gawk uses the GNU MPFR library
for arbitrary precision floating-point arithmetic. The MPFR library
provides precise control over precisions and rounding modes, and gives
correctly rounded, reproducible, platform-independent results. With one
of the command-line options --bignum or -M,
all floating-point arithmetic operators and numeric functions can yield
results to any desired precision level supported by MPFR.
Two built-in variables,
provide control over the working precision and the rounding mode
(see Setting Precision, and
see Setting Rounding Mode).
The precision and the rounding mode are set globally for every operation
The default working precision for arbitrary precision floating-point values is
53 bits, and the default value for
which selects the IEEE-754
roundTiesToEven rounding mode
(see Rounding Mode).1
gawk uses the default exponent range in MPFR
(emax = 2^30 − 1, emin = −emax)
for all floating-point contexts.
There is no explicit mechanism to adjust the exponent range.
MPFR does not implement subnormal numbers by default,
and this behavior cannot be changed in gawk.
NOTE: When emulating an IEEE-754 format (see Setting Precision), gawk internally adjusts the exponent range to the value defined for the format and also performs computations needed for gradual underflow (subnormal numbers).
NOTE: MPFR numbers are variable-size entities, consuming only as much space as needed to store the significant digits. Since the performance using MPFR numbers pales in comparison to doing arithmetic using the underlying machine types, you should consider using only as much precision as needed by your program.
default precision is 53 bits, since according to the MPFR documentation,
the library should be able to exactly reproduce all computations with
double-precision machine floating-point numbers (
in C), except the default exponent range is much wider and subnormal
numbers are not implemented.