File hbdecim_core.h¶

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Halfband 2:1 decimator for CF32 IQ samples. More...

• #include "clib_common.h"
• #include "dp_state.h"

Classes¶

Public Functions¶

Macros¶

Detailed Description¶

Lifted from dp_hbdecim_cf32_t (c/src/hbdecim.c). Only the cf32 variant is ported; dp_hbdecim_r2cf32 (real-input D2) is a separate object and a separate session.

Algorithm: two dual-write circular delay lines hold even-indexed and odd-indexed input samples separately. Per output sample: * Push x(2m) → even delay line. * Push x(2m+1) → odd delay line. * Compute symmetric FIR (N/2 paired multiplies) + scaled delay tap.

Which delay line carries the FIR is determined by N: N even (fir_on_even=1): FIR on even_dl; delay from odd_dl(centre). N odd (fir_on_even=0): FIR on odd_dl at offset +1; delay from even_dl(centre).

Coefficients are scaled by 0.5 inside hbdecim_create — this is the polyphase identity normalisation; do not remove it.

Lifecycle:

hbdecim_state_t *r = hbdecim_create(num_taps, h_fir);
size_t n = hbdecim_execute(r, in, num_in, out, max_out);
hbdecim_destroy(r);

Public Functions Documentation¶

function hbdecim_create¶

Allocate and initialise a halfband 2:1 decimator.

hbdecim_state_t * hbdecim_create (
    size_t num_taps,
    const float * h
) 

Parameters:

• num_taps Length of the FIR branch (the row from kaiser_prototype(phases=2) that has more than one significant coefficient).
• h FIR coefficients, length num_taps (float32). Copied internally and scaled by 0.5.

Returns:

Non-NULL on success, NULL on invalid args or OOM.

function hbdecim_destroy¶

void hbdecim_destroy (
    hbdecim_state_t * r
) 

Free all resources. NULL is a no-op.

function hbdecim_execute¶

Decimate a block of CF32 samples by 2.

size_t hbdecim_execute (
    hbdecim_state_t * r,
    const float _Complex * in,
    size_t num_in,
    float _Complex * out,
    size_t max_out
) 

Processes input pairs (even, odd); one output per pair. If num_in is odd, the trailing even sample is buffered and consumed on the next call.

Output-buffer sizing: allocate at least (num_in + 1) / 2 samples.

Parameters:

• r Must be non-NULL.
• in Input CF32 samples.
• num_in Number of input samples.
• out Output buffer.
• max_out Capacity of out in samples.

Returns:

Number of output samples written.

function hbdecim_get_num_taps¶

size_t hbdecim_get_num_taps (
    const hbdecim_state_t * r
) 

Returns the FIR branch length passed to hbdecim_create.

function hbdecim_get_rate¶

double hbdecim_get_rate (
    const hbdecim_state_t * r
) 

Always returns 0.5 (rate is fixed by design).

function hbdecim_get_state¶

Serialize r's mutable state intoblob .

void hbdecim_get_state (
    const hbdecim_state_t * r,
    void * blob
) 

function hbdecim_reset¶

void hbdecim_reset (
    hbdecim_state_t * r
) 

Zero both delay lines and clear the pending-sample flag. num_taps and coefficients are preserved.

function hbdecim_set_state¶

Restore mutable state from blob (same num_taps).

int hbdecim_set_state (
    hbdecim_state_t * r,
    const void * blob
) 

Returns:

DP_OK, or DP_ERR_INVALID if the blob's envelope rejects.

function hbdecim_state_bytes¶

Bytes hbdecim_get_state() writes forr (envelope + payload).

size_t hbdecim_state_bytes (
    const hbdecim_state_t * r
) 

Macro Definition Documentation¶

define HBDECIM_STATE_MAGIC¶

#define HBDECIM_STATE_MAGIC `DP_FOURCC ('H', 'B', 'D', 'C')`

define HBDECIM_STATE_VERSION¶

#define HBDECIM_STATE_VERSION `1u`

The documentation for this class was generated from the following file native/inc/hbdecim/hbdecim_core.h