| /* ---------------------------------------------------------------------- |
| * Copyright (C) 2010-2014 ARM Limited. All rights reserved. |
| * |
| * $Date: 19. March 2015 |
| * $Revision: V.1.4.5 |
| * |
| * Project: CMSIS DSP Library |
| * Title: arm_std_q15.c |
| * |
| * Description: Standard deviation of an array of Q15 type. |
| * |
| * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0 |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * - Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * - Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in |
| * the documentation and/or other materials provided with the |
| * distribution. |
| * - Neither the name of ARM LIMITED nor the names of its contributors |
| * may be used to endorse or promote products derived from this |
| * software without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS |
| * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE |
| * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, |
| * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, |
| * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; |
| * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER |
| * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
| * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN |
| * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
| * POSSIBILITY OF SUCH DAMAGE. |
| * -------------------------------------------------------------------- */ |
| |
| #include "arm_math.h" |
| |
| /** |
| * @ingroup groupStats |
| */ |
| |
| /** |
| * @addtogroup STD |
| * @{ |
| */ |
| |
| /** |
| * @brief Standard deviation of the elements of a Q15 vector. |
| * @param[in] *pSrc points to the input vector |
| * @param[in] blockSize length of the input vector |
| * @param[out] *pResult standard deviation value returned here |
| * @return none. |
| * |
| * @details |
| * <b>Scaling and Overflow Behavior:</b> |
| * |
| * \par |
| * The function is implemented using a 64-bit internal accumulator. |
| * The input is represented in 1.15 format. |
| * Intermediate multiplication yields a 2.30 format, and this |
| * result is added without saturation to a 64-bit accumulator in 34.30 format. |
| * With 33 guard bits in the accumulator, there is no risk of overflow, and the |
| * full precision of the intermediate multiplication is preserved. |
| * Finally, the 34.30 result is truncated to 34.15 format by discarding the lower |
| * 15 bits, and then saturated to yield a result in 1.15 format. |
| */ |
| |
| void arm_std_q15( |
| q15_t * pSrc, |
| uint32_t blockSize, |
| q15_t * pResult) |
| { |
| q31_t sum = 0; /* Accumulator */ |
| q31_t meanOfSquares, squareOfMean; /* square of mean and mean of square */ |
| uint32_t blkCnt; /* loop counter */ |
| q63_t sumOfSquares = 0; /* Accumulator */ |
| |
| #ifndef ARM_MATH_CM0_FAMILY |
| |
| /* Run the below code for Cortex-M4 and Cortex-M3 */ |
| |
| q31_t in; /* input value */ |
| q15_t in1; /* input value */ |
| |
| if(blockSize == 1) |
| { |
| *pResult = 0; |
| return; |
| } |
| |
| /*loop Unrolling */ |
| blkCnt = blockSize >> 2u; |
| |
| /* First part of the processing with loop unrolling. Compute 4 outputs at a time. |
| ** a second loop below computes the remaining 1 to 3 samples. */ |
| while(blkCnt > 0u) |
| { |
| /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */ |
| /* Compute Sum of squares of the input samples |
| * and then store the result in a temporary variable, sum. */ |
| in = *__SIMD32(pSrc)++; |
| sum += ((in << 16) >> 16); |
| sum += (in >> 16); |
| sumOfSquares = __SMLALD(in, in, sumOfSquares); |
| in = *__SIMD32(pSrc)++; |
| sum += ((in << 16) >> 16); |
| sum += (in >> 16); |
| sumOfSquares = __SMLALD(in, in, sumOfSquares); |
| |
| /* 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. */ |
| blkCnt = blockSize % 0x4u; |
| |
| while(blkCnt > 0u) |
| { |
| /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */ |
| /* Compute Sum of squares of the input samples |
| * and then store the result in a temporary variable, sum. */ |
| in1 = *pSrc++; |
| sumOfSquares = __SMLALD(in1, in1, sumOfSquares); |
| sum += in1; |
| |
| /* Decrement the loop counter */ |
| blkCnt--; |
| } |
| |
| /* Compute Mean of squares of the input samples |
| * and then store the result in a temporary variable, meanOfSquares. */ |
| meanOfSquares = (q31_t)(sumOfSquares / (q63_t)(blockSize - 1)); |
| |
| /* Compute square of mean */ |
| squareOfMean = (q31_t) ((q63_t)sum * sum / (q63_t)(blockSize * (blockSize - 1))); |
| |
| /* mean of the squares minus the square of the mean. */ |
| /* Compute standard deviation and store the result to the destination */ |
| arm_sqrt_q15(__SSAT((meanOfSquares - squareOfMean) >> 15, 16u), pResult); |
| |
| #else |
| |
| /* Run the below code for Cortex-M0 */ |
| q15_t in; /* input value */ |
| |
| if(blockSize == 1) |
| { |
| *pResult = 0; |
| return; |
| } |
| |
| /* Loop over blockSize number of values */ |
| blkCnt = blockSize; |
| |
| while(blkCnt > 0u) |
| { |
| /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */ |
| /* Compute Sum of squares of the input samples |
| * and then store the result in a temporary variable, sumOfSquares. */ |
| in = *pSrc++; |
| sumOfSquares += (in * in); |
| |
| /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */ |
| /* Compute sum of all input values and then store the result in a temporary variable, sum. */ |
| sum += in; |
| |
| /* Decrement the loop counter */ |
| blkCnt--; |
| } |
| |
| /* Compute Mean of squares of the input samples |
| * and then store the result in a temporary variable, meanOfSquares. */ |
| meanOfSquares = (q31_t)(sumOfSquares / (q63_t)(blockSize - 1)); |
| |
| /* Compute square of mean */ |
| squareOfMean = (q31_t) ((q63_t)sum * sum / (q63_t)(blockSize * (blockSize - 1))); |
| |
| /* mean of the squares minus the square of the mean. */ |
| /* Compute standard deviation and store the result to the destination */ |
| arm_sqrt_q15(__SSAT((meanOfSquares - squareOfMean) >> 15, 16u), pResult); |
| |
| #endif /* #ifndef ARM_MATH_CM0_FAMILY */ |
| |
| |
| } |
| |
| /** |
| * @} end of STD group |
| */ |