faq.txt

来自「这是一个LINUX环境的 VDR 插件源代码,可支持Irdeto, Seca, 」· 文本 代码 · 共 78 行

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FFdecsa
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FFdecsa is a fast implementation of the CSA decryption algorithm for MPEG
TS packets.

Q: What does FF stands for?
A: FFdecsa means "Fucking Fast decsa".

Q: Why would you use such a rude name?
A: Because this code is fucking fast, more than 800% the speed of the best
   implementation I'm able to find around at the moment.

Q: How it that possible? Are all other programmers stupid?
A: No, they just tried to save a cycle or two tweaking a fundamentally wrong
   implementation. The algorithm has to be implemented in a totally different
   way to achieve good speed.

Q: Do you use multimedia instructions?
A: I use every trick I could come up with, including multimedia instructions.
   They are not fundamental in achieving speed, a version without them runs
   at 6x the speed of the best implementation around (which uses MMX).

Q: So how did you do that?
A: By using a different approach for the implementation. This code is not
   exploiting some new CSA vulnerability, it is just doing the same
   calculations better. Think about replacing bubble sort with quick sort.

Q: You're joking, it's impossible to gain so much speed.
A: Speed test are available, technical documentation is available, source
   code is available. Try it yourself.
   If you want details, these are some of the documented tricks I used
   (more details in the docs directory):
    TRICK NUMBER 0: emulate the hardware
    TRICK NUMBER 1: virtual shift registers
    TRICK NUMBER 2: parallel bitslice
    TRICK NUMBER 3: multimedia instructions
    TRICK NUMBER 4: parallel byteslice
    TRICK NUMBER 5: efficient bit permutation
    TRICK NUMBER 6: efficient normal<->slice conversion
    TRICK NUMBER 7: try hard to process packets together
    TRICK NUMBER 8: try to avoid doing the same thing many times
    TRICK NUMBER 9: compiler
    TRICK NUMBER a: a lot of brain work

Q: How can be this code useful?
A: You can use this code in place of the old slow implementations and save a
   lot of CPU power.

Q: Just that?
A: Well, new applications are possible.
   Decrypting a whole transponder is easily doable now. Well, a $50 CPU can
   decrypt four transponder at the same time if you have four DVB boards (but
   I couldn't test that).

Q: You're cheating, this code is fake, I don't believe one word.
A: Go away. This is technical stuff for people with brains.

Q: This code is great, may I distribute your code in original or modified
   form?
A: Only if you respect the license.

Q: May I use your code in my player/library/plugin...?
A: Again, you have to respect the license.

Q: Are you an extraterrestrial programmer?
A: No, just a Turkish guy with a PC to play with :-)

Q: Why did you spend your time doing this?
A: Because I thought that my approach was doable and I was sure it would
   have been much faster, so I had to implement it to confirm I was right.
   I got 8x the speed and that's enough to be proud of it. And I could not
   just keep the code for myself only.

Q: What is the answer to the meaning of the universe?
A: 42,43,71,5f,65,85,f6,76,0d,13,28,96,...