pigweed / third_party / github / STMicroelectronics / cmsis_core / 7dd288b23bf605a3a2fafa81a29d2c96a2fd83ce / . / DSP_Lib / Source / FilteringFunctions / arm_fir_interpolate_f32.c

/* ---------------------------------------------------------------------- | |

* 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_interpolate_f32.c | |

* | |

* Description: FIR interpolation for floating-point sequences. | |

* | |

* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0 | |

* | |

* Redistribution and use in source and binary forms, with or without | |

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* | |

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* -------------------------------------------------------------------- */ | |

#include "arm_math.h" | |

/** | |

* @defgroup FIR_Interpolate Finite Impulse Response (FIR) Interpolator | |

* | |

* These functions combine an upsampler (zero stuffer) and an FIR filter. | |

* They are used in multirate systems for increasing the sample rate of a signal without introducing high frequency images. | |

* Conceptually, the functions are equivalent to the block diagram below: | |

* \image html FIRInterpolator.gif "Components included in the FIR Interpolator functions" | |

* After upsampling by a factor of <code>L</code>, the signal should be filtered by a lowpass filter with a normalized | |

* cutoff frequency of <code>1/L</code> in order to eliminate high frequency copies of the spectrum. | |

* The user of the function is responsible for providing the filter coefficients. | |

* | |

* The FIR interpolator functions provided in the CMSIS DSP Library combine the upsampler and FIR filter in an efficient manner. | |

* The upsampler inserts <code>L-1</code> zeros between each sample. | |

* Instead of multiplying by these zero values, the FIR filter is designed to skip them. | |

* This leads to an efficient implementation without any wasted effort. | |

* 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*L</code> output values. | |

* | |

* The library provides separate functions for Q15, Q31, and floating-point data types. | |

* | |

* \par Algorithm: | |

* The functions use a polyphase filter structure: | |

* <pre> | |

* y[n] = b[0] * x[n] + b[L] * x[n-1] + ... + b[L*(phaseLength-1)] * x[n-phaseLength+1] | |

* y[n+1] = b[1] * x[n] + b[L+1] * x[n-1] + ... + b[L*(phaseLength-1)+1] * x[n-phaseLength+1] | |

* ... | |

* y[n+(L-1)] = b[L-1] * x[n] + b[2*L-1] * x[n-1] + ....+ b[L*(phaseLength-1)+(L-1)] * x[n-phaseLength+1] | |

* </pre> | |

* This approach is more efficient than straightforward upsample-then-filter algorithms. | |

* With this method the computation is reduced by a factor of <code>1/L</code> when compared to using a standard FIR filter. | |

* \par | |

* <code>pCoeffs</code> points to a coefficient array of size <code>numTaps</code>. | |

* <code>numTaps</code> must be a multiple of the interpolation factor <code>L</code> and this is checked by the | |

* initialization functions. | |

* Internally, the function divides the FIR filter's impulse response into shorter filters of length | |

* <code>phaseLength=numTaps/L</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>blockSize + phaseLength - 1</code>. | |

* Samples in the state buffer are stored in the order: | |

* \par | |

* <pre> | |

* {x[n-phaseLength+1], x[n-phaseLength], x[n-phaseLength-1], x[n-phaseLength-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 length of the filter is a multiple of the interpolation factor. | |

* To do this manually without calling the init function, assign the follow subfields of the instance structure: | |

* L (interpolation factor), pCoeffs, phaseLength (numTaps / L), 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_interpolate_instance_f32 S = {L, phaseLength, pCoeffs, pState}; | |

* arm_fir_interpolate_instance_q31 S = {L, phaseLength, pCoeffs, pState}; | |

* arm_fir_interpolate_instance_q15 S = {L, phaseLength, pCoeffs, pState}; | |

* </pre> | |

* where <code>L</code> is the interpolation factor; <code>phaseLength=numTaps/L</code> is the | |

* length of each of the shorter FIR filters used internally, | |

* <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 interpolate 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_Interpolate | |

* @{ | |

*/ | |

/** | |

* @brief Processing function for the floating-point FIR interpolator. | |

* @param[in] *S points to an instance of the floating-point FIR interpolator 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. | |

*/ | |

#ifndef ARM_MATH_CM0_FAMILY | |

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

void arm_fir_interpolate_f32( | |

const arm_fir_interpolate_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 *ptr1, *ptr2; /* Temporary pointers for state and coefficient buffers */ | |

float32_t sum0; /* Accumulators */ | |

float32_t x0, c0; /* Temporary variables to hold state and coefficient values */ | |

uint32_t i, blkCnt, j; /* Loop counters */ | |

uint16_t phaseLen = S->phaseLength, tapCnt; /* Length of each polyphase filter component */ | |

float32_t acc0, acc1, acc2, acc3; | |

float32_t x1, x2, x3; | |

uint32_t blkCntN4; | |

float32_t c1, c2, c3; | |

/* S->pState buffer contains previous frame (phaseLen - 1) samples */ | |

/* pStateCurnt points to the location where the new input data should be written */ | |

pStateCurnt = S->pState + (phaseLen - 1u); | |

/* Initialise blkCnt */ | |

blkCnt = blockSize / 4; | |

blkCntN4 = blockSize - (4 * blkCnt); | |

/* Samples loop unrolled by 4 */ | |

while(blkCnt > 0u) | |

{ | |

/* Copy new input sample into the state buffer */ | |

*pStateCurnt++ = *pSrc++; | |

*pStateCurnt++ = *pSrc++; | |

*pStateCurnt++ = *pSrc++; | |

*pStateCurnt++ = *pSrc++; | |

/* Address modifier index of coefficient buffer */ | |

j = 1u; | |

/* Loop over the Interpolation factor. */ | |

i = (S->L); | |

while(i > 0u) | |

{ | |

/* Set accumulator to zero */ | |

acc0 = 0.0f; | |

acc1 = 0.0f; | |

acc2 = 0.0f; | |

acc3 = 0.0f; | |

/* Initialize state pointer */ | |

ptr1 = pState; | |

/* Initialize coefficient pointer */ | |

ptr2 = pCoeffs + (S->L - j); | |

/* Loop over the polyPhase length. Unroll by a factor of 4. | |

** Repeat until we've computed numTaps-(4*S->L) coefficients. */ | |

tapCnt = phaseLen >> 2u; | |

x0 = *(ptr1++); | |

x1 = *(ptr1++); | |

x2 = *(ptr1++); | |

while(tapCnt > 0u) | |

{ | |

/* Read the input sample */ | |

x3 = *(ptr1++); | |

/* Read the coefficient */ | |

c0 = *(ptr2); | |

/* Perform the multiply-accumulate */ | |

acc0 += x0 * c0; | |

acc1 += x1 * c0; | |

acc2 += x2 * c0; | |

acc3 += x3 * c0; | |

/* Read the coefficient */ | |

c1 = *(ptr2 + S->L); | |

/* Read the input sample */ | |

x0 = *(ptr1++); | |

/* Perform the multiply-accumulate */ | |

acc0 += x1 * c1; | |

acc1 += x2 * c1; | |

acc2 += x3 * c1; | |

acc3 += x0 * c1; | |

/* Read the coefficient */ | |

c2 = *(ptr2 + S->L * 2); | |

/* Read the input sample */ | |

x1 = *(ptr1++); | |

/* Perform the multiply-accumulate */ | |

acc0 += x2 * c2; | |

acc1 += x3 * c2; | |

acc2 += x0 * c2; | |

acc3 += x1 * c2; | |

/* Read the coefficient */ | |

c3 = *(ptr2 + S->L * 3); | |

/* Read the input sample */ | |

x2 = *(ptr1++); | |

/* Perform the multiply-accumulate */ | |

acc0 += x3 * c3; | |

acc1 += x0 * c3; | |

acc2 += x1 * c3; | |

acc3 += x2 * c3; | |

/* Upsampling is done by stuffing L-1 zeros between each sample. | |

* So instead of multiplying zeros with coefficients, | |

* Increment the coefficient pointer by interpolation factor times. */ | |

ptr2 += 4 * S->L; | |

/* Decrement the loop counter */ | |

tapCnt--; | |

} | |

/* If the polyPhase length is not a multiple of 4, compute the remaining filter taps */ | |

tapCnt = phaseLen % 0x4u; | |

while(tapCnt > 0u) | |

{ | |

/* Read the input sample */ | |

x3 = *(ptr1++); | |

/* Read the coefficient */ | |

c0 = *(ptr2); | |

/* Perform the multiply-accumulate */ | |

acc0 += x0 * c0; | |

acc1 += x1 * c0; | |

acc2 += x2 * c0; | |

acc3 += x3 * c0; | |

/* Increment the coefficient pointer by interpolation factor times. */ | |

ptr2 += S->L; | |

/* update states for next sample processing */ | |

x0 = x1; | |

x1 = x2; | |

x2 = x3; | |

/* Decrement the loop counter */ | |

tapCnt--; | |

} | |

/* The result is in the accumulator, store in the destination buffer. */ | |

*pDst = acc0; | |

*(pDst + S->L) = acc1; | |

*(pDst + 2 * S->L) = acc2; | |

*(pDst + 3 * S->L) = acc3; | |

pDst++; | |

/* Increment the address modifier index of coefficient buffer */ | |

j++; | |

/* Decrement the loop counter */ | |

i--; | |

} | |

/* Advance the state pointer by 1 | |

* to process the next group of interpolation factor number samples */ | |

pState = pState + 4; | |

pDst += S->L * 3; | |

/* Decrement the loop counter */ | |

blkCnt--; | |

} | |

/* If the blockSize is not a multiple of 4, compute any remaining output samples here. | |

** No loop unrolling is used. */ | |

while(blkCntN4 > 0u) | |

{ | |

/* Copy new input sample into the state buffer */ | |

*pStateCurnt++ = *pSrc++; | |

/* Address modifier index of coefficient buffer */ | |

j = 1u; | |

/* Loop over the Interpolation factor. */ | |

i = S->L; | |

while(i > 0u) | |

{ | |

/* Set accumulator to zero */ | |

sum0 = 0.0f; | |

/* Initialize state pointer */ | |

ptr1 = pState; | |

/* Initialize coefficient pointer */ | |

ptr2 = pCoeffs + (S->L - j); | |

/* Loop over the polyPhase length. Unroll by a factor of 4. | |

** Repeat until we've computed numTaps-(4*S->L) coefficients. */ | |

tapCnt = phaseLen >> 2u; | |

while(tapCnt > 0u) | |

{ | |

/* Read the coefficient */ | |

c0 = *(ptr2); | |

/* Upsampling is done by stuffing L-1 zeros between each sample. | |

* So instead of multiplying zeros with coefficients, | |

* Increment the coefficient pointer by interpolation factor times. */ | |

ptr2 += S->L; | |

/* Read the input sample */ | |

x0 = *(ptr1++); | |

/* Perform the multiply-accumulate */ | |

sum0 += x0 * c0; | |

/* Read the coefficient */ | |

c0 = *(ptr2); | |

/* Increment the coefficient pointer by interpolation factor times. */ | |

ptr2 += S->L; | |

/* Read the input sample */ | |

x0 = *(ptr1++); | |

/* Perform the multiply-accumulate */ | |

sum0 += x0 * c0; | |

/* Read the coefficient */ | |

c0 = *(ptr2); | |

/* Increment the coefficient pointer by interpolation factor times. */ | |

ptr2 += S->L; | |

/* Read the input sample */ | |

x0 = *(ptr1++); | |

/* Perform the multiply-accumulate */ | |

sum0 += x0 * c0; | |

/* Read the coefficient */ | |

c0 = *(ptr2); | |

/* Increment the coefficient pointer by interpolation factor times. */ | |

ptr2 += S->L; | |

/* Read the input sample */ | |

x0 = *(ptr1++); | |

/* Perform the multiply-accumulate */ | |

sum0 += x0 * c0; | |

/* Decrement the loop counter */ | |

tapCnt--; | |

} | |

/* If the polyPhase length is not a multiple of 4, compute the remaining filter taps */ | |

tapCnt = phaseLen % 0x4u; | |

while(tapCnt > 0u) | |

{ | |

/* Perform the multiply-accumulate */ | |

sum0 += *(ptr1++) * (*ptr2); | |

/* Increment the coefficient pointer by interpolation factor times. */ | |

ptr2 += S->L; | |

/* Decrement the loop counter */ | |

tapCnt--; | |

} | |

/* The result is in the accumulator, store in the destination buffer. */ | |

*pDst++ = sum0; | |

/* Increment the address modifier index of coefficient buffer */ | |

j++; | |

/* Decrement the loop counter */ | |

i--; | |

} | |

/* Advance the state pointer by 1 | |

* to process the next group of interpolation factor number samples */ | |

pState = pState + 1; | |

/* Decrement the loop counter */ | |

blkCntN4--; | |

} | |

/* Processing is complete. | |

** Now copy the last phaseLen - 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; | |

tapCnt = (phaseLen - 1u) >> 2u; | |

/* copy data */ | |

while(tapCnt > 0u) | |

{ | |

*pStateCurnt++ = *pState++; | |

*pStateCurnt++ = *pState++; | |

*pStateCurnt++ = *pState++; | |

*pStateCurnt++ = *pState++; | |

/* Decrement the loop counter */ | |

tapCnt--; | |

} | |

tapCnt = (phaseLen - 1u) % 0x04u; | |

/* copy data */ | |

while(tapCnt > 0u) | |

{ | |

*pStateCurnt++ = *pState++; | |

/* Decrement the loop counter */ | |

tapCnt--; | |

} | |

} | |

#else | |

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

void arm_fir_interpolate_f32( | |

const arm_fir_interpolate_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 *ptr1, *ptr2; /* Temporary pointers for state and coefficient buffers */ | |

float32_t sum; /* Accumulator */ | |

uint32_t i, blkCnt; /* Loop counters */ | |

uint16_t phaseLen = S->phaseLength, tapCnt; /* Length of each polyphase filter component */ | |

/* S->pState buffer contains previous frame (phaseLen - 1) samples */ | |

/* pStateCurnt points to the location where the new input data should be written */ | |

pStateCurnt = S->pState + (phaseLen - 1u); | |

/* Total number of intput samples */ | |

blkCnt = blockSize; | |

/* Loop over the blockSize. */ | |

while(blkCnt > 0u) | |

{ | |

/* Copy new input sample into the state buffer */ | |

*pStateCurnt++ = *pSrc++; | |

/* Loop over the Interpolation factor. */ | |

i = S->L; | |

while(i > 0u) | |

{ | |

/* Set accumulator to zero */ | |

sum = 0.0f; | |

/* Initialize state pointer */ | |

ptr1 = pState; | |

/* Initialize coefficient pointer */ | |

ptr2 = pCoeffs + (i - 1u); | |

/* Loop over the polyPhase length */ | |

tapCnt = phaseLen; | |

while(tapCnt > 0u) | |

{ | |

/* Perform the multiply-accumulate */ | |

sum += *ptr1++ * *ptr2; | |

/* Increment the coefficient pointer by interpolation factor times. */ | |

ptr2 += S->L; | |

/* Decrement the loop counter */ | |

tapCnt--; | |

} | |

/* The result is in the accumulator, store in the destination buffer. */ | |

*pDst++ = sum; | |

/* Decrement the loop counter */ | |

i--; | |

} | |

/* Advance the state pointer by 1 | |

* to process the next group of interpolation factor number samples */ | |

pState = pState + 1; | |

/* Decrement the loop counter */ | |

blkCnt--; | |

} | |

/* Processing is complete. | |

** Now copy the last phaseLen - 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; | |

tapCnt = phaseLen - 1u; | |

while(tapCnt > 0u) | |

{ | |

*pStateCurnt++ = *pState++; | |

/* Decrement the loop counter */ | |

tapCnt--; | |

} | |

} | |

#endif /* #ifndef ARM_MATH_CM0_FAMILY */ | |

/** | |

* @} end of FIR_Interpolate group | |

*/ |