Add ULP and margin matcher

Closes #1074

include/internal/catch_matchers_floating.cpp

@@ -0,0 +1,144 @@
+/*
+ *  Created by Martin on 07/11/2017.
+ *
+ * Distributed under the Boost Software License, Version 1.0. (See accompanying
+ * file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+ */
+
+#include "catch_matchers_floating.h"
+
+#include <cmath>
+#include <cstdint>
+#include <cstring>
+#include <stdexcept>
+
+namespace Catch {
+namespace Matchers {
+namespace Floating {
+enum class FloatingPointKind : uint8_t {
+    Float,
+    Double
+};
+}
+}
+}
+
+namespace {
+union Float_t {
+    Float_t(float num = 0.0f) : f(num) {}
+    // Portable extraction of components.
+    bool Negative() const { return i < 0; }
+    int32_t RawMantissa() const { return i & ((1 << 23) - 1); }
+    int32_t RawExponent() const { return (i >> 23) & 0xFF; }
+
+    int32_t i;
+    float f;
+};
+
+template <typename T>
+struct Converter;
+
+template <>
+struct Converter<float> {
+    static_assert(sizeof(float) == sizeof(int32_t), "Important ULP matcher assumption violated");
+    Converter(float f) {
+        std::memcpy(&i, &f, sizeof(f));
+    }
+    int32_t i;
+};
+
+template <>
+struct Converter<double> {
+    static_assert(sizeof(double) == sizeof(int64_t), "Important ULP matcher assumption violated");
+    Converter(double d) {
+        std::memcpy(&i, &d, sizeof(d));
+    }
+    int64_t i;
+};
+
+template <typename T>
+auto convert(T t) -> Converter<T> {
+    return Converter<T>(t);
+}
+
+template <typename FP>
+bool almostEqualUlps(FP lhs, FP rhs, int maxUlpDiff) {
+    // Comparison with NaN should always be false.
+    // This way we can rule it out before getting into the ugly details
+    if (std::isnan(lhs) || std::isnan(rhs)) {
+        return false;
+    }
+
+    auto lc = convert(lhs);
+    auto rc = convert(rhs);
+
+    if ((lc.i < 0) != (rc.i < 0)) {
+        // Potentially we can have +0 and -0
+        return lhs == rhs;
+    }
+
+    auto ulpDiff = abs(lc.i - rc.i);
+    return ulpDiff <= maxUlpDiff;
+}
+
+}
+
+
+namespace Catch {
+namespace Matchers {
+namespace Floating {
+    WithinAbsMatcher::WithinAbsMatcher(double target, double margin)
+        :m_target{ target }, m_margin{ margin } {}
+
+    // Performs equivalent check of std::fabs(lhs - rhs) <= margin
+    // But without the subtraction to allow for INFINITY in comparison
+    bool WithinAbsMatcher::match(double const& matchee) const {
+        return (matchee + m_margin >= m_target) && (m_target + m_margin >= m_margin);
+    }
+
+    std::string WithinAbsMatcher::describe() const {
+        return "is within " + std::to_string(m_margin) + " of " + std::to_string(m_target);
+    }
+
+
+    WithinUlpsMatcher::WithinUlpsMatcher(double target, int ulps, FloatingPointKind baseType)
+        :m_target{ target }, m_ulps{ ulps }, m_type{ baseType } {
+        if (m_ulps < 0) {
+            throw std::domain_error("Expected ulp difference has to be >0");
+        }
+    }
+
+    bool WithinUlpsMatcher::match(double const& matchee) const {
+        switch (m_type) {
+        case FloatingPointKind::Float:
+            return almostEqualUlps<float>(static_cast<float>(matchee), static_cast<float>(m_target), m_ulps);
+        case FloatingPointKind::Double:
+            return almostEqualUlps<double>(matchee, m_target, m_ulps);
+        default:
+            throw std::domain_error("Unknown FloatingPointKind value");
+        }
+    }
+
+    std::string WithinUlpsMatcher::describe() const {
+        return "is within " + std::to_string(m_ulps) + " ULPs of " + std::to_string(m_target) + ((m_type == FloatingPointKind::Float)? "f" : "");
+    }
+
+}// namespace Floating
+
+
+
+Floating::WithinUlpsMatcher WithinULP(double target, int maxUlpDiff) {
+    return Floating::WithinUlpsMatcher(target, maxUlpDiff, Floating::FloatingPointKind::Double);
+}
+
+Floating::WithinUlpsMatcher WithinULP(float target, int maxUlpDiff) {
+    return Floating::WithinUlpsMatcher(target, maxUlpDiff, Floating::FloatingPointKind::Float);
+}
+
+Floating::WithinAbsMatcher WithinAbs(double target, double margin) {
+    return Floating::WithinAbsMatcher(target, margin);
+}
+
+} // namespace Matchers
+} // namespace Catch
+