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some words about required mantissa length refering to CGAL::Protect_FPU_rounding

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Michael Hemmer
2008-12-01 15:00:35 +00:00
parent b874b6b77c
commit 2fe69c4c8d
2 changed files with 13 additions and 10 deletions
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Modular_arithmetic/doc_tex/Modular_arithmetic_ref/Residue.tex
+7 -5
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@@ -17,11 +17,13 @@ old prime and can be reused after restoring the old prime.
Since the type is based on double
arithmetic the prime is restricted to values less than $2^{26}$.
The initial value of $p$ is 67111067.
Moreover, the implementation of class \ccc{CGAL::Residue} requires that
doubles are rounded to nearest, that is, it indispensable that the
rounding mode is set accordingly before performing any arithmetic operations.
For instance you may use \ccc{CGAL::Protect_FPU_rounding} with
\ccc{CGAL_FE_TONEAREST}.
Please note that the implementation of class \ccc{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. For instance you may use \ccc{CGAL::Protect_FPU_rounding} with
\ccc{CGAL_FE_TONEAREST}, which enforces the required precision as a side effect.
In case the flag \ccc{CGAL_HAS_THREADS}
is undefined the prime is just stored in a static member