FloatSpec<> implementation and tests

2026-10-21 11:53:33 +08:00 · 2014-02-22 15:06:08 +04:00
parent 1e1fdc613b
commit 51e42038c6
3 changed files with 399 additions and 0 deletions
@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2014 Pavel Kirienko <pavel.kirienko@gmail.com>
+ */
+
+#include <uavcan/internal/marshalling/float_spec.hpp>
+#include <cmath>
+
+namespace uavcan
+{
+/*
+ * IEEE754Converter
+ * Float16 conversion algorithm: http://half.sourceforge.net/ (MIT License)
+ * TODO: Use conversion tables (conditional compilation - it would require something like 10Kb+ ROM).
+ */
+template <typename T>
+static inline bool signbit(T arg)
+{
+    return arg < T(0) || (arg == T(0) && T(1) / arg < T(0));
+}
+
+uint16_t IEEE754Converter::nativeNonIeeeToHalf(float value)
+{
+    uint16_t hbits = signbit(value) << 15;
+    if (value == 0.0f)
+        return hbits;
+    if (isnanf(value))
+        return hbits | 0x7FFF;
+    if (isinff(value))
+        return hbits | 0x7C00;
+    int exp;
+    std::frexp(value, &exp);
+    if (exp > 16)
+        return hbits | 0x7C00;
+    if (exp < -13)
+        value = std::ldexp(value, 24);
+    else
+    {
+        value = std::ldexp(value, 11 - exp);
+        hbits |= ((exp + 14) << 10);
+    }
+    const int ival = static_cast<int>(value);
+    hbits |= static_cast<uint16_t>(std::abs(ival) & 0x3FF);
+    float diff = std::abs(value - static_cast<float>(ival));
+    hbits += diff >= 0.5f;
+    return hbits;
+}
+
+float IEEE754Converter::halfToNativeNonIeee(uint16_t value)
+{
+    float out;
+    int abs = value & 0x7FFF;
+    if (abs > 0x7C00)
+        out = std::numeric_limits<float>::has_quiet_NaN ? std::numeric_limits<float>::quiet_NaN() : 0.0f;
+    else if (abs == 0x7C00)
+        out = std::numeric_limits<float>::has_infinity ?
+                std::numeric_limits<float>::infinity() : std::numeric_limits<float>::max();
+    else if (abs > 0x3FF)
+        out = std::ldexp(static_cast<float>((value & 0x3FF) | 0x400), (abs >> 10) - 25);
+    else
+        out = std::ldexp(static_cast<float>(abs), -24);
+    return (value & 0x8000) ? -out : out;
+}
+
+}