vad/fir_filter.py

import numpy as np


class FIR:
    """
    FIR (Finite Impulse Response) filter implementation
    Converted from C implementation in FIRFilter.c
    """

    def __init__(self, step_size):
        """Initialize the FIR filter"""
        self.N = step_size
        self.input_buffer = np.zeros(2 * step_size, dtype=float)


def check_range(input_val):
    """Limit the value to the range [-1.0, 1.0]"""
    if input_val > 1.0:
        return 1.0
    elif input_val < -1.0:
        return -1.0
    else:
        return input_val


def init_fir(step_size):
    """Create a new FIR filter instance"""
    return FIR(step_size)


def process_fir_filter(fir, input_signal, filter_coefficients):
    """
    Process input through the FIR filter

    Args:
        fir: FIR filter instance
        input_signal: Input signal array
        filter_coefficients: Filter coefficients array

    Returns:
        output_signal: Filtered output signal
    """
    # Create output array
    output = np.zeros(fir.N, dtype=float)

    # Update input buffer
    fir.input_buffer[: fir.N] = fir.input_buffer[fir.N :]
    fir.input_buffer[fir.N :] = input_signal

    # Apply FIR filter
    for i in range(fir.N):
        temp = 0.0
        for j in range(len(filter_coefficients)):
            idx = fir.N + (i - j)
            if idx >= 0 and idx < 2 * fir.N:  # Ensure index is in bounds
                temp += fir.input_buffer[idx] * filter_coefficients[j]
        output[i] = check_range(temp)

    return output


def destroy_fir(fir):
    """
    Clean up resources (not necessary in Python due to garbage collection)
    Included for API compatibility with C code
    """
    # In Python, memory management is automatic
    pass