[FFmpeg-devel] [PATCH 8/9] dct-test: add 12 bit tests

Christophe Gisquet christophe.gisquet at gmail.com
Thu Oct 8 13:54:30 CEST 2015

2015-10-08 8:22 GMT+02:00 Christophe Gisquet <christophe.gisquet at gmail.com>:
> +SIC_WRAP(12)
> +
> +static const struct algo idct_tab12[] = {
> +    { "SIMPLE12-C",  simple_idct12_put_wrap,    FF_IDCT_PERM_NONE },
> +    { 0 }
> +};

Strange results are generated for it, and I don't know why (the C
version shouldn't overflow?). If I replace the current coeffs by their
x86 coeffs * 2 (like it is done for the 10 bits version to have a
bit-exact version), the issue no longer appears. I haven't verified if
the compiler plays a trick here by rescaling coefficients because
there's an undefined behaviour somewhere in the C.

I also don't know if there are codecs, beside jpeg, that would use
this 12bits version, and if there's an associated fate test:
fate-video, fate-vcodec and any test having jp in its name pass.


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