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Synthio has fixed point overflow errors #10286

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gamblor21 opened this issue Apr 23, 2025 · 1 comment
Open

Synthio has fixed point overflow errors #10286

gamblor21 opened this issue Apr 23, 2025 · 1 comment
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@gamblor21
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audio bug rp2 Both RP2 microcontrollers
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Long term

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@gamblor21
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Synthio has one (and likely more) spots where it is possible to overflow the int32_t used as an intermediary while doing fixed point math.

This function multiplies an int32_t by int16_t which can exceed the 32 bit size.

circuitpython/shared-module/synthio/__init__.c

Line 272 in ceda2f0

static void sum_with_loudness(int32_t *out_buffer32, int32_t *tmp_buffer32, int16_t loudness[2], size_t dur, int synth_chan) {

There are likely other cases as well.

The probable fix is to add a function to ensure the values are saturated after every calculation.
audiofreeverb does this

circuitpython/shared-module/audiofreeverb/Freeverb.c

Line 221 in bcf37e0

static int16_t sat16(int32_t n, int rshift) {

This issue is most likely the cause for #10200.
@gamblor21 gamblor21 added audio bug rp2 Both RP2 microcontrollers labels Apr 23, 2025
@gamblor21 gamblor21 self-assigned this Apr 23, 2025
@gamblor21 gamblor21 added this to the Long term milestone Apr 23, 2025
@gamblor21 gamblor21 mentioned this issue Apr 23, 2025
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#10288 should have caught most of the cases. Will keep this issue open short term to see if others show up (unless others think we should close it, in case feel free).

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