[vorbis-dev] slightly different audio output

[Pattara Kiatisevi]

On Wed, 10 Apr 2002, Segher Boessenkool wrote:

> >   magic.whole = ((long long)x * (long long) y) >> TRIGBITS;
> >   return magic.halves.lo;
>
> Use
>
> (blabla + (1 << (TRIGBITS-1))) >> TRIGBITS
>
>
> This is not as inefficient as it looks, given appropriate
> tricks (and appropriate cpu architecture!).

Hmm, I tried it and didn't find much improvement on the accuracy though.
Here are the results of int with rounding/int without rounding/float
respectively.

rai16:~/cvs/oggonachip/software/vorbis/libvorbis-linux$ tail
audioout-int-30bit-mdct-rounding.txt
0290670 024c 0844 02e6 088d 0358 08b2 0399 086e
0290680 03aa 07dc 03a2 0739 03c0 06c2 0444 069a
0290690 04e4 0655 0593 05f6 069b 05c0 0794 057a
02906a0 0863 052d 0955 0509 0a3a 04f5 0b01 04dd
02906b0 0bc2 050a 0c9c 055b 0d43 059c 0dd3 05e7
02906c0 0e87 066c 0f7e 0740 1031 07da 108f 0821
02906d0 1117 0892 1195 091a 11e4 098a 124e 0a14
02906e0 12c8 0a96 134c 0aeb 13db 0b30 1430 0b0c
02906f0 1469 0a85 1480 09ca 1480 08d2 1471 07c7
0290700

rai16:~/cvs/oggonachip/software/vorbis/libvorbis-linux$ tail
audioout-int-30bit-mdct.txt
0290670 025e 085f 02ce 0896 034a 08b2 039d 087a
0290680 03ac 07df 03a0 073a 03de 06d7 0458 06a1
0290690 04f5 066b 05c2 061a 069e 05cc 0785 057b
02906a0 0865 052d 095e 050c 0a47 04f1 0b0e 04f1
02906b0 0bd2 0503 0c9e 054f 0d4a 059d 0dd6 05e8
02906c0 0e88 0672 0f79 0742 1046 07ec 10b1 083d
02906d0 1112 0896 1190 0928 11e5 09a5 1244 0a16
02906e0 12f9 0ab6 1395 0b16 13f5 0b37 144d 0b21
02906f0 149c 0ab9 14aa 09e7 150b 0939 14a5 07fd
0290700

rai16:~/cvs/oggonachip/software/vorbis/libvorbis-linux$ tail
audioout-float.txt
0290670 0262 0860 02ee 08a1 0377 08c5 03bc 0884
0290680 03c7 07ea 03be 073c 03d8 06c0 0459 0697
0290690 0506 0664 05bf 0606 06bd 05c6 07b6 0583
02906a0 0883 0528 097d 0505 0a71 04f9 0b23 04dc
02906b0 0beb 0502 0cc6 0564 0d6b 05aa 0df6 05eb
02906c0 0eb4 067a 0fad 0754 1072 07f8 10da 0846
02906d0 114e 08b1 11c8 093f 121c 09b8 128d 0a3d
02906e0 1318 0ac0 1396 0b20 141d 0b5e 1477 0b3c
02906f0 14a0 0aaf 14d1 09f1 14cb 08ed 14a4 07dd
0290700

Regards,
Pattara

>
>
> Segher
>
>
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