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

                   SUBROUTINE SEQREAD

 SEQREAD READS ALL SEQUENTIAL MASKS TO FIND THE NEXT PROFILE
 TO BE EXAMINED.  A SEQUENTIAL MASK IS A MASK WHICH CONTAINS
 ONLY PROFILE NUMBERS.  THERE ARE TWO TYPES OF SEQUENTIAL MASKS;
 THE FIRST IS INCLUSIVE MASKS.  INCLUSIVE MASKS CONTAIN THE PROFILE
 NUMBERS OF THOSE PROFILES WHICH ARE TO BE EXAMINED IN THE MAIN
 PROGRAM.  THE SECOND TYPE IS EXCLUSIVE MASKS.  THESE MASKS CONTAIN
 NUMBERS OF PROFILES WHICH ARE EXPRESSLY NOT TO BE EXAMINED IN THE
 MAIN PROGRAM.  SEQREAD READS EACH MASK UNTIL THE NEXT PROFILE NUMBER
 WHICH IS IN AN INCLUSIVE MASK AND NOT IN AN EXCLUSIVE MASK IS FOUND.
 THE PRESENT PROFILE NUMBER FOR EACH MASK IS STORED IN JPRESENT.

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

seqread_(

 int *jj,           /* PRESENT PROFILE RECORD NUMBER */

 int *nmask,        /* TOTAL NUMBER OF SEQUENTIAL MASKS */

 int *nmask1,       /* NUMBER OF INCLUSION MASKS */

 int *eof,          /* END OF SEARCH MARKER. SET TO ONE WHEN
                       ALL FILES HAVE REACHED THEIR END OF FILE */

 int *allend,       /* NUMBER OF FILES WHICH HAVE REACHED THEIR
                       END OF FILE */

 int *fn            /* FILE IDENTIFICATION NUMBERS FOR EACH MASK FILE */

         )

{

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

 I - COUNTER
 FOUND - DENOTES WHETHER A PROFILE RECORD NUMBER HAS BEEN FOUND
 JJIN - PROFILE RECORD NUMBER WHICH IS RETURNED TO THE MAIN
        PROGRAM.  IT IS INITIALLY SET TO A VERY LARGE NUMBER
        SINCE THE SMALLEST OF ALL PROFILE RECORD NUMBERS CULLED
        FROM THE VARIOUS MASKS IS THE PROFILE RECORD NUMBER
        RETURNED.  HENCE JJIN MUST FIRST BE SET TO A NUMBER
        WHICH IS LARGER THAN ANY PROFILE RECORD NUMBER.

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

 int i;
 int found = 0;
 int jjin = 300000000;

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

 IF THERE ARE NO INCLUSIVE MASKS, SET THE OUTPUT RECORD NUMBER
 TO THE PRESENT RECORD NUMBER.  IN THIS WAY, THE PRESENT RECORD
 NUMBER (PLUS ONE) WILL BE CHECKED AGAINST EXCLUSIVE MASKS.

 IF ALL MASKS ARE INCLUSIVE, SET FOUND TO -1.  THIS IS THE ONLY
 WAY TO CHECK THE NEXT VALUE IN INCLUSIVE MASKS, SINCE MASKS
 ARE ONLY CHECKED IF FOUND IS LESS THAN THE NUMBER OF EXCLUSIVE
 MASKS. 

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

 if ( *nmask1 == 0 ) jjin = *jj;
 if ( *nmask - *nmask1 == 0 ) found = -1;


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

 IF FOUND IS LESS THAN THE NUMBER OF EXCLUSIVE MASKS, CHECK EACH
 MASK FILE.

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

 while ( found < ( *nmask - *nmask1 )  ) {

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

 IF THERE ARE NO INCLUSIVE MASKS, CHECK THE NEXT SUCCESSIVE
 PROFILE AGAINST THE EXCLUSIVE MASKS.

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

  if ( *nmask1 == 0 ) jjin += 1;

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

 IF THERE ARE NO EXCLUSIVE MASKS, SET FOUND TO ONE, SINCE THE
 NEXT VALUE READ FROM THE INCLUSIVE MASKS IS AUTOMATICALLY THE
 OUTPUT VALUE.  OTHERWISE RESET FOUND.

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

  if ( *nmask - *nmask1 == 0 ) found = 1;
  else found = 0;

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

 CHECK EACH INCLUSIVE MASK.

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

  for ( i = 0; i < *nmask1; i++ ) {

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

 IF A MASK HAS ALREADY REACHED THE END OF ITS FILE, SUBTRACT ONE
 FROM *ALLEND, SINCE ONE WILL AGAIN BE ADDED AFTER AN ATTEMPT
 TO READ THE FILE.

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

   if (feof(fp[*(fn+i)])) *allend -=1;

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

 WHILE THE PRESENT PROFILE RECORD NUMBER IN THE MASK IS LESS OR
 EQUAL TO THE LAST INVESTIGATED PROFILE RECORD NUMBER, READ THE
 NEXT PROFILE RECORD NUMBER FROM FILE (UNLESS THE FILE HAS BEEN
 COMPLETELY READ IN.

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

   while ( jpresent[ i ] <= *jj && !feof( fp[ *(fn + i) ] )) {

    fread( &jpresent[i], sizeof( int ) , 1, fp[*(fn+i)]);

   }

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

 IF THE END OF FILE HAS BEEN REACHED, ADD ONE TO THE END OF FILE
 COUNTER.
****************************************************************/

   if (feof(fp[*(fn+i)])) *allend +=1;

  }

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

 IF NOT ALL FILES HAVE REACHED THEIR END OF FILE, FIND THE 
 LOWEST PROFILE NUMBER FROM ALL THE MASKS AND SET THIS AS THE
 NEXT PROFILE TO BE INVESTIGATED.

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

  if ( *allend < *nmask1 ) {

   jjin = 300000000;

   for ( i = 0; i < *nmask1; i++ ) {

    if ( !feof(fp[*(fn+i)]) && jpresent[i] < jjin )
    jjin = jpresent[i];

   }

  }

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

 IF ALL MASK FILES HAVE BEEN COMPLETELY READ, SET EOF TO ONE
 TO ALERT THE MAIN PROGRAM.

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

  else if ( *nmask1 > 0 ) {

   *eof = 1;
   return;

  }

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

 SET THE PROFILE RECORD NUMBER TO BE INVESTIGATED AS THE
 PRESENT PROFILE.

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

  *jj = jjin;

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

 READ IN THE NEXT PROFILE RECORD NUMBERS FROM THE EXCLUSIVE
 MASKS.

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

  for ( i = *nmask1; i < *nmask; i++ ) {

   while ( jpresent[ i ] < jjin && !feof( fp[ *(fn + i) ] )) {

    fread( &jpresent[i], sizeof( int ) , 1, fp[*(fn+i)]);

   }

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

  IF THE VALUE IN THE EXCLUSIVE MASK IS NOT EQUAL TO THE PRESENT
  PROFILE NUMBER OR THE EXCLUSIVE MASK HAS BEEN COMPLETELY READ,
  ADD ONE TO FOUND.  WHEN FOUND EQUALS THE NUMBER OF EXCLUSIVE
  MASKS, THE PRESENT PROFILE RECORD NUMBER IS OUTPUT TO THE
  MAIN PROGRAM AS THE NEXT PROFILE TO BE INVESTIGATED.

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

   if ( feof(fp[*(fn+i)]) || jpresent[i] != jjin ) found +=1;

  }

 }

}