Absence validation formula is calculating absence wrong. Mismatch between UI and Formula

Summary:

Absence validation formula is calculating absence wrongly may be due to function that is used. Not sure which function or DBI can be used. Mismatch between UI and Formula

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Code Snippet (add any code snippets that support your topic, if applicable):

/* ****************************************************************************
DBI Default Section
******************************************************************************/

DEFAULT FOR PER_ASG_PERSON_NUMBER IS '000000'
/===================================== INPUTS SECTION BEGIN======================================/

INPUTS ARE IV_END_DATE (date), IV_START_DATE (date), IV_TOTALDURATION (number)

VALID = 'Y'
ERROR_CODE=' '
ERROR_MESSAGE = ' '

ln_assignment_id = GET_CONTEXT(HR_ASSIGNMENT_ID,-1)