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Old 25 February 2017, 13:46   #1
bloodline
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LVO tables in exec libraries

Does anyone know why the lvo tables are constructed as a list of JMP <address> instructions rather than just a simple list of pointers?

That would have saved 2bytes per entry, is there any advantage to the JMP approach?
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Old 25 February 2017, 14:12   #2
Leffmann
 
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The advantage is that the function call becomes shorter, a single instruction on 68000 and 68010. If you had just stored an array of pointers you would've needed one more instruction of 2 bytes and one temporary address register per call on 68000 on 68010.

I don't know how many library and device functions are active on a typical Workbench installation, a thousand maybe, so the savings would've been just a couple of kilobytes, minus the above cost for all the software.
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Old 25 February 2017, 15:35   #3
bloodline
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Quote:
Originally Posted by Leffmann View Post
The advantage is that the function call becomes shorter, a single instruction on 68000 and 68010. If you had just stored an array of pointers you would've needed one more instruction of 2 bytes and one temporary address register per call on 68000 on 68010.

I don't know how many library and device functions are active on a typical Workbench installation, a thousand maybe, so the savings would've been just a couple of kilobytes, minus the above cost for all the software.
Good call. Many thanks
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