CMSIS DSP library
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arm_biquad_cascade_df1_32x64_q31.c
00001 /* ---------------------------------------------------------------------- 00002 * Copyright (C) 2010-2013 ARM Limited. All rights reserved. 00003 * 00004 * $Date: 17. January 2013 00005 * $Revision: V1.4.1 00006 * 00007 * Project: CMSIS DSP Library 00008 * Title: arm_biquad_cascade_df1_32x64_q31.c 00009 * 00010 * Description: High precision Q31 Biquad cascade filter processing function 00011 * 00012 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0 00013 * 00014 * Redistribution and use in source and binary forms, with or without 00015 * modification, are permitted provided that the following conditions 00016 * are met: 00017 * - Redistributions of source code must retain the above copyright 00018 * notice, this list of conditions and the following disclaimer. 00019 * - Redistributions in binary form must reproduce the above copyright 00020 * notice, this list of conditions and the following disclaimer in 00021 * the documentation and/or other materials provided with the 00022 * distribution. 00023 * - Neither the name of ARM LIMITED nor the names of its contributors 00024 * may be used to endorse or promote products derived from this 00025 * software without specific prior written permission. 00026 * 00027 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 00028 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 00029 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 00030 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 00031 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 00032 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 00033 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 00034 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 00035 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 00036 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 00037 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 00038 * POSSIBILITY OF SUCH DAMAGE. 00039 * -------------------------------------------------------------------- */ 00040 00041 #include "arm_math.h" 00042 00043 /** 00044 * @ingroup groupFilters 00045 */ 00046 00047 /** 00048 * @defgroup BiquadCascadeDF1_32x64 High Precision Q31 Biquad Cascade Filter 00049 * 00050 * This function implements a high precision Biquad cascade filter which operates on 00051 * Q31 data values. The filter coefficients are in 1.31 format and the state variables 00052 * are in 1.63 format. The double precision state variables reduce quantization noise 00053 * in the filter and provide a cleaner output. 00054 * These filters are particularly useful when implementing filters in which the 00055 * singularities are close to the unit circle. This is common for low pass or high 00056 * pass filters with very low cutoff frequencies. 00057 * 00058 * The function operates on blocks of input and output data 00059 * and each call to the function processes <code>blockSize</code> samples through 00060 * the filter. <code>pSrc</code> and <code>pDst</code> points to input and output arrays 00061 * containing <code>blockSize</code> Q31 values. 00062 * 00063 * \par Algorithm 00064 * Each Biquad stage implements a second order filter using the difference equation: 00065 * <pre> 00066 * y[n] = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] 00067 * </pre> 00068 * A Direct Form I algorithm is used with 5 coefficients and 4 state variables per stage. 00069 * \image html Biquad.gif "Single Biquad filter stage" 00070 * Coefficients <code>b0, b1, and b2 </code> multiply the input signal <code>x[n]</code> and are referred to as the feedforward coefficients. 00071 * Coefficients <code>a1</code> and <code>a2</code> multiply the output signal <code>y[n]</code> and are referred to as the feedback coefficients. 00072 * Pay careful attention to the sign of the feedback coefficients. 00073 * Some design tools use the difference equation 00074 * <pre> 00075 * y[n] = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] - a1 * y[n-1] - a2 * y[n-2] 00076 * </pre> 00077 * In this case the feedback coefficients <code>a1</code> and <code>a2</code> must be negated when used with the CMSIS DSP Library. 00078 * 00079 * \par 00080 * Higher order filters are realized as a cascade of second order sections. 00081 * <code>numStages</code> refers to the number of second order stages used. 00082 * For example, an 8th order filter would be realized with <code>numStages=4</code> second order stages. 00083 * \image html BiquadCascade.gif "8th order filter using a cascade of Biquad stages" 00084 * A 9th order filter would be realized with <code>numStages=5</code> second order stages with the coefficients for one of the stages configured as a first order filter (<code>b2=0</code> and <code>a2=0</code>). 00085 * 00086 * \par 00087 * The <code>pState</code> points to state variables array . 00088 * Each Biquad stage has 4 state variables <code>x[n-1], x[n-2], y[n-1],</code> and <code>y[n-2]</code> and each state variable in 1.63 format to improve precision. 00089 * The state variables are arranged in the array as: 00090 * <pre> 00091 * {x[n-1], x[n-2], y[n-1], y[n-2]} 00092 * </pre> 00093 * 00094 * \par 00095 * The 4 state variables for stage 1 are first, then the 4 state variables for stage 2, and so on. 00096 * The state array has a total length of <code>4*numStages</code> values of data in 1.63 format. 00097 * The state variables are updated after each block of data is processed; the coefficients are untouched. 00098 * 00099 * \par Instance Structure 00100 * The coefficients and state variables for a filter are stored together in an instance data structure. 00101 * A separate instance structure must be defined for each filter. 00102 * Coefficient arrays may be shared among several instances while state variable arrays cannot be shared. 00103 * 00104 * \par Init Function 00105 * There is also an associated initialization function which performs the following operations: 00106 * - Sets the values of the internal structure fields. 00107 * - Zeros out the values in the state buffer. 00108 * To do this manually without calling the init function, assign the follow subfields of the instance structure: 00109 * numStages, pCoeffs, postShift, pState. Also set all of the values in pState to zero. 00110 * 00111 * \par 00112 * Use of the initialization function is optional. 00113 * However, if the initialization function is used, then the instance structure cannot be placed into a const data section. 00114 * To place an instance structure into a const data section, the instance structure must be manually initialized. 00115 * Set the values in the state buffer to zeros before static initialization. 00116 * For example, to statically initialize the filter instance structure use 00117 * <pre> 00118 * arm_biquad_cas_df1_32x64_ins_q31 S1 = {numStages, pState, pCoeffs, postShift}; 00119 * </pre> 00120 * where <code>numStages</code> is the number of Biquad stages in the filter; <code>pState</code> is the address of the state buffer; 00121 * <code>pCoeffs</code> is the address of the coefficient buffer; <code>postShift</code> shift to be applied which is described in detail below. 00122 * \par Fixed-Point Behavior 00123 * Care must be taken while using Biquad Cascade 32x64 filter function. 00124 * Following issues must be considered: 00125 * - Scaling of coefficients 00126 * - Filter gain 00127 * - Overflow and saturation 00128 * 00129 * \par 00130 * Filter coefficients are represented as fractional values and 00131 * restricted to lie in the range <code>[-1 +1)</code>. 00132 * The processing function has an additional scaling parameter <code>postShift</code> 00133 * which allows the filter coefficients to exceed the range <code>[+1 -1)</code>. 00134 * At the output of the filter's accumulator is a shift register which shifts the result by <code>postShift</code> bits. 00135 * \image html BiquadPostshift.gif "Fixed-point Biquad with shift by postShift bits after accumulator" 00136 * This essentially scales the filter coefficients by <code>2^postShift</code>. 00137 * For example, to realize the coefficients 00138 * <pre> 00139 * {1.5, -0.8, 1.2, 1.6, -0.9} 00140 * </pre> 00141 * set the Coefficient array to: 00142 * <pre> 00143 * {0.75, -0.4, 0.6, 0.8, -0.45} 00144 * </pre> 00145 * and set <code>postShift=1</code> 00146 * 00147 * \par 00148 * The second thing to keep in mind is the gain through the filter. 00149 * The frequency response of a Biquad filter is a function of its coefficients. 00150 * It is possible for the gain through the filter to exceed 1.0 meaning that the filter increases the amplitude of certain frequencies. 00151 * This means that an input signal with amplitude < 1.0 may result in an output > 1.0 and these are saturated or overflowed based on the implementation of the filter. 00152 * To avoid this behavior the filter needs to be scaled down such that its peak gain < 1.0 or the input signal must be scaled down so that the combination of input and filter are never overflowed. 00153 * 00154 * \par 00155 * The third item to consider is the overflow and saturation behavior of the fixed-point Q31 version. 00156 * This is described in the function specific documentation below. 00157 */ 00158 00159 /** 00160 * @addtogroup BiquadCascadeDF1_32x64 00161 * @{ 00162 */ 00163 00164 /** 00165 * @details 00166 00167 * @param[in] *S points to an instance of the high precision Q31 Biquad cascade filter. 00168 * @param[in] *pSrc points to the block of input data. 00169 * @param[out] *pDst points to the block of output data. 00170 * @param[in] blockSize number of samples to process. 00171 * @return none. 00172 * 00173 * \par 00174 * The function is implemented using an internal 64-bit accumulator. 00175 * The accumulator has a 2.62 format and maintains full precision of the intermediate multiplication results but provides only a single guard bit. 00176 * Thus, if the accumulator result overflows it wraps around rather than clip. 00177 * In order to avoid overflows completely the input signal must be scaled down by 2 bits and lie in the range [-0.25 +0.25). 00178 * After all 5 multiply-accumulates are performed, the 2.62 accumulator is shifted by <code>postShift</code> bits and the result truncated to 00179 * 1.31 format by discarding the low 32 bits. 00180 * 00181 * \par 00182 * Two related functions are provided in the CMSIS DSP library. 00183 * <code>arm_biquad_cascade_df1_q31()</code> implements a Biquad cascade with 32-bit coefficients and state variables with a Q63 accumulator. 00184 * <code>arm_biquad_cascade_df1_fast_q31()</code> implements a Biquad cascade with 32-bit coefficients and state variables with a Q31 accumulator. 00185 */ 00186 00187 void arm_biquad_cas_df1_32x64_q31 ( 00188 const arm_biquad_cas_df1_32x64_ins_q31 * S, 00189 q31_t * pSrc, 00190 q31_t * pDst, 00191 uint32_t blockSize) 00192 { 00193 q31_t *pIn = pSrc; /* input pointer initialization */ 00194 q31_t *pOut = pDst; /* output pointer initialization */ 00195 q63_t *pState = S->pState; /* state pointer initialization */ 00196 q31_t *pCoeffs = S->pCoeffs; /* coeff pointer initialization */ 00197 q63_t acc; /* accumulator */ 00198 q31_t Xn1, Xn2; /* Input Filter state variables */ 00199 q63_t Yn1, Yn2; /* Output Filter state variables */ 00200 q31_t b0, b1, b2, a1, a2; /* Filter coefficients */ 00201 q31_t Xn; /* temporary input */ 00202 int32_t shift = (int32_t) S->postShift + 1; /* Shift to be applied to the output */ 00203 uint32_t sample, stage = S->numStages; /* loop counters */ 00204 q31_t acc_l, acc_h; /* temporary output */ 00205 uint32_t uShift = ((uint32_t) S->postShift + 1u); 00206 uint32_t lShift = 32u - uShift; /* Shift to be applied to the output */ 00207 00208 00209 #ifndef ARM_MATH_CM0_FAMILY 00210 00211 /* Run the below code for Cortex-M4 and Cortex-M3 */ 00212 00213 do 00214 { 00215 /* Reading the coefficients */ 00216 b0 = *pCoeffs++; 00217 b1 = *pCoeffs++; 00218 b2 = *pCoeffs++; 00219 a1 = *pCoeffs++; 00220 a2 = *pCoeffs++; 00221 00222 /* Reading the state values */ 00223 Xn1 = (q31_t) (pState[0]); 00224 Xn2 = (q31_t) (pState[1]); 00225 Yn1 = pState[2]; 00226 Yn2 = pState[3]; 00227 00228 /* Apply loop unrolling and compute 4 output values simultaneously. */ 00229 /* The variable acc hold output value that is being computed and 00230 * stored in the destination buffer 00231 * acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] 00232 */ 00233 00234 sample = blockSize >> 2u; 00235 00236 /* First part of the processing with loop unrolling. Compute 4 outputs at a time. 00237 ** a second loop below computes the remaining 1 to 3 samples. */ 00238 while(sample > 0u) 00239 { 00240 /* Read the input */ 00241 Xn = *pIn++; 00242 00243 /* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ 00244 00245 /* acc = b0 * x[n] */ 00246 acc = (q63_t) Xn *b0; 00247 00248 /* acc += b1 * x[n-1] */ 00249 acc += (q63_t) Xn1 *b1; 00250 00251 /* acc += b[2] * x[n-2] */ 00252 acc += (q63_t) Xn2 *b2; 00253 00254 /* acc += a1 * y[n-1] */ 00255 acc += mult32x64(Yn1, a1); 00256 00257 /* acc += a2 * y[n-2] */ 00258 acc += mult32x64(Yn2, a2); 00259 00260 /* The result is converted to 1.63 , Yn2 variable is reused */ 00261 Yn2 = acc << shift; 00262 00263 /* Calc lower part of acc */ 00264 acc_l = acc & 0xffffffff; 00265 00266 /* Calc upper part of acc */ 00267 acc_h = (acc >> 32) & 0xffffffff; 00268 00269 /* Apply shift for lower part of acc and upper part of acc */ 00270 acc_h = (uint32_t) acc_l >> lShift | acc_h << uShift; 00271 00272 /* Store the output in the destination buffer in 1.31 format. */ 00273 *pOut = acc_h; 00274 00275 /* Read the second input into Xn2, to reuse the value */ 00276 Xn2 = *pIn++; 00277 00278 /* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ 00279 00280 /* acc += b1 * x[n-1] */ 00281 acc = (q63_t) Xn *b1; 00282 00283 /* acc = b0 * x[n] */ 00284 acc += (q63_t) Xn2 *b0; 00285 00286 /* acc += b[2] * x[n-2] */ 00287 acc += (q63_t) Xn1 *b2; 00288 00289 /* acc += a1 * y[n-1] */ 00290 acc += mult32x64(Yn2, a1); 00291 00292 /* acc += a2 * y[n-2] */ 00293 acc += mult32x64(Yn1, a2); 00294 00295 /* The result is converted to 1.63, Yn1 variable is reused */ 00296 Yn1 = acc << shift; 00297 00298 /* Calc lower part of acc */ 00299 acc_l = acc & 0xffffffff; 00300 00301 /* Calc upper part of acc */ 00302 acc_h = (acc >> 32) & 0xffffffff; 00303 00304 /* Apply shift for lower part of acc and upper part of acc */ 00305 acc_h = (uint32_t) acc_l >> lShift | acc_h << uShift; 00306 00307 /* Read the third input into Xn1, to reuse the value */ 00308 Xn1 = *pIn++; 00309 00310 /* The result is converted to 1.31 */ 00311 /* Store the output in the destination buffer. */ 00312 *(pOut + 1u) = acc_h; 00313 00314 /* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ 00315 00316 /* acc = b0 * x[n] */ 00317 acc = (q63_t) Xn1 *b0; 00318 00319 /* acc += b1 * x[n-1] */ 00320 acc += (q63_t) Xn2 *b1; 00321 00322 /* acc += b[2] * x[n-2] */ 00323 acc += (q63_t) Xn *b2; 00324 00325 /* acc += a1 * y[n-1] */ 00326 acc += mult32x64(Yn1, a1); 00327 00328 /* acc += a2 * y[n-2] */ 00329 acc += mult32x64(Yn2, a2); 00330 00331 /* The result is converted to 1.63, Yn2 variable is reused */ 00332 Yn2 = acc << shift; 00333 00334 /* Calc lower part of acc */ 00335 acc_l = acc & 0xffffffff; 00336 00337 /* Calc upper part of acc */ 00338 acc_h = (acc >> 32) & 0xffffffff; 00339 00340 /* Apply shift for lower part of acc and upper part of acc */ 00341 acc_h = (uint32_t) acc_l >> lShift | acc_h << uShift; 00342 00343 /* Store the output in the destination buffer in 1.31 format. */ 00344 *(pOut + 2u) = acc_h; 00345 00346 /* Read the fourth input into Xn, to reuse the value */ 00347 Xn = *pIn++; 00348 00349 /* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ 00350 /* acc = b0 * x[n] */ 00351 acc = (q63_t) Xn *b0; 00352 00353 /* acc += b1 * x[n-1] */ 00354 acc += (q63_t) Xn1 *b1; 00355 00356 /* acc += b[2] * x[n-2] */ 00357 acc += (q63_t) Xn2 *b2; 00358 00359 /* acc += a1 * y[n-1] */ 00360 acc += mult32x64(Yn2, a1); 00361 00362 /* acc += a2 * y[n-2] */ 00363 acc += mult32x64(Yn1, a2); 00364 00365 /* The result is converted to 1.63, Yn1 variable is reused */ 00366 Yn1 = acc << shift; 00367 00368 /* Calc lower part of acc */ 00369 acc_l = acc & 0xffffffff; 00370 00371 /* Calc upper part of acc */ 00372 acc_h = (acc >> 32) & 0xffffffff; 00373 00374 /* Apply shift for lower part of acc and upper part of acc */ 00375 acc_h = (uint32_t) acc_l >> lShift | acc_h << uShift; 00376 00377 /* Store the output in the destination buffer in 1.31 format. */ 00378 *(pOut + 3u) = acc_h; 00379 00380 /* Every time after the output is computed state should be updated. */ 00381 /* The states should be updated as: */ 00382 /* Xn2 = Xn1 */ 00383 /* Xn1 = Xn */ 00384 /* Yn2 = Yn1 */ 00385 /* Yn1 = acc */ 00386 Xn2 = Xn1; 00387 Xn1 = Xn; 00388 00389 /* update output pointer */ 00390 pOut += 4u; 00391 00392 /* decrement the loop counter */ 00393 sample--; 00394 } 00395 00396 /* If the blockSize is not a multiple of 4, compute any remaining output samples here. 00397 ** No loop unrolling is used. */ 00398 sample = (blockSize & 0x3u); 00399 00400 while(sample > 0u) 00401 { 00402 /* Read the input */ 00403 Xn = *pIn++; 00404 00405 /* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ 00406 00407 /* acc = b0 * x[n] */ 00408 acc = (q63_t) Xn *b0; 00409 /* acc += b1 * x[n-1] */ 00410 acc += (q63_t) Xn1 *b1; 00411 /* acc += b[2] * x[n-2] */ 00412 acc += (q63_t) Xn2 *b2; 00413 /* acc += a1 * y[n-1] */ 00414 acc += mult32x64(Yn1, a1); 00415 /* acc += a2 * y[n-2] */ 00416 acc += mult32x64(Yn2, a2); 00417 00418 /* Every time after the output is computed state should be updated. */ 00419 /* The states should be updated as: */ 00420 /* Xn2 = Xn1 */ 00421 /* Xn1 = Xn */ 00422 /* Yn2 = Yn1 */ 00423 /* Yn1 = acc */ 00424 Xn2 = Xn1; 00425 Xn1 = Xn; 00426 Yn2 = Yn1; 00427 /* The result is converted to 1.63, Yn1 variable is reused */ 00428 Yn1 = acc << shift; 00429 00430 /* Calc lower part of acc */ 00431 acc_l = acc & 0xffffffff; 00432 00433 /* Calc upper part of acc */ 00434 acc_h = (acc >> 32) & 0xffffffff; 00435 00436 /* Apply shift for lower part of acc and upper part of acc */ 00437 acc_h = (uint32_t) acc_l >> lShift | acc_h << uShift; 00438 00439 /* Store the output in the destination buffer in 1.31 format. */ 00440 *pOut++ = acc_h; 00441 //Yn1 = acc << shift; 00442 00443 /* Store the output in the destination buffer in 1.31 format. */ 00444 // *pOut++ = (q31_t) (acc >> (32 - shift)); 00445 00446 /* decrement the loop counter */ 00447 sample--; 00448 } 00449 00450 /* The first stage output is given as input to the second stage. */ 00451 pIn = pDst; 00452 00453 /* Reset to destination buffer working pointer */ 00454 pOut = pDst; 00455 00456 /* Store the updated state variables back into the pState array */ 00457 /* Store the updated state variables back into the pState array */ 00458 *pState++ = (q63_t) Xn1; 00459 *pState++ = (q63_t) Xn2; 00460 *pState++ = Yn1; 00461 *pState++ = Yn2; 00462 00463 } while(--stage); 00464 00465 #else 00466 00467 /* Run the below code for Cortex-M0 */ 00468 00469 do 00470 { 00471 /* Reading the coefficients */ 00472 b0 = *pCoeffs++; 00473 b1 = *pCoeffs++; 00474 b2 = *pCoeffs++; 00475 a1 = *pCoeffs++; 00476 a2 = *pCoeffs++; 00477 00478 /* Reading the state values */ 00479 Xn1 = pState[0]; 00480 Xn2 = pState[1]; 00481 Yn1 = pState[2]; 00482 Yn2 = pState[3]; 00483 00484 /* The variable acc hold output value that is being computed and 00485 * stored in the destination buffer 00486 * acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] 00487 */ 00488 00489 sample = blockSize; 00490 00491 while(sample > 0u) 00492 { 00493 /* Read the input */ 00494 Xn = *pIn++; 00495 00496 /* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ 00497 /* acc = b0 * x[n] */ 00498 acc = (q63_t) Xn *b0; 00499 /* acc += b1 * x[n-1] */ 00500 acc += (q63_t) Xn1 *b1; 00501 /* acc += b[2] * x[n-2] */ 00502 acc += (q63_t) Xn2 *b2; 00503 /* acc += a1 * y[n-1] */ 00504 acc += mult32x64(Yn1, a1); 00505 /* acc += a2 * y[n-2] */ 00506 acc += mult32x64(Yn2, a2); 00507 00508 /* Every time after the output is computed state should be updated. */ 00509 /* The states should be updated as: */ 00510 /* Xn2 = Xn1 */ 00511 /* Xn1 = Xn */ 00512 /* Yn2 = Yn1 */ 00513 /* Yn1 = acc */ 00514 Xn2 = Xn1; 00515 Xn1 = Xn; 00516 Yn2 = Yn1; 00517 00518 /* The result is converted to 1.63, Yn1 variable is reused */ 00519 Yn1 = acc << shift; 00520 00521 /* Calc lower part of acc */ 00522 acc_l = acc & 0xffffffff; 00523 00524 /* Calc upper part of acc */ 00525 acc_h = (acc >> 32) & 0xffffffff; 00526 00527 /* Apply shift for lower part of acc and upper part of acc */ 00528 acc_h = (uint32_t) acc_l >> lShift | acc_h << uShift; 00529 00530 /* Store the output in the destination buffer in 1.31 format. */ 00531 *pOut++ = acc_h; 00532 00533 //Yn1 = acc << shift; 00534 00535 /* Store the output in the destination buffer in 1.31 format. */ 00536 //*pOut++ = (q31_t) (acc >> (32 - shift)); 00537 00538 /* decrement the loop counter */ 00539 sample--; 00540 } 00541 00542 /* The first stage output is given as input to the second stage. */ 00543 pIn = pDst; 00544 00545 /* Reset to destination buffer working pointer */ 00546 pOut = pDst; 00547 00548 /* Store the updated state variables back into the pState array */ 00549 *pState++ = (q63_t) Xn1; 00550 *pState++ = (q63_t) Xn2; 00551 *pState++ = Yn1; 00552 *pState++ = Yn2; 00553 00554 } while(--stage); 00555 00556 #endif /* #ifndef ARM_MATH_CM0_FAMILY */ 00557 } 00558 00559 /** 00560 * @} end of BiquadCascadeDF1_32x64 group 00561 */
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