moving-average v0.1.0

Average the last N samples with a fixed-size ring buffer.

Application scenarios

• Battery voltage or temperature changes slowly, and the display must not flicker.
• An ADC channel has white noise but no large impulses.
• A control loop needs a simple, bounded-lag smooth.

Contract

void moving_average_init(moving_average_t *filter, uint16_t *window, uint8_t size);
uint16_t moving_average_step(moving_average_t *filter, uint16_t sample);
void moving_average_reset(moving_average_t *filter);

• The caller supplies window, an array of size elements.
• size must be 1..255.
• A uint32_t sum holds up to 255 uint16_t samples without overflow.
• Output is rounded to the nearest integer.
• O(1) per sample.

Parameters

• Larger size: smoother but slower; the step response reaches about 63% after N samples.
• A spike still moves the mean by spike/N; use median first if spikes exist.

Memory and timing

• State is 12 bytes plus the caller's 2*size bytes.
• O(1) per sample; no division until the output is computed.

Integration

uint16_t window[8];
moving_average_t filter;
moving_average_init(&filter, window, 8);
uint16_t smooth = moving_average_step(&filter, adc_read());

When not to use

• Impulses matter; one spike contaminates the window.
• Very fast response is required; use ema with a small shift.

Verification

make test covers warm-up, wrap, rounding, size 1, size 0, and reset.

Behavior reference: Padauk Soft_Filter/AD_filter_04.

uint16_t *window;
uint8_t size;
uint8_t count;
uint8_t index;
uint32_t sum;