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When an expression requires the use of temporary intermediate mpf_class
values, like f=g*h+x*y
, those temporaries will have the same precision
as the destination f
. Explicit constructors can be used if this
doesn’t suit.
Construct an mpf_class
. Any standard C++ type can be used, except
long long
and long double
, and any of the GMP C++ classes can be
used.
If prec is given, the initial precision is that value, in bits. If
prec is not given, then the initial precision is determined by the type
of op given. An mpz_class
, mpq_class
, or C++
builtin type will give the default mpf
precision (see Initializing Floats). An mpf_class
or expression will give the precision of that
value. The precision of a binary expression is the higher of the two
operands.
mpf_class f(1.5); // default precision mpf_class f(1.5, 500); // 500 bits (at least) mpf_class f(x); // precision of x mpf_class f(abs(x)); // precision of x mpf_class f(-g, 1000); // 1000 bits (at least) mpf_class f(x+y); // greater of precisions of x and y
Construct an mpf_class
from an mpf_t
. The value in f is
copied into the new mpf_class
, there won’t be any permanent association
between it and f.
If prec is given, the initial precision is that value, in bits. If prec is not given, then the initial precision is that of f.
Construct an mpf_class
converted from a string using mpf_set_str
(see Assigning Floats). If prec is given, the initial precision is
that value, in bits. If not, the default mpf
precision
(see Initializing Floats) is used.
If the string is not a valid float, an std::invalid_argument
exception
is thrown. The same applies to operator=
.
With C++11 compilers, floats can be constructed with the syntax
1.23e-1_mpf
which is equivalent to mpf_class("1.23e-1")
.
Convert and store the given op value to an mpf_class
object. The
same types are accepted as for the constructors above.
Note that operator=
only stores a new value, it doesn’t copy or change
the precision of the destination, instead the value is truncated if necessary.
This is the same as mpf_set
etc. Note in particular this means for
mpf_class
a copy constructor is not the same as a default constructor
plus assignment.
mpf_class x (y); // x created with precision of y mpf_class x; // x created with default precision x = y; // value truncated to that precision
Applications using templated code may need to be careful about the assumptions
the code makes in this area, when working with mpf_class
values of
various different or non-default precisions. For instance implementations of
the standard complex
template have been seen in both styles above,
though of course complex
is normally only actually specified for use
with the builtin float types.
These functions provide a C++ class interface to the corresponding GMP C routines.
cmp
can be used with any of the classes or the standard C++ types,
except long long
and long double
.
The accuracy provided by hypot
is not currently guaranteed.
Get or set the current precision of an mpf_class
.
The restrictions described for mpf_set_prec_raw
(see Initializing Floats) apply to mpf_class::set_prec_raw
. Note in particular that the
mpf_class
must be restored to it’s allocated precision before being
destroyed. This must be done by application code, there’s no automatic
mechanism for it.
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