XL Fortran Enterprise Edition for AIX : User's Guide - IBM

$ cat fp_values.f
real plus_inf, minus_inf, plus_nanq, minus_nanq, nans
real large
data plus_inf /z’7f800000’/
data minus_inf /z’ff800000’/
data plus_nanq /z’7fc00000’/
data minus_nanq /z’ffc00000’/
data nans /z’7f800001’/
print *, ’Special values:’, plus_inf, minus_inf, plus_nanq, minus_nanq, nans
! They can also occur as the result of operations.
large = 10.0 ** 200
print *, ’Number too big for a REAL:’, large * large
print *, ’Number divided by zero:’, (-large) / 0.0
print *, ’Nonsensical results:’, plus_inf - plus_inf, sqrt(-large)
! To find if something is a NaN, compare it to itself.
print *, ’Does a quiet NaN equal itself:’, plus_nanq .eq. plus_nanq
print *, ’Does a signaling NaN equal itself:’, nans .eq. nans
! Only for a NaN is this comparison false.
end
$ xlf95 -o fp_values fp_values.f
** _main === End of Compilation 1 ===
1501-510 Compilation successful for file fp_values.f.
$ fp_values
Special values: INF -INF NaNQ -NaNQ NaNS
Number too big for a REAL: INF
Number divided by zero: -INF
Nonsensical results: NaNQ NaNQ
Does a quiet NaN equal itself: F
Does a signaling NaN equal itself: F
Exception-Handling Model
The IEEE standard defines several exception conditions that can occur:
OVERFLOW
The exponent of a value is too large to be represented.
UNDERFLOW
A nonzero value is so small that it cannot be represented without an
extraordinary loss of accuracy. The value can be represented only as zero
or a denormal number.
ZERODIVIDE
A finite nonzero value is divided by zero.
INVALID
Operations are performed on values for which the results are not defined.
These include:
v Operations on signaling NaN values
v infinity - infinity
v 0.0 * infinity
v 0.0 / 0.0
v mod(x,y) or ieee_rem(x,y) (or other remainder functions) when x is
infinite or y is zero
v
v
The square root of a negative number
Conversion of a floating point number to an integer when the converted
value cannot be represented faithfully
XL Fortran Floating-Point Processing 289