lpf.h

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#ifndef LIBA_LPF_H
#define LIBA_LPF_H
 
#include "math.h"
 
typedef struct a_lpf
{
    a_float alpha; 
    a_float output; 
#if defined(__cplusplus)
    A_INLINE void gen(a_float fc, a_float ts)
    {
        alpha = ts / (A_FLOAT_1_TAU / fc + ts);
    }
    A_INLINE a_float operator()(a_float x)
    {
        output *= 1 - alpha;
        output += x * alpha;
        return output;
    }
    A_INLINE void zero() { output = 0; }
#endif /* __cplusplus */
} a_lpf;
#if defined(__cplusplus)
namespace a
{
typedef struct a_lpf lpf;
} /* namespace a */
#endif /* __cplusplus */
// clang-format off
#if defined(__cplusplus)
#define A_LPF_INIT(alpha) {a_float_c(alpha), 0}
#define A_LPF_INIT2(fc, ts) {A_LPF_GEN(fc, ts), 0}
#else /* !__cplusplus */
#define A_LPF_INIT(alpha) (a_lpf){a_float_c(alpha), 0}
#define A_LPF_INIT2(fc, ts) (a_lpf){A_LPF_GEN(fc, ts), 0}
#endif /* __cplusplus */
// clang-format on
#define A_LPF_GEN(fc, ts) (a_float_c(ts) / (A_FLOAT_1_TAU / a_float_c(fc) + a_float_c(ts)))
 
A_INTERN a_float a_lpf_gen(a_float fc, a_float ts)
{
    return ts / (A_FLOAT_1_TAU / fc + ts);
}
 
A_INTERN void a_lpf_init(a_lpf *ctx, a_float alpha)
{
    ctx->alpha = alpha;
    ctx->output = 0;
}
 
A_INTERN a_float a_lpf_iter(a_lpf *ctx, a_float x)
{
    ctx->output *= 1 - ctx->alpha;
    ctx->output += x * ctx->alpha;
    return ctx->output;
}
 
A_INTERN void a_lpf_zero(a_lpf *ctx) { ctx->output = 0; }
 
#endif /* a/lpf.h */