CxxUtils::FloatPacker Class Reference

Pack/unpack floating-point data from/to a given number of bits. More...

#include <FloatPacker.h>

List of all members.

Public Types
typedef uint32_t	Packdest
	Type into which we pack.
Public Member Functions
	FloatPacker (int nbits, int nmantissa, double scale=1, bool is_signed=true, bool round=false)
	Constructor.
bool	errcheck (std::string &err) const
	Check to see if an error occurred.
Packdest	pack (double src) const
	Pack a value.
double	unpack (Packdest val) const
	Unpack the value VAL.

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Detailed Description

Pack/unpack floating-point data from/to a given number of bits.

The format is specified by the following parameters.

nbits - The total number of bits in the representation. scale - Scale factor to apply before storing. nmantissa - The number of bits to use for the mantissa and sign bit. is_signed - Flag to tell if we should use a sign bit. round - Flag to tell if we should round or truncate.

From these we derive:

npack = nmantissa, if is_signed is false. = nmantissa-1 if is_signed is true. nexp = nbits - nmantissa

The format consists of, in order from high bits to low bits:

• A sign bit, if is_signed is true.
• nexp bits of exponent information.
• npack bits of mantissa.

The number is stored in normalized form, with an exponent bias of 2^(nexp-1). But if the (biased) exponent is zero, then the mantissa is stored in denormalized form. If nexp==0, this gives a fixed-point representation in the range [0,1). 0 is represented by all bits 0; if we have a sign bit, we can also represent -0 by all bits 0 except for the sign bit.

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Constructor & Destructor Documentation

CxxUtils::FloatPacker::FloatPacker	(	int	nbits,
		int	nmantissa,
		double	scale = 1,
		bool	is_signed = true,
		bool	round = false
	)

Constructor.

Parameters:

	nbits	The number of bits in the packed representation.
	nmantissa	The number of bits to use for the mantissa and sign bit.
	scale	Divide the input number by this before packing.
	is_signed	If true, then one mantissa bit is used for a sign.
	round	If true, numbers will be rounded. Otherwise, they will be truncated.

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Member Function Documentation

bool CxxUtils::FloatPacker::errcheck

(

std::string &

err

)

const

Check to see if an error occurred.

Parameters:

err[out]

If an error occurred, a description of it.

Returns:

True if an error occurred since the last call to errcheck.

FloatPacker::Packdest CxxUtils::FloatPacker::pack

(

double

src

)

const

Pack a value.

Parameters:

src

Value to pack.

Returns:

The packed value.

For now, we convert floats to doubles before packing.

double CxxUtils::FloatPacker::unpack

(

Packdest

val

)

const

Unpack the value VAL.

Parameters:

val

The packed data. It should start with the low bit, and any extraneous bits should have been masked off.

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The documentation for this class was generated from the following files:

• /cvmfs/atlas.cern.ch/repo/sw/ASG/AnalysisBase/2.4.31/CxxUtils/CxxUtils/FloatPacker.h
• /cvmfs/atlas.cern.ch/repo/sw/ASG/AnalysisBase/2.4.31/CxxUtils/Root/FloatPacker.cxx