6.3 RESERV: allocate new file record

      subroutine reserv(len,ifil,name,irec)

Reserve len words of space for a record name on file ifil. If the record already exists, irec controls the placement of the new data.

${\tt irec}=0$

The existing record is marked as redundant by having its name in the directory changed to $-$name, and the new record is written at end of the file.

${\tt irec}<0$

The existing record is overwritten.

${\tt irec}>0$

An extension record is made.

Although in principle explicit calls to reserv are not necessary, since reserv is called by sreibw where required, it is good practice to use it wherever possible. In particular, in the parallel environment, where file records are simulated by global arrays, it is important to use reserv to instruct the I/O software about the size of global arrays to use and thereby avoid excessive fragmentation or overallocation.