bfrt_helper.util

Functions

encode_number

encode_number(number, bitwidth)

Convert an integer to it’s representation in bytes.

gRPC operations involving values are always sent as bytes. Since operations internally to the helpers are performed on integers (it is way easier), values need to be ‘casted’ to bytes.

The byte string will always be the smallest number of bytes capable of holding the value based upon the bitwidth. If a value is provided that is out of range, an exception will be thrown.

The number of bytes is calculated as:

\[[ (b + 8 - 1) / b ]\]

Where \(b\) is the bitwidth.

Conversion to bytes is performed via the int.to_bytes method, using a big endian conversion.

Parameters:

• number (int) – Value to convert

• bitwidth (int) – Bitwidth of the field

Raises:

ValueOutOfRange – The supplied value exceeds the maximum number the bitwidth is capable of supporting.

bit_not

bit_not(value, n_bits)

Calculates the bitwise negation (NOT) of an integer.

Since integers in python are both signed and have arbitrary lengths, calculating the bitwsie negation is not straightforward.

The is calculated by:

\[(2^b-1) - x\]

Where \(b\) is the number of bits in the value and \(x\) is the value to convert.

Note

This will not work on negative numbers.

Parameters:

• value (int) – The value to convert.

• n_bits (int) – The number of bits the value should have.

mask_from_prefix

mask_from_prefix(bitwidth, prefix)

Calculates a mask for the given bitwidth and prefix.

\[2^{p-1} \ll (w - p)\]

Exceptions

InvalidValue

class InvalidValue(message)

Bases: Exception

InvalidOperation

class InvalidOperation(message)

Bases: Exception

ValueOutOfRange

class ValueOutOfRange(message)

Bases: Exception

MatchHelper

class MatchHelper(*types)

Bases: object