/* ----------------------------------------------------------------------
* Copyright (C) 2010-2014 ARM Limited. All rights reserved.
*
* $Date: 16/10/14 6:01p $Revision:  V.1.4.5
*
* Project:      CMSIS DSP Library
* Title:        arm_fir_decimate_f32.c
*
* Description:  FIR decimation for floating-point sequences.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
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*   - Redistributions in binary form must reproduce the above copyright
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*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* -------------------------------------------------------------------- */

#include "arm_math.h"

/**
 * @ingroup groupFilters
 */

/**
 * @defgroup FIR_decimate Finite Impulse Response (FIR) Decimator
 *
 * These functions combine an FIR filter together with a decimator.
 * They are used in multirate systems for reducing the sample rate of a signal without introducing aliasing distortion.
 * Conceptually, the functions are equivalent to the block diagram below:
 * \image html FIRDecimator.gif "Components included in the FIR Decimator functions"
 * When decimating by a factor of <code>M</code>, the signal should be prefiltered by a lowpass filter with a normalized
 * cutoff frequency of <code>1/M</code> in order to prevent aliasing distortion.
 * The user of the function is responsible for providing the filter coefficients.
 *
 * The FIR decimator functions provided in the CMSIS DSP Library combine the FIR filter and the decimator in an efficient manner.
 * Instead of calculating all of the FIR filter outputs and discarding <code>M-1</code> out of every <code>M</code>, only the
 * samples output by the decimator are computed.
 * The functions operate on blocks of input and output data.
 * <code>pSrc</code> points to an array of <code>blockSize</code> input values and
 * <code>pDst</code> points to an array of <code>blockSize/M</code> output values.
 * In order to have an integer number of output samples <code>blockSize</code>
 * must always be a multiple of the decimation factor <code>M</code>.
 *
 * The library provides separate functions for Q15, Q31 and floating-point data types.
 *
 * \par Algorithm:
 * The FIR portion of the algorithm uses the standard form filter:
 * <pre>
 *    y[n] = b[0] * x[n] + b[1] * x[n-1] + b[2] * x[n-2] + ...+ b[numTaps-1] * x[n-numTaps+1]
 * </pre>
 * where, <code>b[n]</code> are the filter coefficients.
 * \par
 * The <code>pCoeffs</code> points to a coefficient array of size <code>numTaps</code>.
 * Coefficients are stored in time reversed order.
 * \par
 * <pre>
 *    {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}
 * </pre>
 * \par
 * <code>pState</code> points to a state array of size <code>numTaps + blockSize - 1</code>.
 * Samples in the state buffer are stored in the order:
 * \par
 * <pre>
 *    {x[n-numTaps+1], x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2]....x[0], x[1], ..., x[blockSize-1]}
 * </pre>
 * The state variables are updated after each block of data is processed, the coefficients are untouched.
 *
 * \par Instance Structure
 * The coefficients and state variables for a filter are stored together in an instance data structure.
 * A separate instance structure must be defined for each filter.
 * Coefficient arrays may be shared among several instances while state variable array should be allocated separately.
 * There are separate instance structure declarations for each of the 3 supported data types.
 *
 * \par Initialization Functions
 * There is also an associated initialization function for each data type.
 * The initialization function performs the following operations:
 * - Sets the values of the internal structure fields.
 * - Zeros out the values in the state buffer.
 * - Checks to make sure that the size of the input is a multiple of the decimation factor.
 * To do this manually without calling the init function, assign the follow subfields of the instance structure:
 * numTaps, pCoeffs, M (decimation factor), pState. Also set all of the values in pState to zero.
 *
 * \par
 * Use of the initialization function is optional.
 * However, if the initialization function is used, then the instance structure cannot be placed into a const data section.
 * To place an instance structure into a const data section, the instance structure must be manually initialized.
 * The code below statically initializes each of the 3 different data type filter instance structures
 * <pre>
 *arm_fir_decimate_instance_f32 S = {M, numTaps, pCoeffs, pState};
 *arm_fir_decimate_instance_q31 S = {M, numTaps, pCoeffs, pState};
 *arm_fir_decimate_instance_q15 S = {M, numTaps, pCoeffs, pState};
 * </pre>
 * where <code>M</code> is the decimation factor; <code>numTaps</code> is the number of filter coefficients in the filter;
 * <code>pCoeffs</code> is the address of the coefficient buffer;
 * <code>pState</code> is the address of the state buffer.
 * Be sure to set the values in the state buffer to zeros when doing static initialization.
 *
 * \par Fixed-Point Behavior
 * Care must be taken when using the fixed-point versions of the FIR decimate filter functions.
 * In particular, the overflow and saturation behavior of the accumulator used in each function must be considered.
 * Refer to the function specific documentation below for usage guidelines.
 */

/**
 * @addtogroup FIR_decimate
 * @{
 */

/**
 * @brief Processing function for the floating-point FIR decimator.
 * @param[in] *S        points to an instance of the floating-point FIR decimator structure.
 * @param[in] *pSrc     points to the block of input data.
 * @param[out] *pDst    points to the block of output data.
 * @param[in] blockSize number of input samples to process per call.
 * @return none.
 */

void arm_fir_decimate_f32(
    const arm_fir_decimate_instance_f32 * S,
    float32_t * pSrc,
    float32_t * pDst,
    uint32_t blockSize)
{
    float32_t *pState = S->pState;                 /* State pointer */
    float32_t *pCoeffs = S->pCoeffs;               /* Coefficient pointer */
    float32_t *pStateCurnt;                        /* Points to the current sample of the state */
    float32_t *px, *pb;                            /* Temporary pointers for state and coefficient buffers */
    float32_t sum0;                                /* Accumulator */
    float32_t x0, c0;                              /* Temporary variables to hold state and coefficient values */
    uint32_t numTaps = S->numTaps;                 /* Number of filter coefficients in the filter */
    uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M;  /* Loop counters */

#ifndef ARM_MATH_CM0_FAMILY

    uint32_t blkCntN4;
    float32_t *px0, *px1, *px2, *px3;
    float32_t acc0, acc1, acc2, acc3;
    float32_t x1, x2, x3;

    /* Run the below code for Cortex-M4 and Cortex-M3 */

    /* S->pState buffer contains previous frame (numTaps - 1) samples */
    /* pStateCurnt points to the location where the new input data should be written */
    pStateCurnt = S->pState + (numTaps - 1u);

    /* Total number of output samples to be computed */
    blkCnt = outBlockSize / 4;
    blkCntN4 = outBlockSize - (4 * blkCnt);

    while(blkCnt > 0u)
    {
        /* Copy 4 * decimation factor number of new input samples into the state buffer */
        i = 4 * S->M;

        do
        {
            *pStateCurnt++ = *pSrc++;

        }
        while(--i);

        /* Set accumulators to zero */
        acc0 = 0.0f;
        acc1 = 0.0f;
        acc2 = 0.0f;
        acc3 = 0.0f;

        /* Initialize state pointer for all the samples */
        px0 = pState;
        px1 = pState + S->M;
        px2 = pState + 2 * S->M;
        px3 = pState + 3 * S->M;

        /* Initialize coeff pointer */
        pb = pCoeffs;

        /* Loop unrolling.  Process 4 taps at a time. */
        tapCnt = numTaps >> 2;

        /* Loop over the number of taps.  Unroll by a factor of 4.
         ** Repeat until we've computed numTaps-4 coefficients. */

        while(tapCnt > 0u)
        {
            /* Read the b[numTaps-1] coefficient */
            c0 = *(pb++);

            /* Read x[n-numTaps-1] sample for acc0 */
            x0 = *(px0++);
            /* Read x[n-numTaps-1] sample for acc1 */
            x1 = *(px1++);
            /* Read x[n-numTaps-1] sample for acc2 */
            x2 = *(px2++);
            /* Read x[n-numTaps-1] sample for acc3 */
            x3 = *(px3++);

            /* Perform the multiply-accumulate */
            acc0 += x0 * c0;
            acc1 += x1 * c0;
            acc2 += x2 * c0;
            acc3 += x3 * c0;

            /* Read the b[numTaps-2] coefficient */
            c0 = *(pb++);

            /* Read x[n-numTaps-2] sample for acc0, acc1, acc2, acc3 */
            x0 = *(px0++);
            x1 = *(px1++);
            x2 = *(px2++);
            x3 = *(px3++);

            /* Perform the multiply-accumulate */
            acc0 += x0 * c0;
            acc1 += x1 * c0;
            acc2 += x2 * c0;
            acc3 += x3 * c0;

            /* Read the b[numTaps-3] coefficient */
            c0 = *(pb++);

            /* Read x[n-numTaps-3] sample acc0, acc1, acc2, acc3 */
            x0 = *(px0++);
            x1 = *(px1++);
            x2 = *(px2++);
            x3 = *(px3++);

            /* Perform the multiply-accumulate */
            acc0 += x0 * c0;
            acc1 += x1 * c0;
            acc2 += x2 * c0;
            acc3 += x3 * c0;

            /* Read the b[numTaps-4] coefficient */
            c0 = *(pb++);

            /* Read x[n-numTaps-4] sample acc0, acc1, acc2, acc3 */
            x0 = *(px0++);
            x1 = *(px1++);
            x2 = *(px2++);
            x3 = *(px3++);

            /* Perform the multiply-accumulate */
            acc0 += x0 * c0;
            acc1 += x1 * c0;
            acc2 += x2 * c0;
            acc3 += x3 * c0;

            /* Decrement the loop counter */
            tapCnt--;
        }

        /* If the filter length is not a multiple of 4, compute the remaining filter taps */
        tapCnt = numTaps % 0x4u;

        while(tapCnt > 0u)
        {
            /* Read coefficients */
            c0 = *(pb++);

            /* Fetch  state variables for acc0, acc1, acc2, acc3 */
            x0 = *(px0++);
            x1 = *(px1++);
            x2 = *(px2++);
            x3 = *(px3++);

            /* Perform the multiply-accumulate */
            acc0 += x0 * c0;
            acc1 += x1 * c0;
            acc2 += x2 * c0;
            acc3 += x3 * c0;

            /* Decrement the loop counter */
            tapCnt--;
        }

        /* Advance the state pointer by the decimation factor
         * to process the next group of decimation factor number samples */
        pState = pState + 4 * S->M;

        /* The result is in the accumulator, store in the destination buffer. */
        *pDst++ = acc0;
        *pDst++ = acc1;
        *pDst++ = acc2;
        *pDst++ = acc3;

        /* Decrement the loop counter */
        blkCnt--;
    }

    while(blkCntN4 > 0u)
    {
        /* Copy decimation factor number of new input samples into the state buffer */
        i = S->M;

        do
        {
            *pStateCurnt++ = *pSrc++;

        }
        while(--i);

        /* Set accumulator to zero */
        sum0 = 0.0f;

        /* Initialize state pointer */
        px = pState;

        /* Initialize coeff pointer */
        pb = pCoeffs;

        /* Loop unrolling.  Process 4 taps at a time. */
        tapCnt = numTaps >> 2;

        /* Loop over the number of taps.  Unroll by a factor of 4.
         ** Repeat until we've computed numTaps-4 coefficients. */
        while(tapCnt > 0u)
        {
            /* Read the b[numTaps-1] coefficient */
            c0 = *(pb++);

            /* Read x[n-numTaps-1] sample */
            x0 = *(px++);

            /* Perform the multiply-accumulate */
            sum0 += x0 * c0;

            /* Read the b[numTaps-2] coefficient */
            c0 = *(pb++);

            /* Read x[n-numTaps-2] sample */
            x0 = *(px++);

            /* Perform the multiply-accumulate */
            sum0 += x0 * c0;

            /* Read the b[numTaps-3] coefficient */
            c0 = *(pb++);

            /* Read x[n-numTaps-3] sample */
            x0 = *(px++);

            /* Perform the multiply-accumulate */
            sum0 += x0 * c0;

            /* Read the b[numTaps-4] coefficient */
            c0 = *(pb++);

            /* Read x[n-numTaps-4] sample */
            x0 = *(px++);

            /* Perform the multiply-accumulate */
            sum0 += x0 * c0;

            /* Decrement the loop counter */
            tapCnt--;
        }

        /* If the filter length is not a multiple of 4, compute the remaining filter taps */
        tapCnt = numTaps % 0x4u;

        while(tapCnt > 0u)
        {
            /* Read coefficients */
            c0 = *(pb++);

            /* Fetch 1 state variable */
            x0 = *(px++);

            /* Perform the multiply-accumulate */
            sum0 += x0 * c0;

            /* Decrement the loop counter */
            tapCnt--;
        }

        /* Advance the state pointer by the decimation factor
         * to process the next group of decimation factor number samples */
        pState = pState + S->M;

        /* The result is in the accumulator, store in the destination buffer. */
        *pDst++ = sum0;

        /* Decrement the loop counter */
        blkCntN4--;
    }

    /* Processing is complete.
     ** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
     ** This prepares the state buffer for the next function call. */

    /* Points to the start of the state buffer */
    pStateCurnt = S->pState;

    i = (numTaps - 1u) >> 2;

    /* copy data */
    while(i > 0u)
    {
        *pStateCurnt++ = *pState++;
        *pStateCurnt++ = *pState++;
        *pStateCurnt++ = *pState++;
        *pStateCurnt++ = *pState++;

        /* Decrement the loop counter */
        i--;
    }

    i = (numTaps - 1u) % 0x04u;

    /* copy data */
    while(i > 0u)
    {
        *pStateCurnt++ = *pState++;

        /* Decrement the loop counter */
        i--;
    }

#else

    /* Run the below code for Cortex-M0 */

    /* S->pState buffer contains previous frame (numTaps - 1) samples */
    /* pStateCurnt points to the location where the new input data should be written */
    pStateCurnt = S->pState + (numTaps - 1u);

    /* Total number of output samples to be computed */
    blkCnt = outBlockSize;

    while(blkCnt > 0u)
    {
        /* Copy decimation factor number of new input samples into the state buffer */
        i = S->M;

        do
        {
            *pStateCurnt++ = *pSrc++;

        }
        while(--i);

        /* Set accumulator to zero */
        sum0 = 0.0f;

        /* Initialize state pointer */
        px = pState;

        /* Initialize coeff pointer */
        pb = pCoeffs;

        tapCnt = numTaps;

        while(tapCnt > 0u)
        {
            /* Read coefficients */
            c0 = *pb++;

            /* Fetch 1 state variable */
            x0 = *px++;

            /* Perform the multiply-accumulate */
            sum0 += x0 * c0;

            /* Decrement the loop counter */
            tapCnt--;
        }

        /* Advance the state pointer by the decimation factor
         * to process the next group of decimation factor number samples */
        pState = pState + S->M;

        /* The result is in the accumulator, store in the destination buffer. */
        *pDst++ = sum0;

        /* Decrement the loop counter */
        blkCnt--;
    }

    /* Processing is complete.
     ** Now copy the last numTaps - 1 samples to the start of the state buffer.
     ** This prepares the state buffer for the next function call. */

    /* Points to the start of the state buffer */
    pStateCurnt = S->pState;

    /* Copy numTaps number of values */
    i = (numTaps - 1u);

    /* copy data */
    while(i > 0u)
    {
        *pStateCurnt++ = *pState++;

        /* Decrement the loop counter */
        i--;
    }

#endif /*   #ifndef ARM_MATH_CM0_FAMILY        */

}

/**
 * @} end of FIR_decimate group
 */
