/******************************************************************

                  SUBROUTINE LOOPREAD

 LOOPREAD READS IN THE STARTING AND ENDING PROFILE NUMBERS FOR
 A SPECIFIC YEAR AND MONTH (OR JUST FOR A YEAR).  THE VALUES ARE
 CONTAINED IN A .L FILE IN A TWO INTEGER STRUCTURE

********************************************************************/

/*******************************************************************

 DEFINE LOOP AS A WRITE2 (TWO INTEGER) STRUCTURE TO READ IN THE
 STARTING AND ENDING LOOP VALUES.

********************************************************************/

struct write2 loop;

loopread_(  

 int *jstart,              /* STARTING PROFILE NUMBER FOR YEAR
                              (AND MONTH) */

 int *jend,                /* ENDING PROFILE NUMBER FOR YEAR
                              (AND MONTH) */

 int *fn,                  /* FILE IDENTIFICATION NUMBER FOR FILE
                              WITH LOOP INFORMATION */

 int *iyear,               /* REQUESTED YEAR */

 int *month,               /* REQUESTED MONTH (13 IS ALL MONTHS) */

 int *leof                 /* SET TO ONE IF END OF FILE HAS BEEN 
                              REACHED */

          )


{

/**********************************************************

 PARAMETERS:

  YEAR - INPUT YEAR MINUS 1800, USED TO FIND PROPER POSITION
         IN FILE
  PSIZE - PROPER POSITION IN FILE.  THIS IS FOURTEEN TIMES THE
          CALCULATED YEAR ( ONE FOR EACH MONTH, ONE FOR NO MONTH (0),
          AND ONE FOR ALL MONTHS (13)) PLUS DESIRED MONTH

************************************************************/

 int year = *iyear - 1800;
 int psize;

 
/*************************************************

 ALL YEARS PRIOR TO 1801 ARE PLACED TOGETHER

***************************************************/

 if ( year < 0 ) year = 0;

/**************************************************

 CALCULATE PROPER POSITION OF DESIRED INFORMATION

***************************************************/

 psize = year * 14 + *month;

/***************************************************

 MOVE TO PROPER POSITION IN FILE (FSEEK)
 READ STRUCTURE CONTAINING BEGINNING AND ENDING PROFILE VALUES
 FOR DESIRED YEAR (AND MONTH)

****************************************************/

 fseek( fp[*fn], psize * sizeof( struct write2 ), SEEK_SET );
 fread( &loop, sizeof( struct write2 ), 1, fp[*fn] );

/***************************************************

 IF DESIRED DATE IS PAST END OF FILE, SET *LEOF TO ONE
 AND EXIT SUBROUTINE.

*****************************************************/

 if ( feof( fp[*fn] ) ) {

  *leof = 1;
  return;

 }

/*****************************************************

 SET STARTING VALUE AND ENDING VALUE TO BE SENT TO
 MAIN PROGRAM.

******************************************************/

 *jstart = loop.num;
 *jend = loop.rec;

}