IEEE Formats

(The material in this appendix is adapted from the IEEE-754 (1985) floating point standard. It is not intended to be a comprehensive description of the IEEE formats; readers should refer to the IEEE standard.)

FITS recognizes all IEEE basic formats, including the special values. Table B.1 shows the type of IEEE floating point value, regular or special, for all double and single precision hexadecimal byte patterns.

Table B.1: IEEE Floating Point Formats

IEEE value	Double Precision	Single Precision
$+0$	0000000000000000	00000000
denormalized	0000000000000001	00000001
	to	to
	000FFFFFFFFFFFFF	007FFFFF
positive underflow	0010000000000000	00800000
positive numbers	0010000000000001	00800001
	to	to
	7FEFFFFFFFFFFFFE	7F7FFFFE
positive overflow	7FEFFFFFFFFFFFFF	7F7FFFFF
$+\infty$	7FF0000000000000	7F800000
NaN$^{1}$	7FF0000000000001	7F800001
	to	to
	7FFFFFFFFFFFFFFF	7FFFFFFF
$-0$	8000000000000000	80000000
negative	8000000000000001	80000001
denormalized	to	to
	800FFFFFFFFFFFFF	807FFFFF
negative underflow	8010000000000000	80800000
negative numbers	8010000000000001	80800001
	to	to
	FFEFFFFFFFFFFFFE	FF7FFFFE
negative overflow	FFEFFFFFFFFFFFFF	FF7FFFFF
$-\infty$	FFF0000000000000	FF800000
NaN$^{1}$	FFF0000000000001	FF800001
	to	to
	FFFFFFFFFFFFFFFF	FFFFFFFF

$^1$ Certain values may be designated as quiet NaN (no diagnostic when used) or signaling (produces diagnostic when used) by particular implementations.