Topic : RC51 - arithmetic library - slow 32bit division

Forum : 8051

Original Post
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May 23, 2007 - 4:45pm
Guest

Signed 32bit (long) division is the slowest basic calculation for most compilers. However, in RC51 I'm surprised at how much slower it is than other operations. The call C_SLDIV_SP takes typically 2200 machine cycles. That's 100usec on a 22MHz single-cycle 8051. By comparsion 16bit division e.g C_UIDIV, takes roughly 60 cycles.

Is the time for C_SLDIV_SP reasonable? For now I have to beware of using it in some signal processing paths. This is the one routine whose optimisation, it that's possible, would help me most.

Thanks Steven Pruzina
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May 23, 2007 - 7:10pm
Guest

if you have a problem with the time it takes to do 32 bit operations, you should not have selected a 8 bit processor.

Erik
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May 23, 2007 - 7:21pm
Guest

Hi Erik

Well... hindsight is always 20:20. Also, Silicon Labs remain a good fit for my application overall. The slow 32bit divide isn't a killer; I'm just asking Raisonance if it is unreasonably long relative to the other arithmetic operations in their library.

Steven
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May 23, 2007 - 8:06pm
Guest

2200 machine cycles. . By comparsion 16bit division e.g C_UIDIV, takes roughly 60 cycles.

well 60 squared is 3600, so 2000 sounds great

Erik