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Set the default precision to be at least prec bits. All
subsequent calls to mpf_init
will use this precision, but previously
initialized variables are unaffected.
Return the default precision actually used.
An mpf_t
object must be initialized before storing the first value in
it. The functions mpf_init
and mpf_init2
are used for that
purpose.
Initialize x to 0. Normally, a variable should be initialized once only
or at least be cleared, using mpf_clear
, between initializations. The
precision of x is undefined unless a default precision has already been
established by a call to mpf_set_default_prec
.
Initialize x to 0 and set its precision to be at least
prec bits. Normally, a variable should be initialized once only or at
least be cleared, using mpf_clear
, between initializations.
Initialize a NULL-terminated list of mpf_t
variables, and set their
values to 0. The precision of the initialized variables is undefined unless a
default precision has already been established by a call to
mpf_set_default_prec
.
Free the space occupied by x. Make sure to call this function for all
mpf_t
variables when you are done with them.
Free the space occupied by a NULL-terminated list of mpf_t
variables.
Here is an example on how to initialize floating-point variables:
{ mpf_t x, y; mpf_init (x); /* use default precision */ mpf_init2 (y, 256); /* precision at least 256 bits */ … /* Unless the program is about to exit, do ... */ mpf_clear (x); mpf_clear (y); }
The following three functions are useful for changing the precision during a calculation. A typical use would be for adjusting the precision gradually in iterative algorithms like Newton-Raphson, making the computation precision closely match the actual accurate part of the numbers.
Return the current precision of op, in bits.
Set the precision of rop to be at least prec bits. The value in rop will be truncated to the new precision.
This function requires a call to realloc
, and so should not be used in
a tight loop.
Set the precision of rop to be at least prec bits, without changing the memory allocated.
prec must be no more than the allocated precision for rop, that
being the precision when rop was initialized, or in the most recent
mpf_set_prec
.
The value in rop is unchanged, and in particular if it had a higher precision than prec it will retain that higher precision. New values written to rop will use the new prec.
Before calling mpf_clear
or the full mpf_set_prec
, another
mpf_set_prec_raw
call must be made to restore rop to its original
allocated precision. Failing to do so will have unpredictable results.
mpf_get_prec
can be used before mpf_set_prec_raw
to get the
original allocated precision. After mpf_set_prec_raw
it reflects the
prec value set.
mpf_set_prec_raw
is an efficient way to use an mpf_t
variable at
different precisions during a calculation, perhaps to gradually increase
precision in an iteration, or just to use various different precisions for
different purposes during a calculation.
Next: Assigning Floats, Previous: Floating-point Functions, Up: Floating-point Functions [Index]