POSITION - position descriptors for the BSORT command.

Position descriptors are used to describe positions within records for key-items like "Before=" and "FRom=". Positions are given with numbers followed by an indication of units. The following units are recognized.

Asciicharacters, BYtes, Characters: equivalent to nine bits. This is the default if no units are specified with a number.
BcdCharacters: equivalent to six bits.
Bits: equivalent to a single bit.
Doublewords: equivalent to two full words (72 bits).
Eisdigits, Nibbles: equivalent to half a byte. Two nibbles/EIS-digits will always equal nine bits. One nibble/EIS-digit is five bits if it begins on a byte boundary, and four bits otherwise.
Words: equivalent to a full word (36 bits).

All positions are indexed from zero. Thus "FRom=10c" indicates that the key begins on the 11th character of the record.

Position descriptors may be concatenated into one long position. Thus

FRom=10w3by2b

indicates that the field begins with the third bit in the fourth byte of the 11th word of the record. When a position consists of more than one position descriptor, each descriptor MUST have a unit specified explicitly. Thus

FRom=10

defaults to "10c" but

FRom=10w3

is invalid.

The position descriptors may also be delimited by spaces, commas, or "+" signs, as in

FRom="10w 3by",Before="11w,2by"
Length=3w+2bits

Negative numbers are allowed in position descriptors, e.g.

Before=10w-1c

However, the final result must be positive when translated into bits. (Note that with +Raw input, you are allowed to back up past position zero into the RCW which normally precedes each record; however, you cannot back up past the start of the RCW.)

In general, keys may begin on any bit boundary; however, if the "Field=" or "Ignore=" item appears in the key-string, the key can only begin on a byte boundary. Furthermore, EIS comparisons may only be made on appropriate 4-bit or 9-bit boundaries.

POSITION - position descriptors for the BSORT command.

See Also: