CGAL users discussion list

[Michael Hemmer <>]

From the manual:

Please note that the implementation of class /CGAL::Residue/ requires a 
mantissa precision according to the IEEE Standard for Floating-Point 
Arithmetic (IEEE 754). However, on some processors the traditional FPU 
uses an extended precision. Hence, it is indispensable that the proper 
mantissa length is enforced before performing any arithmetic operations. 
Moreover, it is required that numbers are rounded to the next nearest 
value. This can be ensured using /CGAL::Protect_FPU_rounding/ with 
/CGAL_FE_TONEAREST/, which also enforces the required precision as a 
side effect.

Setting this within each and every arithmetic operations would waste too 
much time.

And the lines in the Example:

 // Enforce IEEE double precision and rounding mode to nearest 
 // before useing modular arithmetic 
 CGAL::Protect_FPU_rounding<true> pfr(CGAL_FE_TONEAREST)


Michael Hemmer

Sanket Agarwal wrote:
> HI Guys,
>
> I am trying to use the Modular Arithmetic functionalities of the CGAL 
> package. Right now I am trying to familiarise myself with the code 
> structure. I am trying to compile/run the following code snippet:
>
> CGAL::Residue res(10);        // Initialising the object res of 
> residue class with the int constructor.
>
> I am being bumped up with the following error:
> -----------------------------------------------------------------------------------------------------
> terminate called after throwing an instance of 'CGAL::Assertion_exception'
>   what():  CGAL ERROR: assertion violation!
> Expr: FPU_get_cw() == CGAL_FE_TONEAREST
> File: /usr/local/include/CGAL/Modular_arithmetic/Residue_type.h
> Line: 110
> Aborted
> -----------------------------------------------------------------------------------------------------
>
> Residue_type.h:
> -----------------------------------------------------------------------------------------------------
> 106.   static inline
> 107.    double RES_round (double a){
> 108.     // call CGAL::Protect_FPU_rounding<true> pfr(CGAL_FE_TONEAREST)
> 109.      // before using modular arithmetic
> 110.      CGAL_assertion(FPU_get_cw() == CGAL_FE_TONEAREST);
> 111.      return ( (a + CST_CUT)  - CST_CUT);     
>     }
> -----------------------------------------------------------------------------------------------------
>
> Any pointers as to how I can correct this error ?