| /* ---------------------------------------------------------------------- |
| * Copyright (C) 2010-2014 ARM Limited. All rights reserved. |
| * |
| * $Date: 19. March 2015 |
| * $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 |
| * are met: |
| * - Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * - Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in |
| * the documentation and/or other materials provided with the |
| * distribution. |
| * - Neither the name of ARM LIMITED nor the names of its contributors |
| * may be used to endorse or promote products derived from this |
| * software without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS |
| * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE |
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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 |
| */ |