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fix(par2): skip PAR2 creation for files smaller than SIMD alignment #213

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Merged
javi11 merged 1 commit into from
Apr 25, 2026
+6 −9
Merged

fix(par2): skip PAR2 creation for files smaller than SIMD alignment #213

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15 changes: 6 additions & 9 deletions internal/par2/par2.go
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Original file line number Diff line number Diff line change
Expand Up @@ -218,18 +218,15 @@ func (p *NativeExecutor) createPar2ForFile(ctx context.Context, file fileinfo.Fi
// clamping to prevent buffer overreads and segfaults.
if file.Size > 0 && parBlockSize > file.Size {
const simdSafeAlignment = uint64(128)
if file.Size >= simdSafeAlignment {
parBlockSize = (file.Size / simdSafeAlignment) * simdSafeAlignment
} else {
// File too small for 128-byte alignment; round to nearest multiple of 4 (PAR2 spec)
parBlockSize = (file.Size / 4) * 4
}
if parBlockSize < 4 {
// File is smaller than minimum valid PAR2 slice size — skip creation
slog.WarnContext(ctx, "File too small for PAR2 creation, skipping",
if file.Size < simdSafeAlignment {
// File smaller than SIMD-safe alignment — par2go's C backend may read
// past the buffer end with sub-stride slice sizes, causing a segfault
// on AVX-512 hardware. Skip PAR2 creation for such tiny files.
slog.WarnContext(ctx, "File too small for SIMD-safe PAR2 creation, skipping",
"path", file.Path, "size", file.Size)
return nil, nil
}
parBlockSize = (file.Size / simdSafeAlignment) * simdSafeAlignment
}
// PAR2 spec requires slice size to be a multiple of 4
parBlockSize = alignDown(parBlockSize, 4)
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