bl_mcu_sdk/examples/dsp/StatisticsFunctions_part1/std.c

#include "ref.h"

void ref_std_f32(float32_t *pSrc, uint32_t blockSize, float32_t *pResult)
{
    uint32_t i;
    float32_t sum = 0, sumsq = 0;

    if (blockSize == 1) {
        *pResult = 0;
        return;
    }

    for (i = 0; i < blockSize; i++) {
        sum += pSrc[i];
        sumsq += pSrc[i] * pSrc[i];
    }
    *pResult = sqrtf((sumsq - sum * sum / (float32_t)blockSize) /
                     ((float32_t)blockSize - 1));
}

void ref_std_q31(q31_t *pSrc, uint32_t blockSize, q31_t *pResult)
{
    uint32_t i;
    q63_t sum = 0, sumsq = 0;
    q31_t in;

    if (blockSize == 1) {
        *pResult = 0;
        return;
    }

    for (i = 0; i < blockSize; i++) {
        in = pSrc[i] >> 8;
        sum += in;
        sumsq += (q63_t)in * in;
    }
    sumsq /= (q63_t)(blockSize - 1);
    sum = sum * sum / (q63_t)(blockSize * (blockSize - 1));
    *pResult = (q31_t)(sqrtf((float)((sumsq - sum) >> 15) / 2147483648.0f) *
                       2147483648.0f);
}

void ref_std_q15(q15_t *pSrc, uint32_t blockSize, q15_t *pResult)
{
    uint32_t i;
    q31_t sum = 0;
    q63_t sumsq = 0;

    if (blockSize == 1) {
        *pResult = 0;
        return;
    }

    for (i = 0; i < blockSize; i++) {
        sum += pSrc[i];
        sumsq += (q63_t)pSrc[i] * pSrc[i];
    }
    sumsq /= (q63_t)(blockSize - 1);
    sum = (q31_t)((q63_t)sum * sum / (q63_t)(blockSize * (blockSize - 1)));
    *pResult = (q15_t)(
        sqrtf((float)ref_sat_q15((sumsq - sum) >> 15) / 32768.0f) * 32768.0f);
}