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/* 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 3 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, see <http://www.gnu.org/licenses/>.
*
*/
#include "common/xpfloat.h"
#include "common/textconsole.h"
/*
Format:
s eeeeeeeeeeeeeee i fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
^ ^ ^ ^
| | | |
| Exponent (15) | Fraction (63)
Sign (1) Integer i (1)
MC68881 semantics:
e i f meaning
0 <= e <= 32766 1 any (-1)^s x 2^(e-16383) x (1.f) Normalized
0 <= e <= 32766 0 non-0 (-1)^s x 2^(e-16383) x (0.f) Denormalized
0 <= e <= 32766 0 0 (-1)^s x 0 Zero
32767 any 0 (-1)^s x Infinity Infinity
32767 any non-0 NaN NaN
*/
namespace Common {
XPFloat XPFloat::fromDouble(double value, Semantics semantics) {
uint64 bits;
memcpy(&bits, &value, 8);
return fromDoubleBits(bits, semantics);
}
XPFloat XPFloat::fromDoubleBits(uint64 inBits, Semantics semantics) {
uint64 inMantissa = inBits & 0xfffffffffffffu;
int16 inExponent = (inBits >> 52) & 0x7ff;
uint8 inSign = (inBits >> 63) & 1;
// Convert to 1.63 fraction and absolute exponent
uint64 workMantissa = 0;
int16 workExponent = 0;
if (inExponent == 0) {
if (inMantissa == 0) {
// +/- 0
return XPFloat(inSign << 15, 0);
} else {
// Subnormal
workMantissa = inMantissa << 11;
workExponent = -1022;
// Move implicit 1 to the high bit
while ((workMantissa & 0x8000000000000000u) == 0) {
workMantissa <<= 1;
workExponent--;
}
}
} else if (inExponent == 0x7ff) {
if (inMantissa == 0) {
// Infinity
return XPFloat((inSign << 15) | 0x7fffu, static_cast<uint64>(1) << 63);
} else {
// NaN
return XPFloat(0xFFFFu, 0xffffffffffffffffu);
}
} else {
// Normal number
workExponent = inExponent - 1023;
workMantissa = (inMantissa | 0x10000000000000) << 11;
}
return XPFloat((inSign << 15) | (workExponent + 16383), workMantissa);
}
void XPFloat::toDoubleSafe(double &result, bool &outOverflowed, Semantics semantics) const {
uint64 temp;
toDoubleBitsSafe(temp, outOverflowed, semantics);
memcpy(&result, &temp, 8);
}
void XPFloat::toDoubleBitsSafe(uint64 &result, bool &outOverflowed, Semantics semantics) const {
bool overflowed = false;
uint64 doubleBits = 0;
if ((signAndExponent & 0x7fff) == 0x7fff) {
if ((mantissa & 0x7fffffffffffffffu) == 0) {
// Infinity
doubleBits = (static_cast<uint64>(signAndExponent & 0x8000) << (63 - 15)) | 0x7ff0000000000000u;
} else {
// NaN
doubleBits = 0xffffffffffffffff;
}
} else {
// For MC68881 semantics, denormal and normal numbers are handled the same way because the
// i bit is effectively an explicit 1.
uint8 signBit = ((signAndExponent >> 15) & 1);
if (mantissa == 0) {
// +/- 0
doubleBits = static_cast<uint64>(signBit) << 63;
} else {
// Convert to 1.63
int32 workExponent = static_cast<int32>(signAndExponent & 0x7fff) - 16383;
uint64 workMantissa = mantissa;
while ((workMantissa & 0x8000000000000000u) == 0) {
workMantissa <<= 1;
workExponent--;
}
int32 adjustedExponent = workExponent + 1023;
if (adjustedExponent < 0) {
// Subnormal
int subnormalBits = -adjustedExponent;
if (subnormalBits > 52)
workMantissa = 0;
else
workMantissa >>= subnormalBits;
adjustedExponent = 0;
} else {
// Normal
if (adjustedExponent >= 0x7ff) {
// Overflow to +/- infinity
overflowed = true;
adjustedExponent = 0x7ff;
workMantissa = 0;
}
}
doubleBits = (static_cast<uint64>(signBit) << 63) | (static_cast<uint64>(adjustedExponent) << 52) | ((workMantissa >> 11) & 0xfffffffffffffu);
}
}
memcpy(&result, &doubleBits, 8);
outOverflowed = overflowed;
}
double XPFloat::toDouble(Semantics semantics) const {
double result;
bool overflowed;
toDoubleSafe(result, overflowed, semantics);
if (overflowed)
warning("Extended-precision floating point value was too large to represent as a double");
return result;
}
}
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