Technical data

Cray Standard C/C++ Reference Manual
10.1.2.6.1 Cray floating-point Representation
Types float and double represent Cray single-precision (64-bit) floating-point
values; long double represents Cray double-precision (128-bit) floating-point
values.
An integral number that is converted to a floating-point number that cannot
exactly represent the original value is truncated toward 0. A floating-point
number that is converted to a narrower floating-point number is also truncated
toward 0.
Floating-point arithmetic depends on implementation-defined ranges for types of
data. The values of the minimums and maximums for these ranges are defined
by macros in the standard header file float.h. All floating-point operations on
operands that are within the defined range yield results that are also in this range
if the true mathematical result is in the range. The results are accurate to within
the ability of the hardware to represent the true value.
The maximum positive value for types float, double, and long double is
approximately as follows:
2.7 × 10
2456
Several math functions return this upper limit if the true value equals or exceeds
it.
The minimum positive value for types float, double, and long double is
approximately as follows:
3.67 × 10
-2466
These numbers define a range that is slightly smaller than the value that can be
represented on a UNICOS or UNICOS/mk system, but use of numbers outside
this range may not yield predictable results. For exact values, use the values
defined in the header file, float.h.
A floating-point value, when rounded off, can be accurately represented
to approximately 14 decimal places for types float and double, and to
approximately 28 decimal places for type long double as determined by the
following equation:
(10.1)
146 S–2179–36