- Main Page
- Modules
- Data Structures
- Files
- Examples

- File List
- Globals

# arm_fir_fast_q15.c

Go to the documentation of this file.

    00001 /* ----------------------------------------------------------------------
    00002 * Copyright (C) 2010 ARM Limited. All rights reserved.
    00003 *
    00004 * $Date:        29. November 2010
    00005 * $Revision:    V1.0.3
    00006 *
    00007 * Project:      CMSIS DSP Library
    00008 * Title:        arm_fir_fast_q15.c
    00009 *
    00010 * Description:  Q15 Fast FIR filter processing function.
    00011 *
    00012 * Target Processor: Cortex-M4/Cortex-M3
    00013 *
    00014 * Version 1.0.3 2010/11/29
    00015 *    Re-organized the CMSIS folders and updated documentation.
    00016 *
    00017 * Version 1.0.2 2010/11/11
    00018 *    Documentation updated.
    00019 *
    00020 * Version 1.0.1 2010/10/05
    00021 *    Production release and review comments incorporated.
    00022 *
    00023 * Version 1.0.0 2010/09/20
    00024 *    Production release and review comments incorporated.
    00025 *
    00026 * Version 0.0.9  2010/08/16
    00027 *    Initial version
    00028 *
    00029 * -------------------------------------------------------------------- */
    00030
    00031 #include "arm_math.h"
    00032
    00062 void arm_fir_fast_q15(
    00063   const arm_fir_instance_q15 * S,
    00064   q15_t * pSrc,
    00065   q15_t * pDst,
    00066   uint32_t blockSize)
    00067 {
    00068   q15_t *pState = S->pState;                     /* State pointer */
    00069   q15_t *pCoeffs = S->pCoeffs;                   /* Coefficient pointer */
    00070   q15_t *pStateCurnt;                            /* Points to the current sample of the state */
    00071   q15_t *px1;                                    /* Temporary q15 pointer for state buffer */
    00072   q31_t *pb;                                     /* Temporary pointer for coefficient buffer */
    00073   q31_t *px2;                                    /* Temporary q31 pointer for SIMD state buffer accesses */
    00074   q31_t x0, x1, x2, x3, c0;                      /* Temporary variables to hold SIMD state and coefficient values */
    00075   q31_t acc0, acc1, acc2, acc3;                  /* Accumulators */
    00076   uint32_t numTaps = S->numTaps;                 /* Number of taps in the filter */
    00077   uint32_t tapCnt, blkCnt;                       /* Loop counters */
    00078
    00079   /* S->pState points to buffer which contains previous frame (numTaps - 1) samples */
    00080   /* pStateCurnt points to the location where the new input data should be written */
    00081   pStateCurnt = &(S->pState[(numTaps - 1u)]);
    00082
    00083   /* Apply loop unrolling and compute 4 output values simultaneously.
    00084    * The variables acc0 ... acc3 hold output values that are being computed:
    00085    *
    00086    *    acc0 =  b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0]
    00087    *    acc1 =  b[numTaps-1] * x[n-numTaps] +   b[numTaps-2] * x[n-numTaps-1] + b[numTaps-3] * x[n-numTaps-2] +...+ b[0] * x[1]
    00088    *    acc2 =  b[numTaps-1] * x[n-numTaps+1] + b[numTaps-2] * x[n-numTaps] +   b[numTaps-3] * x[n-numTaps-1] +...+ b[0] * x[2]
    00089    *    acc3 =  b[numTaps-1] * x[n-numTaps+2] + b[numTaps-2] * x[n-numTaps+1] + b[numTaps-3] * x[n-numTaps]   +...+ b[0] * x[3]
    00090    */
    00091   blkCnt = blockSize >> 2;
    00092
    00093   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00094    ** a second loop below computes the remaining 1 to 3 samples. */
    00095   while(blkCnt > 0u)
    00096   {
    00097     /* Copy four new input samples into the state buffer.
    00098      ** Use 32-bit SIMD to move the 16-bit data.  Only requires two copies. */
    00099     *__SIMD32(pStateCurnt)++ = *__SIMD32(pSrc)++;
    00100     *__SIMD32(pStateCurnt)++ = *__SIMD32(pSrc)++;
    00101
    00102     /* Set all accumulators to zero */
    00103     acc0 = 0;
    00104     acc1 = 0;
    00105     acc2 = 0;
    00106     acc3 = 0;
    00107
    00108     /* Initialize state pointer of type q15 */
    00109     px1 = pState;
    00110
    00111     /* Initialize coeff pointer of type q31 */
    00112     pb = (q31_t *) (pCoeffs);
    00113
    00114     /* Read the first two samples from the state buffer:  x[n-N], x[n-N-1] */
    00115     x0 = *(q31_t *) (px1++);
    00116
    00117     /* Read the third and forth samples from the state buffer: x[n-N-1], x[n-N-2] */
    00118     x1 = *(q31_t *) (px1++);
    00119
    00120     /* Loop over the number of taps.  Unroll by a factor of 4.
    00121      ** Repeat until we've computed numTaps-4 coefficients. */
    00122     tapCnt = numTaps >> 2;
    00123     do
    00124     {
    00125       /* Read the first two coefficients using SIMD:  b[N] and b[N-1] coefficients */
    00126       c0 = *(pb++);
    00127
    00128       /* acc0 +=  b[N] * x[n-N] + b[N-1] * x[n-N-1] */
    00129       acc0 = __SMLAD(x0, c0, acc0);
    00130
    00131       /* acc1 +=  b[N] * x[n-N-1] + b[N-1] * x[n-N-2] */
    00132       acc1 = __SMLAD(x1, c0, acc1);
    00133
    00134       /* Read state x[n-N-2], x[n-N-3] */
    00135       x2 = *(q31_t *) (px1++);
    00136
    00137       /* Read state x[n-N-3], x[n-N-4] */
    00138       x3 = *(q31_t *) (px1++);
    00139
    00140       /* acc2 +=  b[N] * x[n-N-2] + b[N-1] * x[n-N-3] */
    00141       acc2 = __SMLAD(x2, c0, acc2);
    00142
    00143       /* acc3 +=  b[N] * x[n-N-3] + b[N-1] * x[n-N-4] */
    00144       acc3 = __SMLAD(x3, c0, acc3);
    00145
    00146       /* Read coefficients b[N-2], b[N-3] */
    00147       c0 = *(pb++);
    00148
    00149       /* acc0 +=  b[N-2] * x[n-N-2] + b[N-3] * x[n-N-3] */
    00150       acc0 = __SMLAD(x2, c0, acc0);
    00151
    00152       /* acc1 +=  b[N-2] * x[n-N-3] + b[N-3] * x[n-N-4] */
    00153       acc1 = __SMLAD(x3, c0, acc1);
    00154
    00155       /* Read state x[n-N-4], x[n-N-5] */
    00156       x0 = *(q31_t *) (px1++);
    00157
    00158       /* Read state x[n-N-5], x[n-N-6] */
    00159       x1 = *(q31_t *) (px1++);
    00160
    00161       /* acc2 +=  b[N-2] * x[n-N-4] + b[N-3] * x[n-N-5] */
    00162       acc2 = __SMLAD(x0, c0, acc2);
    00163
    00164       /* acc3 +=  b[N-2] * x[n-N-5] + b[N-3] * x[n-N-6] */
    00165       acc3 = __SMLAD(x1, c0, acc3);
    00166       tapCnt--;
    00167
    00168     }
    00169     while(tapCnt > 0u);
    00170
    00171     /* If the filter length is not a multiple of 4, compute the remaining filter taps.
    00172      ** This is always 2 taps since the filter length is always even. */
    00173     if((numTaps & 0x3u) != 0u)
    00174     {
    00175       /* Read 2 coefficients */
    00176       c0 = *(pb++);
    00177       /* Fetch 4 state variables */
    00178       x2 = *(q31_t *) (px1++);
    00179       x3 = *(q31_t *) (px1++);
    00180
    00181       /* Perform the multiply-accumulates */
    00182       acc0 = __SMLAD(x0, c0, acc0);
    00183       acc1 = __SMLAD(x1, c0, acc1);
    00184       acc2 = __SMLAD(x2, c0, acc2);
    00185       acc3 = __SMLAD(x3, c0, acc3);
    00186     }
    00187
    00188     /* The results in the 4 accumulators are in 2.30 format.  Convert to 1.15 with saturation.
    00189      ** Then store the 4 outputs in the destination buffer. */
    00190     *__SIMD32(pDst)++ = __PKHBT((acc0 >> 15), (acc1 >> 15), 16u);
    00191     *__SIMD32(pDst)++ = __PKHBT((acc2 >> 15), (acc3 >> 15), 16u);
    00192
    00193
    00194     /* Advance the state pointer by 4 to process the next group of 4 samples */
    00195     pState = pState + 4;
    00196
    00197     /* Decrement the loop counter */
    00198     blkCnt--;
    00199   }
    00200
    00201   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00202    ** No loop unrolling is used. */
    00203   blkCnt = blockSize % 0x4u;
    00204   while(blkCnt > 0u)
    00205   {
    00206     /* Copy two samples into state buffer */
    00207     *pStateCurnt++ = *pSrc++;
    00208
    00209     /* Set the accumulator to zero */
    00210     acc0 = 0;
    00211
    00212     /* Use SIMD to hold states and coefficients */
    00213     px2 = (q31_t *) pState;
    00214     pb = (q31_t *) (pCoeffs);
    00215     tapCnt = numTaps >> 1;
    00216
    00217     do
    00218     {
    00219       acc0 = __SMLAD(*px2++, *(pb++), acc0);
    00220       tapCnt--;
    00221     }
    00222     while(tapCnt > 0u);
    00223
    00224     /* The result is in 2.30 format.  Convert to 1.15 with saturation.
    00225      ** Then store the output in the destination buffer. */
    00226     *pDst++ = (q15_t) ((acc0 >> 15));
    00227
    00228     /* Advance state pointer by 1 for the next sample */
    00229     pState = pState + 1;
    00230
    00231     /* Decrement the loop counter */
    00232     blkCnt--;
    00233   }
    00234
    00235   /* Processing is complete.
    00236    ** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
    00237    ** This prepares the state buffer for the next function call. */
    00238
    00239   /* Points to the start of the state buffer */
    00240   pStateCurnt = S->pState;
    00241   /* Calculation of count for copying integer writes */
    00242   tapCnt = (numTaps - 1u) >> 2;
    00243
    00244   while(tapCnt > 0u)
    00245   {
    00246     *__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++;
    00247     *__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++;
    00248
    00249     tapCnt--;
    00250   }
    00251
    00252   /* Calculation of count for remaining q15_t data */
    00253   tapCnt = (numTaps - 1u) % 0x4u;
    00254
    00255   /* copy remaining data */
    00256   while(tapCnt > 0u)
    00257   {
    00258     *pStateCurnt++ = *pState++;
    00259
    00260     /* Decrement the loop counter */
    00261     tapCnt--;
    00262   }
    00263 }
    00264

All Data Structures Files Functions Variables Typedefs Enumerations Enumerator Defines