SWORD25: Create a set of functions for manually serializing a double

Since we can't assume IEEE.

2 files changed, 233 insertions, 0 deletions

diff --git a/engines/sword25/util/double_serializer.cpp b/engines/sword25/util/double_serializer.cpp
new file mode 100644
index 0000000000..d7ba4f3052
--- /dev/null
+++ b/engines/sword25/util/double_serializer.cpp
@@ -0,0 +1,138 @@
+/* ScummVM - Graphic Adventure Engine
+ *
+ * ScummVM is the legal property of its developers, whose names
+ * are too numerous to list here. Please refer to the COPYRIGHT
+ * file distributed with this source distribution.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ */
+
+#include "sword25/util/double_serializer.h"
+
+#include "common/scummsys.h"
+
+
+namespace Util {
+
+SerializedDouble encodeDouble(double value) {
+	// Split the value into its significand and exponent
+	int exponent;
+	double significand = frexp(value, &exponent);
+
+	// Shift the the first part of the significand into the integer range
+	double shiftedsignificandPart = ldexp(abs(significand), 32);
+	uint32 significandOne = uint32(floor(shiftedsignificandPart));
+
+	// Shift the remainder of the significand into the integer range
+	shiftedsignificandPart -= significandOne;
+	uint32 significandTwo = (uint32)(ldexp(shiftedsignificandPart, 31));
+
+	SerializedDouble returnValue;
+	returnValue.significandOne = significandOne;                                // SignificandOne
+	returnValue.signAndSignificandTwo = ((uint32)(value < 0 ? 1 : 0) << 31) |   // Sign
+	                                    significandTwo;                         // SignificandTwo
+	returnValue.exponent = (int16)exponent;
+	return returnValue;
+}
+
+double decodeDouble(SerializedDouble value) {
+	// Expand the exponent and the parts of the significand
+	int exponent = (int)value.exponent;
+	double expandedsignificandOne = (double)value.significandOne;
+	double expandedsignificandTwo = (double)(value.signAndSignificandTwo & 0x7FFFFFFF);
+
+	// Deflate the significand
+	double shiftedsignificand = ldexp(expandedsignificandTwo, -21);
+	double significand = ldexp(expandedsignificandOne + shiftedsignificand, -32);
+
+	// Re-calculate the actual double
+	double returnValue = ldexp(significand, exponent);
+
+	// Check the sign bit and return
+	return ((value.signAndSignificandTwo & 0x80000000) == 0x80000000) ? -returnValue : returnValue;
+}
+
+uint64 encodeDouble_64(double value) {
+	// Split the value into its significand and exponent
+	int exponent;
+	double significand = frexp(value, &exponent);
+
+	// Shift the significand into the integer range
+	double shiftedsignificand = ldexp(abs(significand), 53);
+
+	// Combine everything using the IEEE standard
+	uint64 uintsignificand = (uint64)shiftedsignificand;
+	return ((uint64)(value < 0 ? 1 : 0) << 63) |        // Sign
+	       ((uint64)(exponent + 1023) << 52) |          // Exponent stored as an offset to 1023
+	       (uintsignificand & 0x000FFFFFFFFFFFFF);      // significand with MSB inferred
+}
+
+double decodeDouble_64(uint64 value) {
+	// Expand the exponent and significand
+	int exponent = (int)((value >> 52) & 0x7FF) - 1023;
+	double expandedsignificand = (double)(0x10000000000000 /* Inferred MSB */ | (value & 0x000FFFFFFFFFFFFF));
+
+	// Deflate the significand
+	int temp;
+	double significand = frexp(expandedsignificand, &temp);
+
+	// Re-calculate the actual double
+	double returnValue = ldexp(significand, exponent);
+
+	// Check the sign bit and return
+	return ((value & 0x8000000000000000) == 0x8000000000000000) ? -returnValue : returnValue;
+}
+
+CompactSerializedDouble encodeDouble_Compact(double value) {
+	// Split the value into its significand and exponent
+	int exponent;
+	double significand = frexp(value, &exponent);
+
+	// Shift the the first part of the significand into the integer range
+	double shiftedsignificandPart = ldexp(abs(significand), 32);
+	uint32 significandOne = uint32(floor(shiftedsignificandPart));
+
+	// Shift the remainder of the significand into the integer range
+	shiftedsignificandPart -= significandOne;
+	uint32 significandTwo = (uint32)(ldexp(shiftedsignificandPart, 21));
+
+	CompactSerializedDouble returnValue;
+	returnValue.signAndSignificandOne = ((uint32)(value < 0 ? 1 : 0) << 31) |   // Sign
+	                                    (significandOne & 0x7FFFFFFF);          // significandOne with MSB inferred
+	// Exponent stored as an offset to 1023
+	returnValue.exponentAndSignificandTwo = ((uint32)(exponent + 1023) << 21) | significandTwo;
+
+	return returnValue;
+}
+
+double decodeDouble_Compact(CompactSerializedDouble value) {
+	// Expand the exponent and the parts of the significand
+	int exponent = (int)(value.exponentAndSignificandTwo >> 21) - 1023;
+	double expandedsignificandOne = (double)(0x80000000 /* Inferred MSB */ | (value.signAndSignificandOne & 0x7FFFFFFF));
+	double expandedsignificandTwo = (double)(value.exponentAndSignificandTwo & 0x1FFFFF);
+
+	// Deflate the significand
+	double shiftedsignificand = ldexp(expandedsignificandTwo, -21);
+	double significand = ldexp(expandedsignificandOne + shiftedsignificand, -32);
+
+	// Re-calculate the actual double
+	double returnValue = ldexp(significand, exponent);
+
+	// Check the sign bit and return
+	return ((value.signAndSignificandOne & 0x80000000) == 0x80000000) ? -returnValue : returnValue;
+}
+
+} // End of namespace Sword25
diff --git a/engines/sword25/util/double_serializer.h b/engines/sword25/util/double_serializer.h
new file mode 100644
index 0000000000..e90338c369
--- /dev/null
+++ b/engines/sword25/util/double_serializer.h
@@ -0,0 +1,95 @@
+/* ScummVM - Graphic Adventure Engine
+ *
+ * ScummVM is the legal property of its developers, whose names
+ * are too numerous to list here. Please refer to the COPYRIGHT
+ * file distributed with this source distribution.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ */
+
+#ifndef DOUBLE_SERIALIZATION_H
+#define DOUBLE_SERIALIZATION_H
+
+#include "common/types.h"
+
+
+namespace Util {
+
+struct SerializedDouble {
+	uint32 significandOne;
+	uint32 signAndSignificandTwo;
+	int16 exponent;
+};
+
+struct CompactSerializedDouble {
+	uint32 signAndSignificandOne;
+	uint32 exponentAndSignificandTwo;
+};
+
+/**
+ * Encodes a double as two uint32 and a one int16
+ *
+ * Supports denormalized numbers. Does NOT support NaN, or Inf
+ *
+ * @param value    The value to encode
+ * @return         The encoded value
+ */
+SerializedDouble encodeDouble(double value);
+/**
+ * Decodes a previously encoded double
+ *
+ * @param value    The value to decode
+ * @return         The decoded value
+ */
+double decodeDouble(SerializedDouble value);
+
+/**
+ * Encodes a double as a uint64
+ *
+ * Does NOT support denormalized numbers. Does NOT support NaN, or Inf
+ *
+ * @param value    The value to encode
+ * @return         The encoded value
+ */
+uint64 encodeDouble_64(double value);
+/**
+ * Decodes a previously encoded double
+ *
+ * @param value    The value to decode
+ * @return         The decoded value
+ */
+double decodeDouble_64(uint64 value);
+
+/**
+ * Encodes a double as two uint32
+ *
+ * Does NOT support denormalized numbers. Does NOT support NaN, or Inf
+ *
+ * @param value    The value to encode
+ * @return         The encoded value
+ */
+CompactSerializedDouble encodeDouble_Compact(double value);
+/**
+ * Decodes a previously encoded double
+ *
+ * @param value    The value to decode
+ * @return         The decoded value
+ */
+double decodeDouble_Compact(CompactSerializedDouble value);
+
+} // End of namespace Sword25
+
+#endif