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SECTION 7. STANDARD EXTENSIONS

following shall be in order of decreasing significance, ending with the least significant

bit. A bit array shall be composed of an integral number of bytes, with those bits

following the end of the data set to zero. No null value is defined for bit arrays.

Character If the value of the TFORMn keyword specifies data type A, field n shall

contain a character string of zero or more members, composed of the restricted set

of ASCII text characters. This character string may be terminated before the length

specified by the repeat count by an ASCII NULL (hexadecimal code 00). Characters

after the first ASCII NULL are not defined. A string with the number of characters

specified by the repeat count is not NULL terminated. Null strings are defined by the

presence of an ASCII NULL as the first character.

Unsigned 8-Bit Integer If the value of the TFORMn keyword specifies data type B,

the data in field n shall consist of unsigned 8-bit integers, with the most significant bit

first, and subsequent bits in order of decreasing significance. Null values are given by

the value of the associated TNULLn keyword. Signed integers can be represented using

the convention described in § 5.2.5.

16-Bit Integer  If the value of the TFORMn keyword specifies data type I, the data in

field n shall consist of two's complement signed 16-bit integers, contained in two bytes.

The most significant byte shall be first (big endian byte order). Within each byte the

most significant bit shall be first, and subsequent bits shall be in order of decreasing

significance. Null values are given by the value of the associated TNULLn keyword.

Unsigned integers can be represented using the convention described in § 5.2.5.

32-Bit Integer If the value of the TFORMn keyword specifies data type J, the data

in field n shall consist of two's complement signed 32-bit integers, contained in four

bytes. The most significant byte shall be first, and subsequent bytes shall be in order of

decreasing significance (big endian byte order). Within each byte, the most significant

bit shall be first, and subsequent bits shall be in order of decreasing significance. Null

values are given by the value of the associated TNULLn keyword. Unsigned integers can

be represented using the convention described in § 5.2.5.

64-Bit Integer If the value of the TFORMn keyword specifies data type K, the data

in field n shall consist of two's complement signed 64-bit integers, contained in eight

bytes. The most significant byte shall be first, and subsequent bytes shall be in order

of decreasing significance. Within each byte, the most significant bit shall be first, and

subsequent bits shall be in order of decreasing significance (big endian byte order). Null

values are given by the value of the associated TNULLn keyword. Unsigned integers can

be represented using the convention described in § 5.2.5.

FITS Standard