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Worst LZMA compression on best compression level #731

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gix opened this issue Sep 22, 2023 · 2 comments · Fixed by #732
Closed

Worst LZMA compression on best compression level #731

gix opened this issue Sep 22, 2023 · 2 comments · Fixed by #732
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bug Bug lzma XZ compression format

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@gix
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gix commented Sep 22, 2023

Taken from mz_stream_lzma_set_prop_int64:

    case MZ_STREAM_PROP_COMPRESS_LEVEL:
        if (value >= 9)
            lzma->preset = LZMA_PRESET_EXTREME;
        else
            lzma->preset = LZMA_PRESET_DEFAULT;
        break;

Reading the xz-utils docs for the presets, and looking through its code, LZMA_PRESET_EXTREME is an extra flag on top of the compression level. Using it on its own is equal to using a compression level of 0, making MZ_COMPRESS_LEVEL_BEST result in the worst compression (and the other levels not doing anything). The level should probably be passed through, without using LZMA_PRESET_EXTREME at all.
@nmoinvaz
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Please consider making a PR. I don't use it on a regular basis.

gix added a commit to gix/minizip-ng that referenced this issue Sep 25, 2023
@gix
Fix lzma compression level zlib-ng#731
9c96447 
LZMA_PRESET_EXTREME is not a preset on its own but a flag which must be
used together with a level. The difference between level 9 with and without
the extreme flag also seems negligible, so this commit just passes through
the level and maps -1 and invalid values to the default preset.
@gix gix mentioned this issue Sep 25, 2023
Merged
nmoinvaz pushed a commit that referenced this issue Oct 19, 2023
@gix @nmoinvaz
Fix lzma compression level #731
26c484d 
LZMA_PRESET_EXTREME is not a preset on its own but a flag which must be
used together with a level. The difference between level 9 with and without
the extreme flag also seems negligible, so this commit just passes through
the level and maps -1 and invalid values to the default preset.
@nmoinvaz
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Merged into develop.

@nmoinvaz nmoinvaz added lzma XZ compression format bug Bug labels Oct 26, 2023
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Fix lzma compression level #731 gix/minizip-ng
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@gix @nmoinvaz