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| """Helper methods for working with Python Decimals.""" |
|
|
| import math |
| from decimal import Decimal |
| from typing import Optional, Union |
|
|
|
|
| def decimal_to_unscaled(value: Decimal) -> int: |
| """Get an unscaled value given a Decimal value. |
| |
| Args: |
| value (Decimal): A Decimal instance. |
| |
| Returns: |
| int: The unscaled value. |
| """ |
| sign, digits, _ = value.as_tuple() |
| return int(Decimal((sign, digits, 0)).to_integral_value()) |
|
|
|
|
| def unscaled_to_decimal(unscaled: int, scale: int) -> Decimal: |
| """Get a scaled Decimal value given an unscaled value and a scale. |
| |
| Args: |
| unscaled (int): An unscaled value. |
| scale (int): A scale to set for the returned Decimal instance. |
| |
| Returns: |
| Decimal: A scaled Decimal instance. |
| """ |
| sign, digits, _ = Decimal(unscaled).as_tuple() |
| return Decimal((sign, digits, -scale)) |
|
|
|
|
| def bytes_required(value: Union[int, Decimal]) -> int: |
| """Return the minimum number of bytes needed to serialize a decimal or unscaled value. |
| |
| Args: |
| value (int | Decimal): a Decimal value or unscaled int value. |
| |
| Returns: |
| int: the minimum number of bytes needed to serialize the value. |
| """ |
| if isinstance(value, int): |
| return (value.bit_length() + 8) // 8 |
| elif isinstance(value, Decimal): |
| return (decimal_to_unscaled(value).bit_length() + 8) // 8 |
|
|
| raise ValueError(f"Unsupported value: {value}") |
|
|
|
|
| def decimal_to_bytes(value: Decimal, byte_length: Optional[int] = None) -> bytes: |
| """Return a byte representation of a decimal. |
| |
| Args: |
| value (Decimal): a decimal value. |
| byte_length (int): The number of bytes. |
| Returns: |
| bytes: the unscaled value of the Decimal as bytes. |
| """ |
| unscaled_value = decimal_to_unscaled(value) |
| if byte_length is None: |
| byte_length = bytes_required(unscaled_value) |
| return unscaled_value.to_bytes(byte_length, byteorder="big", signed=True) |
|
|
|
|
| def bytes_to_decimal(value: bytes, scale: int) -> Decimal: |
| """Return a decimal from the bytes. |
| |
| Args: |
| value (bytes): tbe bytes to be converted into a decimal. |
| scale (int): the scale of the decimal. |
| |
| Returns: |
| Decimal: the scaled decimal. |
| """ |
| unscaled_datum = int.from_bytes(value, byteorder="big", signed=True) |
| return unscaled_to_decimal(unscaled_datum, scale) |
|
|
|
|
| def truncate_decimal(value: Decimal, width: int) -> Decimal: |
| """Get a truncated Decimal value given a decimal value and a width. |
| |
| Args: |
| value (Decimal): a decimal value. |
| width (int): A width for the returned Decimal instance. |
| Returns: |
| Decimal: A truncated Decimal instance. |
| """ |
| unscaled_value = decimal_to_unscaled(value) |
| applied_value = unscaled_value - (((unscaled_value % width) + width) % width) |
| return unscaled_to_decimal(applied_value, abs(int(value.as_tuple().exponent))) |
|
|
|
|
| MAX_PRECISION = tuple(math.floor(math.log10(math.fabs(math.pow(2, 8 * pos - 1) - 1))) for pos in range(24)) |
| REQUIRED_LENGTH = tuple(next(pos for pos in range(24) if p <= MAX_PRECISION[pos]) for p in range(40)) |
|
|
|
|
| def decimal_required_bytes(precision: int) -> int: |
| """Compute the number of bytes required to store a precision. |
| |
| Args: |
| precision: The number of digits to store. |
| |
| Returns: |
| The number of bytes required to store a decimal with a certain precision. |
| """ |
| if precision <= 0 or precision >= 40: |
| raise ValueError(f"Unsupported precision, outside of (0, 40]: {precision}") |
|
|
| return REQUIRED_LENGTH[precision] |
|
|
