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campo85

Fixed point and quantization mode

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Hi all,

I'm using the SystemC fixed point type (sc_fixed) in one of the modules in my project. This module has to cope with some complex operation ( mainly multiplications and divisions). As you know, when a sc_fixed variable is instantiated I can choose what type of quantization I want among the several available. I've seen that the SC_RND is the one that gives me the better result compared with the same arithmetic but implemented in pure C++ (floating point). I guess that from an hardware point of view the SC_RND is more complicated to implement and slower than for example a SC_TRN. Does anyone knows how big is the drop in terms of timing closure ? Or does anyone know how each quantization mode is implemented in hardware ? I can figure out how the SC_TRN and SC_TRN_ZERO are implemented, but the others are a mistery. Thanks for any reply.

 

Cheers.

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Hi, 

For rounding, take the deleted bits, add the msb of that to the value. 

If you want to know how all the specs for all rounding modes, please refer to table 46 in IEEE1666-2011 standard. 

regards, Fred

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