Type ASSEMBLE
Source Lines : 745
Fixes Applied : 3
Most Recent Version : Tuesday, December 12, 1978
Last Fix ID : [HRC323DS]
Module
DMSSRT (SORT)
Function
TO ARRANGE RECORDS WITHIN A FILE IN A DESCENDING
SEQUENTIAL ORDER.
Attributes
DISK RESIDENT
Operation
FROM THE REQUESTED FIELD DEFINITIONS, SORT SETS UP AN
ORDERED SERIES OF MVC'S AT THE BEGINNING OF THE FREE
AREA, IN WHICH THE 'FROM' FIELD IS INPUT RECORD FIELD
LOCATION, THE LENGTH IS THE LENGTH OF THE FIELD, AND
THE 'TO' LOCATION IS THE START OF THE DISTRIBUTION
BUFFER PLUS THE LENGTH OF ANY FIELDS WHICH HAVE COME
BEFORE. THUS, A PRIMARY FIELD OF LENGTH 5 WOULD BE
MOVED INTO DISTRIBUTION BUFFER LOCATION 0, WHILE THE
SECONDARY FIELD, IF ANY WOULD BE MOVED INTO
DISTRIBUTION BUFFER LOCATION 0 PLUS 5. THUS A SINGLE
CONTIGUOUS SORT ELEMENT IS CREATED WHOSE LENGTH IS
THE TOTAL LENGTH OF ALL THE FIELDS.
RECORDS ARE READ IN ONE AT A TIME INTO CONTIGUOUS
AREAS OF STORAGE. A SORT ELEMENT IS CREATED WHICH IS
THEN PLACED IN ASCENDING ORDER IN A SORT TREE, WHERE
EACH ENTRY HAS THE FOLLOWING FORMAT:
DC AL3(LOW)
DC AL3(HIGH)
DC AL3(BACK)
DC XL1(FLAG)
DC AL2(CNT)
DC AL ELEMENT LENGTH PLUS 2 BYTES FOR ITEM NO.
LOW IS ADDRESS OF NEXT LOWER ENTRY
HIGH IS ADDRESS OF NEXT HIGHER ENTRY
BACK IS BACK POINTER TO PREVIOUS ENTRY
FLAG IS USED IN UNWINDING THE TREE TO MARK A DELETED ELEM
CNT INDICATES NUMBER OF DUPLICATES
WHEN THE TREE HAS BEEN COMPLETED, THE CHAIN IS
SEARCHED FOR THE LOWEST ELEMENT, WHICH IS SIGNIFIED
BY A LOW FIELD OF ALL ZEROS. THE FLAG IS SET TO
'USED'. RDBUF IS CALLED WITH THE ITEMNO WHICH WAS
SAVED IN THE MODE. WRBUF WRITES THE RECORD OUT ON
DISK. THE CHAIN IS THEN UNWOUND UPWARDS, WITH EACH
DELETED ENTRY BEING FLAGGED AND THE CORRESPONDING
RECORD WRITTEN OUT, UNTIL THE ENTIRE TREE IS
EXHAUSTED AND THE SORTED FILE IS WRITTEN. THE INPUT
AND OUTPUT FILES ARE CLOSED, STORAGE IS RELEASED, THE
PAGES RELEASED, AND CONTROL IS PASSED BACK TO THE
CALLER.