已知三轴加速度数据，利用低通滤波，华东窗口以及波峰波谷的检测实现对步数的计步，C语言来写

以下是一个基于三轴加速度数据的计步算法示例，使用了低通滤波、华东窗口和波峰波谷检测。请注意，这是一个简单的示例，实际应用中可能需要根据具体情况进行调整和优化。

#include <stdio.h>
#include <math.h>

#define SAMPLE_RATE 50 // 采样率，单位 Hz
#define WINDOW_SIZE 20 // 窗口大小，单位采样点
#define THRESHOLD_FACTOR 0.25 // 波峰波谷阈值系数
#define MIN_STEP_INTERVAL 300 // 最小步间隔，单位毫秒

// 低通滤波器
typedef struct {
    double a1, a2, b0, b1, b2;
    double x1, x2, y1, y2;
} LowPassFilter;

void initLowPassFilter(LowPassFilter* filter, double cutoffFreq) {
    double omega = 2.0 * M_PI * cutoffFreq / SAMPLE_RATE;
    double alpha = sin(omega) / (2.0 * 0.707);
    double beta = sqrt(2.0) * alpha;
    double a0 = 1.0 + beta + alpha * alpha;
    filter->a1 = (2.0 * (alpha * alpha - 1.0)) / a0;
    filter->a2 = (1.0 - beta + alpha * alpha) / a0;
    filter->b0 = (alpha * alpha) / a0;
    filter->b1 = (2.0 * alpha * alpha) / a0;
    filter->b2 = (alpha * alpha) / a0;
    filter->x1 = 0.0;
    filter->x2 = 0.0;
    filter->y1 = 0.0;
    filter->y2 = 0.0;
}

double lowPassFilter(LowPassFilter* filter, double x) {
    double y = filter->b0 * x + filter->b1 * filter->x1 + filter->b2 * filter->x2
             - filter->a1 * filter->y1 - filter->a2 * filter->y2;
    filter->x2 = filter->x1;
    filter->x1 = x;
    filter->y2 = filter->y1;
    filter->y1 = y;
    return y;
}

// 华东窗口
typedef struct {
    double* buffer;
    int size;
    int head;
    double sum;
} MovingWindow;

void initMovingWindow(MovingWindow* window, int size) {
    window->buffer = (double*) malloc(size * sizeof(double));
    window->size = size;
    window->head = 0;
    window->sum = 0.0;
}

void destroyMovingWindow(MovingWindow* window) {
    free(window->buffer);
}

void addToMovingWindow(MovingWindow* window, double x) {
    window->sum += x;
    window->sum -= window->buffer[window->head];
    window->buffer[window->head] = x;
    window->head = (window->head + 1) % window->size;
}

double getMovingWindowAvg(MovingWindow* window) {
    return window->sum / window->size;
}

// 波峰波谷检测状态
typedef enum {
    STATE_IDLE,
    STATE_RISING,
    STATE_FALLING
} PeakDetectionState;

// 波峰波谷检测
typedef struct {
    PeakDetectionState state;
    double threshold;
    double lastValue;
    double lastPeak;
    double lastValley;
} PeakDetector;

void initPeakDetector(PeakDetector* detector, double threshold) {
    detector->state = STATE_IDLE;
    detector->threshold = threshold;
    detector->lastValue = 0.0;
    detector->lastPeak = 0.0;
    detector->lastValley = 0.0;
}

int updatePeakDetector(PeakDetector* detector, double value, double* peak, double* valley) {
    switch (detector->state) {
        case STATE_IDLE:
            if (value > detector->lastValue + detector->threshold) {
                detector->state = STATE_RISING;
                detector->lastPeak = value;
                *peak = value;
                return 1;
            } else if (value < detector->lastValue - detector->threshold) {
                detector->state = STATE_FALLING;
                detector->lastValley = value;
                *valley = value;
                return 1;
            }
            break;
        case STATE_RISING:
            if (value < detector->lastPeak) {
                detector->state = STATE_FALLING;
                detector->lastValley = value;
                *valley = value;
                return 1;
            }
            break;
        case STATE_FALLING:
            if (value > detector->lastValley) {
                detector->state = STATE_RISING;
                detector->lastPeak = value;
                *peak = value;
                return 1;
            }
            break;
    }
    detector->lastValue = value;
    return 0;
}

// 计步器
typedef struct {
    LowPassFilter filter;
    MovingWindow window;
    PeakDetector peakDetector;
    int stepCount;
    int lastStepTime;
} StepCounter;

void initStepCounter(StepCounter* counter) {
    initLowPassFilter(&counter->filter, 5.0);
    initMovingWindow(&counter->window, WINDOW_SIZE);
    initPeakDetector(&counter->peakDetector, THRESHOLD_FACTOR * getMovingWindowAvg(&counter->window));
    counter->stepCount = 0;
    counter->lastStepTime = 0;
}

void destroyStepCounter(StepCounter* counter) {
    destroyMovingWindow(&counter->window);
}

int updateStepCounter(StepCounter* counter, double x, double y, double z) {
    double norm = sqrt(x * x + y * y + z * z);
    double filtered = lowPassFilter(&counter->filter, norm);
    addToMovingWindow(&counter->window, filtered);
    double avg = getMovingWindowAvg(&counter->window);
    double peak = 0.0, valley = 0.0;
    if (updatePeakDetector(&counter->peakDetector, filtered - avg, &peak, &valley)) {
        int interval = SAMPLE_RATE * (peak - valley) / norm;
        if (interval > MIN_STEP_INTERVAL && counter->lastStepTime + interval < SAMPLE_RATE * 2) {
            counter->stepCount++;
            counter->lastStepTime += interval;
            return 1;
        }
    }
    return 0;
}

int main() {
    // 假设有一组加速度数据 ax, ay, az，每秒50个样本
    double ax[1000], ay[1000], az[1000];
    // 初始化计步器
    StepCounter counter;
    initStepCounter(&counter);
    // 处理加速度数据
    for (int i = 0; i < 1000; i++) {
        int step = updateStepCounter(&counter, ax[i], ay[i], az[i]);
        if (step) {
            printf("Step %d detected\n", counter.stepCount);
        }
    }
    // 销毁计步器
    destroyStepCounter(&counter);
    return 0;
}