ema v0.1.0

First-order lag filter with a power-of-two smoothing factor.

Application scenarios

• Battery voltage or temperature needs a slow, memory-light smooth.
• A control loop needs a first-order response with a known time constant.
• A display value should follow a trend without jumping.

Contract

void ema_filter_init(ema_filter_t *filter, int32_t initial, uint8_t shift);
int32_t ema_filter_step(ema_filter_t *filter, int32_t sample);
void ema_filter_reset(ema_filter_t *filter, int32_t value);

• shift is 0..15; the smoothing factor is 2^shift.
• shift = 0 follows the sample exactly.
• Division truncates toward zero, so negative inputs round toward zero.
• O(1); no allocation.

Parameters

• Time constant is about 2^shift samples.
• Larger shift: smoother, more lag; smaller shift: faster, more noise.

Memory and timing

• 8 bytes of state; one shift and one division per sample.

Integration

ema_filter_t filter;
ema_filter_init(&filter, 0, 3);   // factor 8
int32_t smooth = ema_filter_step(&filter, adc_read());

When not to use

• Impulses must be removed; a spike still moves the output.
• Exact linear-phase filtering is required; use a symmetric FIR.

Verification

make test covers shift 0, positive and negative steps, reset, and shift clamping.

Behavior reference: Padauk Soft_Filter/AD_filter_07.

int32_t value;
uint8_t shift;