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These functions assign new values to already initialized floats (see Initialization Functions).
Set the value of rop from op, rounded
toward the given direction rnd.
Note that the input 0 is converted to +0 by mpfr_set_ui,
mpfr_set_si, mpfr_set_uj, mpfr_set_sj,
mpfr_set_z, mpfr_set_q and
mpfr_set_f, regardless of the rounding mode.
If the system does not support the IEEE 754 standard,
mpfr_set_flt, mpfr_set_d, mpfr_set_ld and
mpfr_set_decimal64 might not preserve the signed zeros.
The mpfr_set_decimal64 function is built only with the configure
option ‘--enable-decimal-float’, which also requires
‘--with-gmp-build’, and when the compiler or
system provides the ‘_Decimal64’ data type
(recent versions of GCC support this data type);
to use mpfr_set_decimal64, one should define the macro
MPFR_WANT_DECIMAL_FLOATS before including mpfr.h.
mpfr_set_q might fail if the numerator (or the
denominator) can not be represented as a mpfr_t.
Note: If you want to store a floating-point constant to a mpfr_t,
you should use mpfr_set_str (or one of the MPFR constant functions,
such as mpfr_const_pi for Pi) instead of
mpfr_set_flt, mpfr_set_d,
mpfr_set_ld or mpfr_set_decimal64.
Otherwise the floating-point constant will be first
converted into a reduced-precision (e.g., 53-bit) binary
(or decimal, for mpfr_set_decimal64) number before
MPFR can work with it.
Set the value of rop from op multiplied by two to the power e, rounded toward the given direction rnd. Note that the input 0 is converted to +0.
Set rop to the value of the string s in base base,
rounded in the direction rnd.
See the documentation of mpfr_strtofr for a detailed description
of the valid string formats.
Contrary to mpfr_strtofr, mpfr_set_str requires the
whole string to represent a valid floating-point number.
The meaning of the return value differs from other MPFR functions:
it is 0 if the entire string up to the final null character
is a valid number in base base; otherwise it is −1, and
rop may have changed (users interested in the ternary value
should use mpfr_strtofr instead).
Note: it is preferable to use mpfr_strtofr if one wants to distinguish
between an infinite rop value coming from an infinite s or from
an overflow.
Read a floating-point number from a string nptr in base base,
rounded in the direction rnd; base must be either 0 (to
detect the base, as described below) or a number from 2 to 62 (otherwise
the behavior is undefined). If nptr starts with valid data, the
result is stored in rop and *endptr points to the
character just after the valid data (if endptr is not a null pointer);
otherwise rop is set to zero (for consistency with strtod)
and the value of nptr is stored
in the location referenced by endptr (if endptr is not a null
pointer). The usual ternary value is returned.
Parsing follows the standard C strtod function with some extensions.
After optional leading whitespace, one has a subject sequence consisting of an
optional sign (+ or -), and either numeric data or special
data. The subject sequence is defined as the longest initial subsequence of
the input string, starting with the first non-whitespace character, that is of
the expected form.
The form of numeric data is a non-empty sequence of significand digits with an
optional decimal point, and an optional exponent consisting of an exponent
prefix followed by an optional sign and a non-empty sequence of decimal
digits. A significand digit is either a decimal digit or a Latin letter (62
possible characters), with A = 10, B = 11, …, Z =
35; case is ignored in bases less or equal to 36, in bases larger than 36,
a = 36, b = 37, …, z = 61.
The value of a
significand digit must be strictly less than the base. The decimal point can
be either the one defined by the current locale or the period (the first one
is accepted for consistency with the C standard and the practice, the second
one is accepted to allow the programmer to provide MPFR numbers from strings
in a way that does not depend on the current locale).
The exponent prefix can be e or E for bases up to 10, or
@ in any base; it indicates a multiplication by a power of the
base. In bases 2 and 16, the exponent prefix can also be p or P,
in which case the exponent, called binary exponent, indicates a
multiplication by a power of 2 instead of the base (there is a difference
only for base 16); in base 16 for example 1p2 represents 4 whereas
1@2 represents 256. The value of an exponent is always written in
base 10.
If the argument base is 0, then the base is automatically detected
as follows. If the significand starts with 0b or 0B, base 2
is assumed. If the significand starts with 0x or 0X, base 16
is assumed. Otherwise base 10 is assumed.
Note: The exponent (if present)
must contain at least a digit. Otherwise the possible
exponent prefix and sign are not part of the number (which ends with the
significand). Similarly, if 0b, 0B, 0x or 0X
is not followed by a binary/hexadecimal digit, then the subject sequence
stops at the character 0, thus 0 is read.
Special data (for infinities and NaN) can be @inf@ or
@nan@(n-char-sequence-opt), and if base <= 16,
it can also be infinity, inf, nan or
nan(n-char-sequence-opt), all case insensitive.
A n-char-sequence-opt is a possibly empty string containing only digits,
Latin letters and the underscore (0, 1, 2, …, 9, a, b, …, z,
A, B, …, Z, _). Note: one has an optional sign for all data, even
NaN.
For example, -@nAn@(This_Is_Not_17) is a valid representation for NaN
in base 17.
Set the variable x to NaN (Not-a-Number), infinity or zero respectively.
In mpfr_set_inf or mpfr_set_zero, x is set to plus
infinity or plus zero iff sign is nonnegative;
in mpfr_set_nan, the sign bit of the result is unspecified.
Swap the structures pointed to by x and y. In particular,
the values are exchanged without rounding (this may be different from
three mpfr_set calls using a third auxiliary variable).
Warning! Since the precisions are exchanged, this will affect future
assignments. Moreover, since the significand pointers are also exchanged,
you must not use this function if the allocation method used for x
and/or y does not permit it. This is the case when x and/or
y were declared and initialized with MPFR_DECL_INIT, and
possibly with mpfr_custom_init_set (see Custom Interface).
Next: Combined Initialization and Assignment Functions, Previous: Initialization Functions, Up: MPFR Interface [Index]