#209 Right channel decoding issue on clip with 32-bit build

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nobody
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2015-01-08
2014-06-13
Simon Kirby
No

x86 (32-bit) build of 1.18.0, 1.19.0, 1.20.0, svn snapshot seems to incorrectly decode the attached mp3 snippet. At the point where the right channel is expected to clip (typical), the output waveform seems to jump back to 0(?) instead, and it sounds like static. configure --with-cpu=i486. Noticed originally with 1.18.0-1 in Debian sid. On my amd64 machines, and with other decoders (exculding mplayer), everything is fine.

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Discussion

  • Thomas Orgis
    Thomas Orgis
    2014-06-14

    Am Fri, 13 Jun 2014 22:51:37 +0000
    schrieb "Simon Kirby" sim@users.sf.net:

    configure --with-cpu=i486

    To clarify: This only happens with --with-cpu=i486, right? Choosing
    --with-cpu=i386 is fine? Point being, i486 is special code for the
    Intel 486 CPU. It is different from all other decoders. It is not for
    any x86 CPU. It's a special hack to get the best out of that class of
    CPU. Nevertheless, it still should work correctly, but I admit I'll
    have to check if there is any attempt at proper clipping at all in that
    code path. It's a bonus over basic decoding, after all.

    Alrighty then,

    Thomas

     
  • Simon Kirby
    Simon Kirby
    2014-06-14

    Confirmed that the problem only happens with --with-cpu=i486. --with-cpu=i386 seems to decode properly. The bug may not be exactly as I describe -- I'm just guessing -- but it sure is easy to hear from that snippet. Cheers!

     
  • Thomas Orgis
    Thomas Orgis
    2015-01-08

    Just a note that I'm still there ... I must admit that the bug went under for some time. I still need to check if hacking in proper clipping (not jumping around) sensible with the i486 code. Actually ... I'd have to dig out a real 486 CPU to check implications of any change. One point for current use is really that you are not supposed to use the 486 decoder unless you really intend to run it on a 486 CPU.