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105 lines
3.6 KiB
Python
105 lines
3.6 KiB
Python
from hachoir.field import Bit, Bits, FieldSet
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from hachoir.core.endian import BIG_ENDIAN, LITTLE_ENDIAN
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import struct
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# Make sure that we use right struct types
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assert struct.calcsize("f") == 4
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assert struct.calcsize("d") == 8
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assert struct.unpack("<d", b"\x1f\x85\xebQ\xb8\x1e\t@")[0] == 3.14
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assert struct.unpack(">d", b"\xc0\0\0\0\0\0\0\0")[0] == -2.0
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class FloatMantissa(Bits):
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def createValue(self):
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value = Bits.createValue(self)
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return 1 + float(value) / (2 ** self.size)
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def createRawDisplay(self):
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return str(Bits.createValue(self))
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class FloatExponent(Bits):
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def __init__(self, parent, name, size):
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Bits.__init__(self, parent, name, size)
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self.bias = 2 ** (size - 1) - 1
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def createValue(self):
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return Bits.createValue(self) - self.bias
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def createRawDisplay(self):
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return str(self.value + self.bias)
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def floatFactory(name, format, mantissa_bits, exponent_bits, doc):
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size = 1 + mantissa_bits + exponent_bits
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class Float(FieldSet):
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static_size = size
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__doc__ = doc
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def __init__(self, parent, name, description=None):
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assert parent.endian in (BIG_ENDIAN, LITTLE_ENDIAN)
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FieldSet.__init__(self, parent, name, description, size)
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if format:
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if self._parent.endian == BIG_ENDIAN:
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self.struct_format = ">" + format
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else:
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self.struct_format = "<" + format
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else:
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self.struct_format = None
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def createValue(self):
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"""
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Create float value: use struct.unpack() when it's possible
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(32 and 64-bit float) or compute it with :
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mantissa * (2.0 ** exponent)
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This computation may raise an OverflowError.
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"""
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if self.struct_format:
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raw = self._parent.stream.readBytes(
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self.absolute_address, self._size // 8)
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try:
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return struct.unpack(self.struct_format, raw)[0]
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except struct.error as err:
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raise ValueError("[%s] conversion error: %s" %
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(self.__class__.__name__, err))
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else:
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try:
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value = self["mantissa"].value * \
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(2.0 ** float(self["exponent"].value))
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if self["negative"].value:
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return -(value)
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else:
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return value
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except OverflowError:
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raise ValueError("[%s] floating point overflow" %
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self.__class__.__name__)
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def createFields(self):
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yield Bit(self, "negative")
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yield FloatExponent(self, "exponent", exponent_bits)
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if 64 <= mantissa_bits:
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yield Bit(self, "one")
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yield FloatMantissa(self, "mantissa", mantissa_bits - 1)
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else:
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yield FloatMantissa(self, "mantissa", mantissa_bits)
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cls = Float
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cls.__name__ = name
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return cls
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# 32-bit float (standard: IEEE 754/854)
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Float32 = floatFactory("Float32", "f", 23, 8,
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"Floating point number: format IEEE 754 int 32 bit")
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# 64-bit float (standard: IEEE 754/854)
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Float64 = floatFactory("Float64", "d", 52, 11,
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"Floating point number: format IEEE 754 in 64 bit")
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# 80-bit float (standard: IEEE 754/854)
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Float80 = floatFactory("Float80", None, 64, 15,
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"Floating point number: format IEEE 754 in 80 bit")
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