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resample: use fixed point for resample phase and input rate

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If phase is float, calculations in impl_native_in_len/out_len can
produce wrong results due to rounding error.

It's probably better to not be in the business of predicting
floating-point rounding, so replace this by fixed-point arithmetic.

Also make sure `offset+1` cannot overflow data->filter array in
do_resample_inter* due to float multiplication possibly rounding up.
This commit is contained in:
Pauli Virtanen 2025-07-26 17:23:44 +03:00 • committed by Wim Taymans
parent 3cade43cf3
commit 244d5a1cc1
3 changed files with 61 additions and 32 deletions
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40
spa/plugins/audioconvert/resample-native.c
View file

@ -159,17 +159,31 @@ static void impl_native_update_rate(struct resample *r, double rate)
data->func = data->info->process_full;
}
data->in_rate = in_rate;
if (data->out_rate != out_rate) {
data->phase = data->phase * out_rate / (float)data->out_rate;
data->out_rate = out_rate;
/* Cast to double to avoid overflows */
data->phase.value = (uint64_t)(data->phase.value * (double)out_rate / data->out_rate);
if (data->phase.value >= UINT32_TO_FIXP(out_rate).value)
data->phase.value = UINT32_TO_FIXP(out_rate).value - 1;
}
data->inc = data->in_rate / data->out_rate;
data->frac = data->in_rate % data->out_rate;
spa_log_trace_fp(r->log, "native %p: rate:%f in:%d out:%d phase:%f inc:%d frac:%d", r,
rate, r->i_rate, r->o_rate, data->phase, data->inc, data->frac);
data->in_rate = in_rate;
data->out_rate = out_rate;
data->inc = in_rate / out_rate;
data->frac = UINT32_TO_FIXP(in_rate % out_rate);
spa_log_trace_fp(r->log, "native %p: rate:%f in:%d out:%d phase:%f inc:%d frac:%f", r,
rate, r->i_rate, r->o_rate, FIXP_TO_FLOAT(data->phase),
data->inc, FIXP_TO_FLOAT(data->frac));
}
static uint64_t fixp_floor_a_plus_bc(struct fixp a, uint32_t b, struct fixp c)
{
/* (a + b*c) >> FIXP_SHIFT, with bigger overflow threshold */
uint64_t hi, lo;
hi = (a.value >> FIXP_SHIFT) + b * (c.value >> FIXP_SHIFT);
lo = (a.value & FIXP_MASK) + b * (c.value & FIXP_MASK);
return hi + (lo >> FIXP_SHIFT);
}
static uint32_t impl_native_in_len(struct resample *r, uint32_t out_len)
@ -177,7 +191,7 @@ static uint32_t impl_native_in_len(struct resample *r, uint32_t out_len)
struct native_data *data = r->data;
uint32_t in_len;
in_len = (uint32_t)((data->phase + out_len * data->frac) / data->out_rate);
in_len = fixp_floor_a_plus_bc(data->phase, out_len, data->frac) / data->out_rate;
in_len += out_len * data->inc + (data->n_taps - data->hist);
spa_log_trace_fp(r->log, "native %p: hist:%d %d->%d", r, data->hist, out_len, in_len);
@ -191,7 +205,7 @@ static uint32_t impl_native_out_len(struct resample *r, uint32_t in_len)
uint32_t out_len;
in_len = in_len - SPA_MIN(in_len, data->n_taps - data->hist);
out_len = (uint32_t)(in_len * data->out_rate - data->phase);
out_len = in_len * data->out_rate - FIXP_TO_UINT32(data->phase);
out_len = (out_len + data->in_rate - 1) / data->in_rate;
spa_log_trace_fp(r->log, "native %p: hist:%d %d->%d", r, data->hist, in_len, out_len);
@ -300,7 +314,7 @@ static void impl_native_reset (struct resample *r)
d->hist = d->n_taps - 1;
else
d->hist = d->n_taps / 2;
d->phase = 0;
d->phase.value = 0;
}
static uint32_t impl_native_delay (struct resample *r)
@ -315,13 +329,13 @@ static float impl_native_phase (struct resample *r)
float pho = 0;
if (d->func == d->info->process_full) {
pho = -(float)((int32_t)d->phase) / d->out_rate;
pho = -(float)FIXP_TO_UINT32(d->phase) / d->out_rate;
/* XXX: this is how it seems to behave, but not clear why */
if (d->hist >= d->n_taps - 1)
pho += 1.0f;
} else if (d->func == d->info->process_inter) {
pho = -d->phase / d->out_rate;
pho = -FIXP_TO_FLOAT(d->phase) / d->out_rate;
/* XXX: this is how it seems to behave, but not clear why */
if (d->hist >= d->n_taps - 1)
@ -388,7 +402,7 @@ int resample_native_init(struct resample *r)
d->in_rate = in_rate;
d->out_rate = out_rate;
d->gcd = gcd;
d->pm = (float)n_phases / r->o_rate;
d->pm = (float)n_phases / r->o_rate / FIXP_SCALE;
d->filter = SPA_PTROFF_ALIGN(d, sizeof(struct native_data), 64, float);
d->hist_mem = SPA_PTROFF_ALIGN(d->filter, filter_size, 64, float);
d->history = SPA_PTROFF(d->hist_mem, history_size, float*);