00001 /* ---------------------------------------------------------------------- 00002 * Copyright (C) 2010 ARM Limited. All rights reserved. 00003 * 00004 * $Date: 15. July 2011 00005 * $Revision: V1.0.10 00006 * 00007 * Project: CMSIS DSP Library 00008 * Title: arm_fir_decimate_q31.c 00009 * 00010 * Description: Q31 FIR Decimator. 00011 * 00012 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0 00013 * 00014 * Version 1.0.10 2011/7/15 00015 * Big Endian support added and Merged M0 and M3/M4 Source code. 00016 * 00017 * Version 1.0.3 2010/11/29 00018 * Re-organized the CMSIS folders and updated documentation. 00019 * 00020 * Version 1.0.2 2010/11/11 00021 * Documentation updated. 00022 * 00023 * Version 1.0.1 2010/10/05 00024 * Production release and review comments incorporated. 00025 * 00026 * Version 1.0.0 2010/09/20 00027 * Production release and review comments incorporated 00028 * 00029 * Version 0.0.7 2010/06/10 00030 * Misra-C changes done 00031 * -------------------------------------------------------------------- */ 00032 00033 #include "arm_math.h" 00034 00064 void arm_fir_decimate_q31( 00065 const arm_fir_decimate_instance_q31 * S, 00066 q31_t * pSrc, 00067 q31_t * pDst, 00068 uint32_t blockSize) 00069 { 00070 q31_t *pState = S->pState; /* State pointer */ 00071 q31_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ 00072 q31_t *pStateCurnt; /* Points to the current sample of the state */ 00073 q31_t x0, c0; /* Temporary variables to hold state and coefficient values */ 00074 q31_t *px; /* Temporary pointers for state buffer */ 00075 q31_t *pb; /* Temporary pointers for coefficient buffer */ 00076 q63_t sum0; /* Accumulator */ 00077 uint32_t numTaps = S->numTaps; /* Number of taps */ 00078 uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M; /* Loop counters */ 00079 00080 00081 #ifndef ARM_MATH_CM0 00082 00083 /* Run the below code for Cortex-M4 and Cortex-M3 */ 00084 00085 /* S->pState buffer contains previous frame (numTaps - 1) samples */ 00086 /* pStateCurnt points to the location where the new input data should be written */ 00087 pStateCurnt = S->pState + (numTaps - 1u); 00088 00089 /* Total number of output samples to be computed */ 00090 blkCnt = outBlockSize; 00091 00092 while(blkCnt > 0u) 00093 { 00094 /* Copy decimation factor number of new input samples into the state buffer */ 00095 i = S->M; 00096 00097 do 00098 { 00099 *pStateCurnt++ = *pSrc++; 00100 00101 } while(--i); 00102 00103 /* Set accumulator to zero */ 00104 sum0 = 0; 00105 00106 /* Initialize state pointer */ 00107 px = pState; 00108 00109 /* Initialize coeff pointer */ 00110 pb = pCoeffs; 00111 00112 /* Loop unrolling. Process 4 taps at a time. */ 00113 tapCnt = numTaps >> 2; 00114 00115 /* Loop over the number of taps. Unroll by a factor of 4. 00116 ** Repeat until we've computed numTaps-4 coefficients. */ 00117 while(tapCnt > 0u) 00118 { 00119 /* Read the b[numTaps-1] coefficient */ 00120 c0 = *(pb++); 00121 00122 /* Read x[n-numTaps-1] sample */ 00123 x0 = *(px++); 00124 00125 /* Perform the multiply-accumulate */ 00126 sum0 += (q63_t) x0 *c0; 00127 00128 /* Read the b[numTaps-2] coefficient */ 00129 c0 = *(pb++); 00130 00131 /* Read x[n-numTaps-2] sample */ 00132 x0 = *(px++); 00133 00134 /* Perform the multiply-accumulate */ 00135 sum0 += (q63_t) x0 *c0; 00136 00137 /* Read the b[numTaps-3] coefficient */ 00138 c0 = *(pb++); 00139 00140 /* Read x[n-numTaps-3] sample */ 00141 x0 = *(px++); 00142 00143 /* Perform the multiply-accumulate */ 00144 sum0 += (q63_t) x0 *c0; 00145 00146 /* Read the b[numTaps-4] coefficient */ 00147 c0 = *(pb++); 00148 00149 /* Read x[n-numTaps-4] sample */ 00150 x0 = *(px++); 00151 00152 /* Perform the multiply-accumulate */ 00153 sum0 += (q63_t) x0 *c0; 00154 00155 /* Decrement the loop counter */ 00156 tapCnt--; 00157 } 00158 00159 /* If the filter length is not a multiple of 4, compute the remaining filter taps */ 00160 tapCnt = numTaps % 0x4u; 00161 00162 while(tapCnt > 0u) 00163 { 00164 /* Read coefficients */ 00165 c0 = *(pb++); 00166 00167 /* Fetch 1 state variable */ 00168 x0 = *(px++); 00169 00170 /* Perform the multiply-accumulate */ 00171 sum0 += (q63_t) x0 *c0; 00172 00173 /* Decrement the loop counter */ 00174 tapCnt--; 00175 } 00176 00177 /* Advance the state pointer by the decimation factor 00178 * to process the next group of decimation factor number samples */ 00179 pState = pState + S->M; 00180 00181 /* The result is in the accumulator, store in the destination buffer. */ 00182 *pDst++ = (q31_t) (sum0 >> 31); 00183 00184 /* Decrement the loop counter */ 00185 blkCnt--; 00186 } 00187 00188 /* Processing is complete. 00189 ** Now copy the last numTaps - 1 samples to the satrt of the state buffer. 00190 ** This prepares the state buffer for the next function call. */ 00191 00192 /* Points to the start of the state buffer */ 00193 pStateCurnt = S->pState; 00194 00195 i = (numTaps - 1u) >> 2u; 00196 00197 /* copy data */ 00198 while(i > 0u) 00199 { 00200 *pStateCurnt++ = *pState++; 00201 *pStateCurnt++ = *pState++; 00202 *pStateCurnt++ = *pState++; 00203 *pStateCurnt++ = *pState++; 00204 00205 /* Decrement the loop counter */ 00206 i--; 00207 } 00208 00209 i = (numTaps - 1u) % 0x04u; 00210 00211 /* copy data */ 00212 while(i > 0u) 00213 { 00214 *pStateCurnt++ = *pState++; 00215 00216 /* Decrement the loop counter */ 00217 i--; 00218 } 00219 00220 #else 00221 00222 /* Run the below code for Cortex-M0 */ 00223 00224 /* S->pState buffer contains previous frame (numTaps - 1) samples */ 00225 /* pStateCurnt points to the location where the new input data should be written */ 00226 pStateCurnt = S->pState + (numTaps - 1u); 00227 00228 /* Total number of output samples to be computed */ 00229 blkCnt = outBlockSize; 00230 00231 while(blkCnt > 0u) 00232 { 00233 /* Copy decimation factor number of new input samples into the state buffer */ 00234 i = S->M; 00235 00236 do 00237 { 00238 *pStateCurnt++ = *pSrc++; 00239 00240 } while(--i); 00241 00242 /* Set accumulator to zero */ 00243 sum0 = 0; 00244 00245 /* Initialize state pointer */ 00246 px = pState; 00247 00248 /* Initialize coeff pointer */ 00249 pb = pCoeffs; 00250 00251 tapCnt = numTaps; 00252 00253 while(tapCnt > 0u) 00254 { 00255 /* Read coefficients */ 00256 c0 = *pb++; 00257 00258 /* Fetch 1 state variable */ 00259 x0 = *px++; 00260 00261 /* Perform the multiply-accumulate */ 00262 sum0 += (q63_t) x0 *c0; 00263 00264 /* Decrement the loop counter */ 00265 tapCnt--; 00266 } 00267 00268 /* Advance the state pointer by the decimation factor 00269 * to process the next group of decimation factor number samples */ 00270 pState = pState + S->M; 00271 00272 /* The result is in the accumulator, store in the destination buffer. */ 00273 *pDst++ = (q31_t) (sum0 >> 31); 00274 00275 /* Decrement the loop counter */ 00276 blkCnt--; 00277 } 00278 00279 /* Processing is complete. 00280 ** Now copy the last numTaps - 1 samples to the start of the state buffer. 00281 ** This prepares the state buffer for the next function call. */ 00282 00283 /* Points to the start of the state buffer */ 00284 pStateCurnt = S->pState; 00285 00286 i = numTaps - 1u; 00287 00288 /* copy data */ 00289 while(i > 0u) 00290 { 00291 *pStateCurnt++ = *pState++; 00292 00293 /* Decrement the loop counter */ 00294 i--; 00295 } 00296 00297 #endif /* #ifndef ARM_MATH_CM0 */ 00298 00299 } 00300