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flac: fix off-by-one in sample conversion #38

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Sep 2, 2018
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flac: fix off-by-one in sample conversion #38

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flac: fix off-by-one in sample conversion 
Issue spotted by @mehrvarz.
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@mewmew
mewmew committed Aug 17, 2018
commit 26ee6de59566eb42356e9518c1e11aa3d9eadc5d
26 changes: 14 additions & 12 deletions flac/decode.go
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Original file line number Diff line number Diff line change
Expand Up @@ -85,36 +85,38 @@ func (d *decoder) refill() error {
// Decode audio samples.
bps := d.stream.Info.BitsPerSample
nchannels := d.stream.Info.NChannels
s := 1 << (bps - 1)
q := 1 / float64(s)
switch {
case bps == 8 && nchannels == 1:
for i := 0; i < n; i++ {
d.buf[i][0] = float64(int8(frame.Subframes[0].Samples[i])) / (1<<7 - 1)
d.buf[i][1] = float64(int8(frame.Subframes[0].Samples[i])) / (1<<7 - 1)
d.buf[i][0] = float64(int8(frame.Subframes[0].Samples[i])) * q
d.buf[i][1] = float64(int8(frame.Subframes[0].Samples[i])) * q
}
case bps == 16 && nchannels == 1:
for i := 0; i < n; i++ {
d.buf[i][0] = float64(int16(frame.Subframes[0].Samples[i])) / (1<<15 - 1)
d.buf[i][1] = float64(int16(frame.Subframes[0].Samples[i])) / (1<<15 - 1)
d.buf[i][0] = float64(int16(frame.Subframes[0].Samples[i])) * q
d.buf[i][1] = float64(int16(frame.Subframes[0].Samples[i])) * q
}
case bps == 24 && nchannels == 1:
for i := 0; i < n; i++ {
d.buf[i][0] = float64(int32(frame.Subframes[0].Samples[i])) / (1<<23 - 1)
d.buf[i][1] = float64(int32(frame.Subframes[0].Samples[i])) / (1<<23 - 1)
d.buf[i][0] = float64(int32(frame.Subframes[0].Samples[i])) * q
d.buf[i][1] = float64(int32(frame.Subframes[0].Samples[i])) * q
}
case bps == 8 && nchannels >= 2:
for i := 0; i < n; i++ {
d.buf[i][0] = float64(int8(frame.Subframes[0].Samples[i])) / (1<<7 - 1)
d.buf[i][1] = float64(int8(frame.Subframes[1].Samples[i])) / (1<<7 - 1)
d.buf[i][0] = float64(int8(frame.Subframes[0].Samples[i])) * q
d.buf[i][1] = float64(int8(frame.Subframes[1].Samples[i])) * q
}
case bps == 16 && nchannels >= 2:
for i := 0; i < n; i++ {
d.buf[i][0] = float64(int16(frame.Subframes[0].Samples[i])) / (1<<15 - 1)
d.buf[i][1] = float64(int16(frame.Subframes[1].Samples[i])) / (1<<15 - 1)
d.buf[i][0] = float64(int16(frame.Subframes[0].Samples[i])) * q
d.buf[i][1] = float64(int16(frame.Subframes[1].Samples[i])) * q
}
case bps == 24 && nchannels >= 2:
for i := 0; i < n; i++ {
d.buf[i][0] = float64(int32(frame.Subframes[0].Samples[i])) / (1<<23 - 1)
d.buf[i][1] = float64(int32(frame.Subframes[1].Samples[i])) / (1<<23 - 1)
d.buf[i][0] = float64(frame.Subframes[0].Samples[i]) * q
d.buf[i][1] = float64(frame.Subframes[1].Samples[i]) * q
}
default:
panic(fmt.Errorf("support for %d bits-per-sample and %d channels combination not yet implemented", bps, nchannels))
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