realbitprecision

Function: _def_realbitprecision
Class: default
Section: default
C-Name: sd_realbitprecision
Prototype:
Help:
Doc: the number of significant bits used to convert exact inputs given to
 transcendental functions (see \secref{se:trans}), or to create
 absolute floating point constants (input as \kbd{1.0} or \kbd{Pi} for
 instance). Unless you tamper with the \tet{format} default, this is also
 the number of significant bits used to print a \typ{REAL} number;
 \kbd{format} will override this latter behavior, and allow you to have a
 large internal precision while outputting few digits for instance.

 Note that most PARI's functions currently handle precision on a word basis (by
 increments of 32 or 64 bits), hence bit precision may be a little larger
 than the number of bits you expected. For instance to get 10 bits of
 precision, you need one word of precision which, on a 64-bit machine,
 correspond to 64 bits. To make things even more confusing, this internal bit
 accuracy is converted to decimal digits when printing floating point numbers:
 now 64 bits correspond to 19 printed decimal digits
 ($19 <  \log_{10}(2^{64}) < 20$).

 The value returned when typing \kbd{default(realbitprecision)} is the internal
 number of significant bits, not the number of printed decimal digits:
 \bprog
 ? default(realbitprecision, 10)
 ? \pb
       realbitprecision = 64 significant bits
 ? default(realbitprecision)
 %1 = 64
 ? \p
       realprecision = 3 significant digits
 ? default(realprecision)
 %2 = 19
 @eprog\noindent Note that \tet{realprecision} and \kbd{\bs p} allow
 to view and manipulate the internal precision in decimal digits.

 The default value is \kbd{128}, resp.~\kbd{96}, on a 64-bit, resp~.32-bit,
 machine.