| /* ---------------------------------------------------------------------- |
| * Copyright (C) 2010 ARM Limited. All rights reserved. |
| * |
| * $Date: 15. July 2011 |
| * $Revision: V1.0.10 |
| * |
| * Project: CMSIS DSP Library |
| * Title: arm_var_q31.c |
| * |
| * Description: Variance of an array of Q31 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 variance |
| * @{ |
| */ |
| |
| /** |
| * @brief Variance of the elements of a Q31 vector. |
| * @param[in] *pSrc points to the input vector |
| * @param[in] blockSize length of the input vector |
| * @param[out] *pResult variance value returned here |
| * @return none. |
| * |
| * @details |
| * <b>Scaling and Overflow Behavior:</b> |
| * |
| *\par |
| * The function is implemented using an internal 64-bit accumulator. |
| * The input is represented in 1.31 format, and intermediate multiplication |
| * yields a 2.62 format. |
| * The accumulator maintains full precision of the intermediate multiplication results, |
| * but provides only a single guard bit. |
| * There is no saturation on intermediate additions. |
| * If the accumulator overflows it wraps around and distorts the result. |
| * In order to avoid overflows completely the input signal must be scaled down by |
| * log2(blockSize) bits, as a total of blockSize additions are performed internally. |
| * Finally, the 2.62 accumulator is right shifted by 31 bits to yield a 1.31 format value. |
| * |
| */ |
| |
| |
| void arm_var_q31( |
| q31_t * pSrc, |
| uint32_t blockSize, |
| q63_t * pResult) |
| { |
| q63_t sum = 0; /* Accumulator */ |
| q31_t meanOfSquares, squareOfMean; /* Mean of square and square of mean */ |
| q31_t mean; /* Mean */ |
| q31_t in; /* Input variable */ |
| q31_t t; /* Temporary variable */ |
| uint32_t blkCnt; /* loop counter */ |
| |
| #ifndef ARM_MATH_CM0 |
| |
| /* Run the below code for Cortex-M4 and Cortex-M3 */ |
| |
| q31_t *pIn; /* Temporary pointer */ |
| |
| 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 = *pSrc++; |
| sum += ((q63_t) (in) * (in)); |
| in = *pSrc++; |
| sum += ((q63_t) (in) * (in)); |
| in = *pSrc++; |
| sum += ((q63_t) (in) * (in)); |
| in = *pSrc++; |
| sum += ((q63_t) (in) * (in)); |
| |
| /* 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. */ |
| in = *pSrc++; |
| sum += ((q63_t) (in) * (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 = (q31_t) ((1.0 / (blockSize - 1)) * 1073741824LL); |
| sum = (sum >> 31); |
| meanOfSquares = (q31_t) ((sum * t) >> 30); |
| |
| /* 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--; |
| } |
| |
| #else |
| |
| /* Run the below code for Cortex-M0 */ |
| |
| q63_t sumOfSquares = 0; /* Accumulator */ |
| /* 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 += ((q63_t) (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 = (q31_t) ((1.0 / (blockSize - 1)) * 1073741824LL); |
| sumOfSquares = (sumOfSquares >> 31); |
| meanOfSquares = (q31_t) ((sumOfSquares * t) >> 30); |
| |
| #endif /* #ifndef ARM_MATH_CM0 */ |
| |
| /* Compute mean of all input values */ |
| t = (q31_t) ((1.0 / (blockSize * (blockSize - 1u))) * 2147483648LL); |
| mean = (q31_t) (sum); |
| |
| /* Compute square of mean */ |
| squareOfMean = (q31_t) (((q63_t) mean * mean) >> 31); |
| squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 31); |
| |
| /* Compute variance and then store the result to the destination */ |
| *pResult = (q63_t) meanOfSquares - squareOfMean; |
| |
| } |
| |
| /** |
| * @} end of variance group |
| */ |