| /* ---------------------------------------------------------------------- |
| * Copyright (C) 2010 ARM Limited. All rights reserved. |
| * |
| * $Date: 15. July 2011 |
| * $Revision: V1.0.10 |
| * |
| * Project: CMSIS DSP Library |
| * Title: arm_fir_decimate_fast_q31.c |
| * |
| * Description: Fast Q31 FIR Decimator. |
| * |
| * Target Processor: Cortex-M4/Cortex-M3 |
| * |
| * Version 1.0.10 2011/7/15 |
| * Big Endian support added and Merged M0 and M3/M4 Source code. |
| * |
| * Version 1.0.3 2010/11/29 |
| * Re-organized the CMSIS folders and updated documentation. |
| * |
| * Version 1.0.2 2010/11/11 |
| * Documentation updated. |
| * |
| * Version 1.0.1 2010/10/05 |
| * Production release and review comments incorporated. |
| * |
| * Version 1.0.0 2010/09/20 |
| * Production release and review comments incorporated. |
| * -------------------------------------------------------------------- */ |
| |
| #include "arm_math.h" |
| |
| /** |
| * @ingroup groupFilters |
| */ |
| |
| /** |
| * @addtogroup FIR_decimate |
| * @{ |
| */ |
| |
| /** |
| * @brief Processing function for the Q31 FIR decimator (fast variant) for Cortex-M3 and Cortex-M4. |
| * @param[in] *S points to an instance of the Q31 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 |
| * |
| * <b>Scaling and Overflow Behavior:</b> |
| * |
| * \par |
| * This function is optimized for speed at the expense of fixed-point precision and overflow protection. |
| * The result of each 1.31 x 1.31 multiplication is truncated to 2.30 format. |
| * These intermediate results are added to a 2.30 accumulator. |
| * Finally, the accumulator is saturated and converted to a 1.31 result. |
| * The fast version has the same overflow behavior as the standard version and provides less precision since it discards the low 32 bits of each multiplication result. |
| * In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits (where log2 is read as log to the base 2). |
| * |
| * \par |
| * Refer to the function <code>arm_fir_decimate_q31()</code> for a slower implementation of this function which uses a 64-bit accumulator to provide higher precision. |
| * Both the slow and the fast versions use the same instance structure. |
| * Use the function <code>arm_fir_decimate_init_q31()</code> to initialize the filter structure. |
| */ |
| |
| void arm_fir_decimate_fast_q31( |
| arm_fir_decimate_instance_q31 * S, |
| q31_t * pSrc, |
| q31_t * pDst, |
| uint32_t blockSize) |
| { |
| q31_t *pState = S->pState; /* State pointer */ |
| q31_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ |
| q31_t *pStateCurnt; /* Points to the current sample of the state */ |
| q31_t x0, c0; /* Temporary variables to hold state and coefficient values */ |
| q31_t *px; /* Temporary pointers for state buffer */ |
| q31_t *pb; /* Temporary pointers for coefficient buffer */ |
| q63_t sum0; /* Accumulator */ |
| uint32_t numTaps = S->numTaps; /* Number of taps */ |
| uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M; /* Loop counters */ |
| |
| |
| /* 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; |
| |
| /* 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 = (q31_t) ((((q63_t) x0 * c0) + (sum0 << 32)) >> 32); |
| |
| /* Read the b[numTaps-2] coefficient */ |
| c0 = *(pb++); |
| |
| /* Read x[n-numTaps-2] sample */ |
| x0 = *(px++); |
| |
| /* Perform the multiply-accumulate */ |
| sum0 = (q31_t) ((((q63_t) x0 * c0) + (sum0 << 32)) >> 32); |
| |
| /* Read the b[numTaps-3] coefficient */ |
| c0 = *(pb++); |
| |
| /* Read x[n-numTaps-3] sample */ |
| x0 = *(px++); |
| |
| /* Perform the multiply-accumulate */ |
| sum0 = (q31_t) ((((q63_t) x0 * c0) + (sum0 << 32)) >> 32); |
| |
| /* Read the b[numTaps-4] coefficient */ |
| c0 = *(pb++); |
| |
| /* Read x[n-numTaps-4] sample */ |
| x0 = *(px++); |
| |
| /* Perform the multiply-accumulate */ |
| sum0 = (q31_t) ((((q63_t) x0 * c0) + (sum0 << 32)) >> 32); |
| |
| /* 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 = (q31_t) ((((q63_t) x0 * c0) + (sum0 << 32)) >> 32); |
| |
| /* 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++ = (q31_t) (sum0 << 1); |
| |
| /* Decrement the loop counter */ |
| blkCnt--; |
| } |
| |
| /* 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) >> 2u; |
| |
| /* 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--; |
| } |
| } |
| |
| /** |
| * @} end of FIR_decimate group |
| */ |