| /* ---------------------------------------------------------------------- |
| * Copyright (C) 2010 ARM Limited. All rights reserved. |
| * |
| * $Date: 15. July 2011 |
| * $Revision: V1.0.10 |
| * |
| * 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 |
| * |
| * 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 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) |
| { |
| q63_t sum = 0; /* Accumulator */ |
| q31_t meanOfSquares, squareOfMean; /* square of mean and mean of square */ |
| q15_t mean; /* mean */ |
| uint32_t blkCnt; /* loop counter */ |
| q15_t t; /* Temporary variable */ |
| |
| #ifndef ARM_MATH_CM0 |
| |
| /* Run the below code for Cortex-M4 and Cortex-M3 */ |
| |
| q15_t *pIn; /* Temporary pointer */ |
| q31_t in; /* input value */ |
| q15_t in1; /* input value */ |
| |
| pIn = pSrc; |
| |
| /*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 = __SMLALD(in, in, sum); |
| in = *__SIMD32(pSrc)++; |
| sum = __SMLALD(in, in, sum); |
| |
| /* 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++; |
| sum = __SMLALD(in1, in1, sum); |
| |
| /* Decrement the loop counter */ |
| blkCnt--; |
| } |
| |
| /* Compute Mean of squares of the input samples |
| * and then store the result in a temporary variable, meanOfSquares. */ |
| t = (q15_t) ((1.0 / (blockSize - 1)) * 16384LL); |
| sum = __SSAT((sum >> 15u), 16u); |
| |
| meanOfSquares = (q31_t) ((sum * t) >> 14u); |
| |
| /* Reset the accumulator */ |
| sum = 0; |
| |
| /*loop Unrolling */ |
| blkCnt = blockSize >> 2u; |
| |
| /* Reset the input working pointer */ |
| pSrc = pIn; |
| |
| /* 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[1] + A[2] + ... + A[blockSize-1]) */ |
| /* Compute sum of all input values and then store the result in a temporary variable, sum. */ |
| sum += *pSrc++; |
| sum += *pSrc++; |
| sum += *pSrc++; |
| sum += *pSrc++; |
| |
| /* 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[1] + A[2] + ... + A[blockSize-1]) */ |
| /* Compute sum of all input values and then store the result in a temporary variable, sum. */ |
| sum += *pSrc++; |
| |
| /* Decrement the loop counter */ |
| blkCnt--; |
| } |
| /* Compute mean of all input values */ |
| t = (q15_t) ((1.0 / (blockSize * (blockSize - 1))) * 32768LL); |
| mean = (q15_t) __SSAT(sum, 16u); |
| |
| /* Compute square of mean */ |
| squareOfMean = ((q31_t) mean * mean) >> 15; |
| squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 15); |
| |
| /* mean of the squares minus the square of the mean. */ |
| in1 = (q15_t) (meanOfSquares - squareOfMean); |
| |
| /* Compute standard deviation and store the result to the destination */ |
| arm_sqrt_q15(in1, pResult); |
| |
| #else |
| |
| /* Run the below code for Cortex-M0 */ |
| |
| q63_t sumOfSquares = 0; /* Accumulator */ |
| q15_t in; /* input value */ |
| /* 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. */ |
| t = (q15_t) ((1.0 / (blockSize - 1)) * 16384LL); |
| sumOfSquares = __SSAT((sumOfSquares >> 15u), 16u); |
| meanOfSquares = (q31_t) ((sumOfSquares * t) >> 14u); |
| |
| /* Compute mean of all input values */ |
| mean = (q15_t) __SSAT(sum, 16u); |
| |
| /* Compute square of mean of the input samples |
| * and then store the result in a temporary variable, squareOfMean.*/ |
| t = (q15_t) ((1.0 / (blockSize * (blockSize - 1))) * 32768LL); |
| squareOfMean = ((q31_t) mean * mean) >> 15; |
| squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 15); |
| |
| /* mean of the squares minus the square of the mean. */ |
| in = (q15_t) (meanOfSquares - squareOfMean); |
| |
| /* Compute standard deviation and store the result to the destination */ |
| arm_sqrt_q15(in, pResult); |
| |
| #endif /* #ifndef ARM_MATH_CM0 */ |
| |
| |
| } |
| |
| /** |
| * @} end of STD group |
| */ |
