Playback inaccuracies

[9001]

Gave it a spin with some tricky songs, and unfortunately I noticed some bugs that also appear in several other player libs. Note that it might be the songs that are at fault, with certain libs (xmplay/bassmod, openmpt/modplug, milkytracker/milkyplay) taking steps to cover it up. I don't know enough about the file format to judge.
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binary_world.xm goes bad 39sec in, and OpenMPT has slight issues too
http://modarchive.org/module.php?138953
http://clyp.it/hhp3pfex
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around 51sec, the lead echo in colond.xm is played at a slightly different pitch than the main lead, resulting in phasing
http://modarchive.org/module.php?174415
http://clyp.it/gfuaa1do
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as jt_strng.xm hits the higher notes at 35sec, they go off-pitch.
libxm gets a fair bit of static as well but I suppose that's intended
http://modarchive.org/module.php?46508
http://clyp.it/nh15rq5h
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synthetic_attack.xm plays correctly but segfaults at the end: (fixed in ac0bbdb, the module file is unsane. Opening then resaving the module in MilkyTracker fixes it.)
http://modarchive.org/module.php?142503
^{#0 xm_row (ctx=0x7f8d92832010, output=, numsamples=128) at /libxm-master/src/play.c:847
#1 xm_tick (ctx=0x7f8d92832010, output=, numsamples=128) at /libxm-master/src/play.c:948
#2 xm_sample (ctx=0x7f8d92832010, output=, numsamples=128) at /libxm-master/src/play.c:1293
#3 xm_generate_samples (ctx=0x7f8d92832010, output=, numsamples=128) at /libxm-master/src/play.c:1340}

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zalza-tequila_groove.xm throws assertion failures, (fixed in f24bcab)
and some static at the 49sec and 58sec marks:
http://modarchive.org/module.php?66518
^{xm_sample(): final sample value is 136597905678638606450688.000000, this is a bug
xm_sample(): final sample value is 296616456960244306673664.000000, this is a bug
xm_sample(): final sample value is 144714319948683478564864.000000, this is a bug}
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All tests done with master as of writing.
Also, what are those (*) in the effects table?

[Artefact2]

Thanks for submitting these problematic modules. I use Milkytracker as a reference so if these sound different there are definitely bugs in libxm.

The * in the effects table mean they remember the last nonzero parameter. It came from the original table but I should remove it in the readme.

[Artefact2]

Found another one: aurora_dawn.xm. The tone portamento in the intro is wrong. (fixed in 467d312)

[Artefact2]

jt_strng.xm playback has been fixed as of 013d814. Thanks @rasky

[Artefact2]

colond.xm phasing has been fixed as of 21144fc. Thanks @rasky again!