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The floating-point functions expect arguments of type mpfr_t.
The MPFR floating-point functions have an interface that is similar to the
GNU MP
functions. The function prefix for floating-point operations is mpfr_.
The user has to specify the precision of each variable. A computation that assigns a variable will take place with the precision of the assigned variable; the cost of that computation should not depend on the precision of variables used as input (on average).
The semantics of a calculation in MPFR is specified as follows: Compute the requested operation exactly (with “infinite accuracy”), and round the result to the precision of the destination variable, with the given rounding mode. The MPFR floating-point functions are intended to be a smooth extension of the IEEE 754 arithmetic. The results obtained on a given computer are identical to those obtained on a computer with a different word size, or with a different compiler or operating system.
MPFR does not keep track of the accuracy of a computation. This is left to the user or to a higher layer (for example, the MPFI library for interval arithmetic). As a consequence, if two variables are used to store only a few significant bits, and their product is stored in a variable with a large precision, then MPFR will still compute the result with full precision.
The value of the standard C macro errno may be set to non-zero after
calling any MPFR function or macro, whether or not there is an error. Except
when documented, MPFR will not set errno, but functions called by the
MPFR code (libc functions, memory allocator, etc.) may do so.
Next: API Compatibility, Previous: MPFR Basics, Up: GNU MPFR [Index]