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ALTFP_SINCOS - cosine mode

Honored Contributor II

I'm running Quartus 11.0sp1 


I think I found an error for the ALTFP_SINCOS megafunction in cosine mode. 


For negative inputs the result comes out with the wrong sign. 


Example: cos(-0.1) = -0.995. 


Since cosine is an even function i.e., cos(x) = cos(-x) it is not that hard to workaround this problem.  



I have a question about the workaround/fix (solution id: rd12212011_626) for the ALTFP_SINCOS megafunction in sine mode. 


To workaround this, change the <altfp_sincos_variant_file_name>.vhd file, line 22850 as follows: 

Change from: 

wire_mantissanorm_add_datab <= ( "0000000000000000000000" & mantissanormnode_w(12)); 

Change to: 

wire_mantissanorm_add_datab <= ( "0000000000000000000000" & mantissanormnode_w(11)); 


Am I supposed to make the same change in cosine mode? 



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Honored Contributor II

How do you get 0.1 into ALTFP_SINCOS?  

I try it with declaration  

real rho = 0.1; 

But ALTFP_SINCOS cannot accept with real number. 

Thanks for your reading, waiting for your reply!