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fix(fingerprint): prevent address overflow with bit masking

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- Scale and mask frequencies to 9 bits each
- Mask time delta to 14 bits
- Add sampleRate parameter to ExtractPeaks calls

Prevents hash collisions from bit overflow in fingerprint addresses.
This commit is contained in:
Chigozirim Igweamaka 2025-11-19 16:51:00 +01:00
parent e3a35ef1eb
commit 7104a1a7bc
1 changed files with 17 additions and 8 deletions
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25
server/shazam/fingerprint.go
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@ -26,7 +26,10 @@ func Fingerprint(peaks []Peak, songID uint32) map[uint32]models.Couple {
address := createAddress(anchor, target)
anchorTimeMs := uint32(anchor.Time * 1000)
fingerprints[address] = models.Couple{anchorTimeMs, songID}
fingerprints[address] = models.Couple{
AnchorTimeMs: anchorTimeMs,
SongID: songID,
}
}
}
@ -38,12 +41,18 @@ func Fingerprint(peaks []Peak, songID uint32) map[uint32]models.Couple {
// the anchor and target points, and other bits represent the time difference (delta time)
// between them. This function combines these components into a single address (a hash).
func createAddress(anchor, target Peak) uint32 {
anchorFreq := int(real(anchor.Freq))
targetFreq := int(real(target.Freq))
deltaMs := uint32((target.Time - anchor.Time) * 1000)
anchorFreqBin := uint32(anchor.Freq / 10) // Scale down to fit in 9 bits
targetFreqBin := uint32(target.Freq / 10)
// Combine the frequency of the anchor, target, and delta time into a 32-bit address
address := uint32(anchorFreq<<23) | uint32(targetFreq<<14) | deltaMs
deltaMsRaw := uint32((target.Time - anchor.Time) * 1000)
// Mask to fit within bit constraints
anchorFreqBits := anchorFreqBin & ((1 << maxFreqBits) - 1) // 9 bits
targetFreqBits := targetFreqBin & ((1 << maxFreqBits) - 1) // 9 bits
deltaBits := deltaMsRaw & ((1 << maxDeltaBits) - 1) // 14 bits (max ~16 seconds)
// Combine into 32-bit address
address := (anchorFreqBits << 23) | (targetFreqBits << 14) | deltaBits
return address
}
@ -66,7 +75,7 @@ func FingerprintAudio(songFilePath string, songID uint32) (map[uint32]models.Cou
return nil, fmt.Errorf("error creating spectrogram: %v", err)
}
peaks := ExtractPeaks(spectro, wavInfo.Duration)
peaks := ExtractPeaks(spectro, wavInfo.Duration, wavInfo.SampleRate)
utils.ExtendMap(fingerprint, Fingerprint(peaks, songID))
if wavInfo.Channels == 2 {
@ -75,7 +84,7 @@ func FingerprintAudio(songFilePath string, songID uint32) (map[uint32]models.Cou
return nil, fmt.Errorf("error creating spectrogram for right channel: %v", err)
}
peaks = ExtractPeaks(spectro, wavInfo.Duration)
peaks = ExtractPeaks(spectro, wavInfo.Duration, wavInfo.SampleRate)
utils.ExtendMap(fingerprint, Fingerprint(peaks, songID))
}