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util/spkmodem-recv: don't use modulus on decode

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it's slow on older compilers/systems that don't optimise.

instead, we branch (cheaper) and just do an above or
equal comparison), resetting appropriately or subtracting.

should yield an actually useful performance gain, on older
systems. a bit theoretical on modern systems, which optimise
well (modern compilers will produce assembly code much like
what the new C code is doing)

Signed-off-by: Leah Rowe <leah@libreboot.org>
This commit is contained in:
Leah Rowe
2026-03-12 04:39:00 +00:00
parent 19e0249a8a
commit 54936a45a5
1 changed files with 9 additions and 6 deletions
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util/spkmodem_recv/spkmodem-recv.c
+9 -6
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@@ -142,7 +142,9 @@ decode_pulse(struct decoder_state *st)
size_t n;
int next;
next = (st->ringpos + SAMPLES_PER_FRAME) % MAX_SAMPLES;
next = st->ringpos + SAMPLES_PER_FRAME;
if (next >= MAX_SAMPLES)
next -= MAX_SAMPLES;
st->freq_data -= st->pulse[st->ringpos];
st->freq_data += st->pulse[next];
@@ -155,14 +157,15 @@ decode_pulse(struct decoder_state *st)
err(errno, "stdin read");
}
if (abs(st->frame[st->ringpos]) > THRESHOLD)
st->pulse[st->ringpos] = 1;
else
st->pulse[st->ringpos] = 0;
st->pulse[st->ringpos] =
abs(st->frame[st->ringpos]) > THRESHOLD;
st->freq_separator += st->pulse[st->ringpos];
st->ringpos = (st->ringpos + 1) % MAX_SAMPLES;
st->ringpos++;
if (st->ringpos >= MAX_SAMPLES)
st->ringpos = 0;
st->sample_count++;
}