Appendix B

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 B1: IEEE Floating Point Formats

IEEE value	Double Precision	Single Precision
+0	0000000000000000	00000000
denormalized	0000000000000001 to 000FFFFFFFFFFFFF	00000001 to 007FFFFF
positive underflow	0010000000000000	00800000
positive numbers	0010000000000001 to 7FEFFFFFFFFFFFFE	00800001 to 7F7FFFFE
positive overflow	7FEFFFFFFFFFFFFF	7F7FFFFF
$+\infty$	7FF0000000000000	7F800000
NaN1/TD>	7FF0000000000001 to 7FFFFFFFFFFFFFFF	7F800001 to 7FFFFFFF
-0	8000000000000000	80000000
negative denormalized	8000000000000001 to 800FFFFFFFFFFFFF	80000001 to 807FFFFF
negative underflow	8010000000000000	80800000
negative numbers	8010000000000001 to FFEFFFFFFFFFFFFE	80800001 to FF7FFFFE
negative overflow	FFEFFFFFFFFFFFFF	FF7FFFFF
$-\infty$	FFF0000000000000	FF800000
NaN1	FFF0000000000001 to FFFFFFFFFFFFFFFF	FF800001 to FFFFFFFF

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