linux/drivers/misc/echo/fir.h

/* SPDX-License-Identifier: GPL-2.0-only */
/*
 * SpanDSP - a series of DSP components for telephony
 *
 * fir.h - General telephony FIR routines
 *
 * Written by Steve Underwood <[email protected]>
 *
 * Copyright (C) 2002 Steve Underwood
 *
 * All rights reserved.
 */

#if !defined(_FIR_H_)
#define _FIR_H_

/*
   Ideas for improvement:

   1/ Rewrite filter for dual MAC inner loop.  The issue here is handling
   history sample offsets that are 16 bit aligned - the dual MAC needs
   32 bit aligmnent.  There are some good examples in libbfdsp.

   2/ Use the hardware circular buffer facility tohalve memory usage.

   3/ Consider using internal memory.

   Using less memory might also improve speed as cache misses will be
   reduced. A drop in MIPs and memory approaching 50% should be
   possible.

   The foreground and background filters currenlty use a total of
   about 10 MIPs/ch as measured with speedtest.c on a 256 TAP echo
   can.
*/

/*
 * 16 bit integer FIR descriptor. This defines the working state for a single
 * instance of an FIR filter using 16 bit integer coefficients.
 */
struct fir16_state_t { … };

/*
 * 32 bit integer FIR descriptor. This defines the working state for a single
 * instance of an FIR filter using 32 bit integer coefficients, and filtering
 * 16 bit integer data.
 */
struct fir32_state_t { … };

/*
 * Floating point FIR descriptor. This defines the working state for a single
 * instance of an FIR filter using floating point coefficients and data.
 */
struct fir_float_state_t { … };

static inline const int16_t *fir16_create(struct fir16_state_t *fir,
					      const int16_t *coeffs, int taps)
{ … }

static inline void fir16_flush(struct fir16_state_t *fir)
{ … }

static inline void fir16_free(struct fir16_state_t *fir)
{ … }

static inline int16_t fir16(struct fir16_state_t *fir, int16_t sample)
{ … }

static inline const int16_t *fir32_create(struct fir32_state_t *fir,
					      const int32_t *coeffs, int taps)
{ … }

static inline void fir32_flush(struct fir32_state_t *fir)
{ … }

static inline void fir32_free(struct fir32_state_t *fir)
{ … }

static inline int16_t fir32(struct fir32_state_t *fir, int16_t sample)
{ … }

#endif