT_EQ(mtx::to_uint(mtx::rational(0, 3)), 0);
+  EXPECT_EQ(mtx::to_uint(mtx::rational(1, 3)), 0);
+  EXPECT_EQ(mtx::to_uint(mtx::rational(2, 3)), 0);
+  EXPECT_EQ(mtx::to_uint(mtx::rational(3, 3)), 1);
+}
+
+TEST(Math, ToIntRounding) {
+  EXPECT_EQ(mtx::to_int_rounded(mtx::rational(-0, 3)), -0);
+  EXPECT_EQ(mtx::to_int_rounded(mtx::rational(-1, 3)), -0);
+  EXPECT_EQ(mtx::to_int_rounded(mtx::rational(-2, 3)), -1);
+  EXPECT_EQ(mtx::to_int_rounded(mtx::rational(-3, 3)), -1);
+
+  EXPECT_EQ(mtx::to_int_rounded(mtx::rational(0, 3)), 0);
+  EXPECT_EQ(mtx::to_int_rounded(mtx::rational(1, 3)), 0);
+  EXPECT_EQ(mtx::to_int_rounded(mtx::rational(2, 3)), 1);
+  EXPECT_EQ(mtx::to_int_rounded(mtx::rational(3, 3)), 1);
+
+  EXPECT_EQ(mtx::to_uint_rounded(mtx::rational(0, 3)), 0);
+  EXPECT_EQ(mtx::to_uint_rounded(mtx::rational(1, 3)), 0);
+  EXPECT_EQ(mtx::to_uint_rounded(mtx::rational(2, 3)), 1);
+  EXPECT_EQ(mtx::to_uint_rounded(mtx::rational(3, 3)), 1);
+}
+
 }