.TITLE RDLEN
	.IDENT /850321/
;+
;.ENTRY RDLEN
; - R D L E N
; FILE:      RDLEN.MAR 
; SYSTEM:     VMS V4.0
; LANGUAGE:   MACRO32
; AUTHOR:     M. OOTHOUDT
; DATE:       850321
;-
;
; ******************************************************************
; * Copyright, 1984, The Regents of the University of California.  *
; *                                                                *
; * This software was produced under a U.S. Government contract    *
; * (W-7405-ENG-36) by the Los Alamos National Laboratory, which   *
; * is operated by the University of California for the U.S. De-   *
; * partment of Energy.  The U.S. Government is licensed to use,   *
; * reproduce, and distribute this software.  Permission is grant- * 
; * ed to the public to copy and use this software without charge, *
; * provided that this notice and any statement of authorship are  *
; * reproduced on all copies.  Neither the Government nor the Uni- *
; * versity makes any warranty, express of implied, or assumes any *
; * liability or responsibility for the use of this software.      *
; ******************************************************************
;
; REFERENCES: 
;
; REVISIONS:  
;+
;
;****PURPOSE: Tell User the number of bytes of user data returned
;		by a FORTRAN Unformatted READ on a LUN.
;
;****RESTRICTIONS:  
;
;****CALLING SEQUENCE:  CALL RDLEN (LUN,LEN)
;
;
;    INPUT:  
;
; LUN = (I*2) LUN READ was done on
; 
;    MODIFIED: None
;
;
;    OUTPUT:  
;
; LEN = (I*2) # of bytes returned to the user by the last READ on LUN
;
;    CMN BLOCKS USED:  None
;
;****RESOURCES:
;	LIBRARIES:   VMSRTL:FOR$RAB
;	OTHER SUBR:  None
;	DISK FILES:  File open on LUN
;	DEVICES:     Device on LUN
;	SGAS:        None
;	EVENT FLAGS: None
;	SYSTEM DIR:  None
;
;****NOTES:  
;	1.  When doing an Unformatted FORTRAN READ on a file, there is
; no way to determine how many bytes were put into the user's array by
; the READ.  This routine will give the correct number of bytes:
;
;	BYTE ARRAY(100)
;	open file on LUN Unformatted
;	READ(LUN)ARRAY
;	CALL RDLEN (LUN,LEN)
;
; LEN contains the number of bytes in ARRAY.
;
;	2.  Unformatted FORTRAN READs and WRITEs can be more than a
; factor of 10 faster (WALL clock and CPU time) than a similar Formatted
; IO.  Thus Unformatted IO should be used wherever possible.  The only
; real reason for using Formatted IO is that a human being will have
; to read the IO.
;
;	3.  Text files created with FORTRAN WRITEs or an EDITOR may be
; READ Unformatted.  However, the OPEN statement for the READ MUST
; specify RECORDTYPE='VARIABLE' to avoid "Segemented record format"
; errors.
;
;	4.  Reads into FORTRAN arrays that are longer than the disk
; record will return an error of 67, "data underrun."  This can usually
; be treated as success.
;-

;	Data
 
	.PSECT QLIB_DATA,WRT,NOEXE
FORRABCALL:			;Arg list for FOR$RAB call
	.LONG 1	
LUN:	.BLKL 1			;Addr of LUN
 

;	Code
 
	.PSECT QLIB_CODE,NOWRT,EXE
 
	.ENTRY RDLEN,^M<>
 
	MOVAL @4(AP),LUN		;Set up FOR$RAB call
	CALLG FORRABCALL,G^FOR$RAB	;RAB addr put into R0
 
	MOVW RAB$W_RSZ(R0),@8(AP)	;Return rec size
 
	RET
	.END