1 files changed, 136 insertions, 0 deletions
diff --git a/src/util/ieee_float.cpp b/src/util/ieee_float.cpp
new file mode 100644
index 000000000..e7909360f
--- /dev/null
+++ b/src/util/ieee_float.cpp
@@ -0,0 +1,136 @@
+/*
+ * Conversion of f32 to IEEE-754 and vice versa.
+ *
+ * © Copyright 2018 Pedro Gimeno Fortea.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+ * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+#include "ieee_float.h"
+#include "log.h"
+#include "porting.h"
+#include <limits>
+#include <cmath>
+
+// Given an unsigned 32-bit integer representing an IEEE-754 single-precision
+// float, return the float.
+f32 u32Tof32Slow(u32 i)
+{
+	// clang-format off
+	int exp = (i >> 23) & 0xFF;
+	u32 sign = i & 0x80000000UL;
+	u32 imant = i & 0x7FFFFFUL;
+	if (exp == 0xFF) {
+		// Inf/NaN
+		if (imant == 0) {
+			if (std::numeric_limits<f32>::has_infinity)	
+				return sign ? -std::numeric_limits<f32>::infinity() :
+					std::numeric_limits<f32>::infinity();
+			return sign ? std::numeric_limits<f32>::max() :
+				std::numeric_limits<f32>::lowest();
+		}
+		return std::numeric_limits<f32>::has_quiet_NaN ?
+			std::numeric_limits<f32>::quiet_NaN() : -0.f;
+	}
+
+	if (!exp) {
+		// Denormal or zero
+		return sign ? -ldexpf((f32)imant, -149) : ldexpf((f32)imant, -149);
+	}
+
+	return sign ? -ldexpf((f32)(imant | 0x800000UL), exp - 150) :
+		ldexpf((f32)(imant | 0x800000UL), exp - 150);
+	// clang-format on
+}
+
+// Given a float, return an unsigned 32-bit integer representing the f32
+// in IEEE-754 single-precision format.
+u32 f32Tou32Slow(f32 f)
+{
+	u32 signbit = std::copysign(1.0f, f) == 1.0f ? 0 : 0x80000000UL;
+	if (f == 0.f)
+		return signbit;
+	if (std::isnan(f))
+		return signbit | 0x7FC00000UL;
+	if (std::isinf(f))
+		return signbit | 0x7F800000UL;
+	int exp;
+	f32 mant = frexpf(f, &exp);
+	u32 imant = (u32)std::floor((signbit ? -16777216.f : 16777216.f) * mant);
+	exp += 126;
+	if (exp <= 0) {
+		// Denormal
+		return signbit | (exp <= -31 ? 0 : imant >> (1 - exp));
+	}
+
+	if (exp >= 255) {
+		// Overflow due to the platform having exponents bigger than IEEE ones.
+		// Return signed infinity.
+		return signbit | 0x7F800000UL;
+	}
+
+	// Regular number
+	return signbit | (exp << 23) | (imant & 0x7FFFFFUL);
+}
+
+// This test needs the following requisites in order to work:
+// - The float type must be a 32 bits IEEE-754 single-precision float.
+// - The endianness of f32s and integers must match.
+FloatType getFloatSerializationType()
+{
+	// clang-format off
+	const f32 cf = -22220490.f;
+	const u32 cu = 0xCBA98765UL;
+	if (std::numeric_limits<f32>::is_iec559 && sizeof(cf) == 4 &&
+			sizeof(cu) == 4 && !memcmp(&cf, &cu, 4)) {
+		// u32Tof32Slow and f32Tou32Slow are not needed, use memcpy
+		return FLOATTYPE_SYSTEM;
+	}
+
+	// Run quick tests to ensure the custom functions provide acceptable results
+	warningstream << "floatSerialization: f32 and u32 endianness are "
+		"not equal or machine is not IEEE-754 compliant" << std::endl;
+	u32 i;
+	char buf[128];
+
+	// NaN checks aren't included in the main loop
+	if (!std::isnan(u32Tof32Slow(0x7FC00000UL))) {
+		porting::mt_snprintf(buf, sizeof(buf),
+			"u32Tof32Slow(0x7FC00000) failed to produce a NaN, actual: %.9g",
+			u32Tof32Slow(0x7FC00000UL));
+		infostream << buf << std::endl;
+	}
+	if (!std::isnan(u32Tof32Slow(0xFFC00000UL))) {
+		porting::mt_snprintf(buf, sizeof(buf),
+			"u32Tof32Slow(0xFFC00000) failed to produce a NaN, actual: %.9g",
+			u32Tof32Slow(0xFFC00000UL));
+		infostream << buf << std::endl;
+	}
+
+	i = f32Tou32Slow(std::numeric_limits<f32>::quiet_NaN());
+	// check that it corresponds to a NaN encoding
+	if ((i & 0x7F800000UL) != 0x7F800000UL || (i & 0x7FFFFFUL) == 0) {
+		porting::mt_snprintf(buf, sizeof(buf),
+			"f32Tou32Slow(NaN) failed to encode NaN, actual: 0x%X", i);
+		infostream << buf << std::endl;
+	}
+
+	return FLOATTYPE_SLOW;
+	// clang-format on
+}