[vorbis-dev] Libvorbis suggestion & floating point exception

[Jan Lellmann]

Hello,

I'm not quite sure if this is the right list for my questions, please excuse
if it isn't.

1. While using vorbislib (Win2K/Borland C++ Builder 5), I'm getting
reproducible floating point exceptions at lots of sample rate/bit rate
combinations. For example, the original encoder_example.c, with just the
initialization line changed to

  vorbis_encode_init(&vi,2,22050,48000,48000,48000);

generates a "floating point exception 0xc0000090" in psy.c /
bark_noise_hybridmp (line 642).
The code reads:

    D = tN * tXX - tX * tX;
    R = (A + fi * B) / D;

Before the crash, tXX and tX are both 0, thus D == 0. This causes a "divide
by zero".
As said, it is reproducible every single time. At higher sample rates it
works at 48kbps, but crashes at higher bit rates. I tested the 1.0 build
(static as well as the pre-built DLL from the distribution) and the CVS
snapshot, same result.

However, at 44.1kHz all bit rates seem to work.

Any ideas?

<p>2. In vorbisenc.c / vorbis_encode_setup_managed, there's a piece that reads:

  if(nominal_bitrate<=0.){
    if(max_bitrate>0.){
      nominal_bitrate=max_bitrate*.875;
    }else{  ...

If only min_bitrate and max_bitrate are passed, and nominal_bitrate set to
zero for "auto" mode, nominal_bitrate might actually end lower than
min_bitrate (e.g. if min_bitrate == max_bitrate for "CBR" emulation).

I think it should be something like:

  if(nominal_bitrate<=0.){
    if(max_bitrate>0.){
      nominal_bitrate=max(min_bitrate, max_bitrate*.875);
    }else{  ...

Greetings,
  Jan

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