Q function

pyfxp.Q

Q(qi, qf, signed=True, rnd=TRUNC, ovf=WRAP)

Create a fixed-point format specification using ARM-style Q-format notation.

The Q function defines a fixed-point representation by specifying the number of integer and fractional bits, whether the format is signed, and how rounding and overflow are handled. It returns an FxpSpec object that can be passed to other functions (e.g., fxp) for actual numeric conversion.

Parameters:

Name	Type	Description	Default
qi	int	Number of integer bits.	required
qf	int	Number of fractional bits.	required
signed	bool	Whether the fixed-point format is signed (default is True).	True
rnd	int	Rounding method to apply (default is TRUNC (0)). Supported methods: TRUNC (0): Bit truncation (rounds toward negative infinity) CEIL (1): Round toward positive infinity TO_ZERO (2): Round toward zero AWAY (3): Round away from zero HALF_UP (4): Round to nearest; ties toward positive infinity HALF_DOWN (5): Round to nearest; ties toward negative infinity HALF_EVEN (6): Round to nearest; ties to even HALF_ZERO (7): Round to nearest; ties toward zero HALF_AWAY (8): Round to nearest; ties away from zero	TRUNC
ovf	int	Overflow handling method (default is WRAP (0)). Supported methods: WRAP (0): Wrap around on overflow (modulo behavior) SAT (1): Saturate to maximum/minimum representable value ERROR (2): Raise an error if overflow occurs	WRAP

Returns:

Type	Description
FxpSpec	A specification object describing the fixed-point format.

Notes

This function uses ARM-style Q-format notation:

• Qm.n indicates m integer bits and n fractional bits (ARM style).
• The returned FxpSpec can be reused for consistent conversions across multiple values.

Examples:

>>> spec = Q(3, 1)  # Q3.5 format (3 integer bits, 5 fractional bits)
>>> spec.qi, spec.qf
(3, 1)
>>> fxp(1.25, spec)
1.0