what's look-up table?

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ash

Joined: 25 Dec 2002
Posts: 160
Location: Europe

31 Aug 2003 15:25 what's look-up table?

Hi All,
I can write many applications without using look-up tables, but in deep what are them?

mowgli

Joined: 05 Apr 2002
Posts: 142
Helped: 20

01 Sep 2003 7:31 Look up table

A look up table (LUT) is simply a matrix (mainly stored in a memory) which holds same values of complex functions (e.g. sine table). It is used to avoid complex calculation of these values where this would be too onerous for hardware or processor speed. In this way these values are simply addressed in some way and the calculation costs "only" one or more access in memory.
Hope this will be useful for you.
Mowgli

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vfone

Joined: 10 Oct 2001
Posts: 2328
Helped: 327

01 Sep 2003 8:10 Example of look-up table

As an example of look-up table; in GSM you have each point of the shape of the burst stored in memory. This shape should be very well defined because it will influence the performance in TX mode. So the system before each burst transmission, just have to call this numbers from the memory (look-up table).
Regards

artem

Joined: 22 May 2003
Posts: 1652
Helped: 91
Location: Turan

03 Sep 2003 16:09

Lookup tables are particular implementation related to generic data structures . Let say tree's or linked lists . Some program do not require using data structures , but for complex programs dealing with referenced data carefull data structure selection and design is preferred . This will define code quality and performance .