Can anyone explain what this code does.

Question

<b>Below is the FM for a  SAP Exit Variable ( 0FPER - Fiscal Period Variable ) , I would really appreciate if someone can give some explanation what does the code do.</b>
FUNCTION RSVAREXIT_0F_FPER.
""Lokale Schnittstelle:
*"       IMPORTING
*"             VALUE(I_VNAM) LIKE  RSZGLOBV-VNAM
*"             VALUE(I_VARTYP) LIKE  RSZGLOBV-VARTYP
*"             VALUE(I_IOBJNM) LIKE  RSZGLOBV-IOBJNM
*"             VALUE(I_S_COB_PRO) TYPE  RSD_S_COB_PRO
*"             VALUE(I_S_RKB1D) TYPE  RSR_S_RKB1D
*"             VALUE(I_S_RKB1F) TYPE  RRO01_S_RKB1F
*"             VALUE(I_THX_VAR) TYPE  RRO01_THX_VAR
*"       EXPORTING
*"             VALUE(E_T_RANGE) TYPE  RSR_T_RANGESID
*"       EXCEPTIONS
*"              UNKNOWN_VARIABLE
*"              UNEXPECTED_VARTYPE
*"              INVALID_PERIV
*"              VARIABLE_INITIAL
*"              NO_REPLACEMENT
  data:
  l_s_range   type rs_s_range,
  ld_periv    type rro01_s_rkb1f-periv,
  ld_curdate  like sy-datum,
  ld_poper    like t009b-poper,
  ld_fiscyear like t009b-bdatj.
  refresh e_t_range.
  clear l_s_range.
  l_s_range-sign = 'I'.
  l_s_range-opt  = 'BT'.
  case i_vartyp.
    when rro04_c_vartyp-formula.
*--- Determine fiscal year variant
      call function 'BWCO_FISCVARNT_GET'
           exporting
                i_s_rkb1d        = i_s_rkb1d
                i_s_rkb1f        = i_s_rkb1f
                i_thx_var        = i_thx_var
           importing
                e_periv          = ld_periv
           exceptions
                no_replacement   = 1
                unknown_variable = 2
                others           = 3.
      case sy-subrc.
        when 0.
        when 2.
          raise unknown_variable.
        when others.
          raise no_replacement.
      endcase.
      if ld_periv is initial.
        raise invalid_periv.
      endif.
*--- Determine current fiscal year
      ld_curdate = sy-datum.
      call function 'DATE_TO_PERIOD_CONVERT'
           exporting
                i_date         = ld_curdate
                i_periv        = ld_periv
           importing
                e_buper        = ld_poper
                e_gjahr        = ld_fiscyear
           exceptions
                input_false    = 1
                t009_notfound  = 2
                t009b_notfound = 3
                others         = 4.
      if not sy-subrc is initial.
        raise invalid_periv.
      endif.
*--- Determine the highest fiscal period in the current fiscal year
      CALL FUNCTION 'GET_ACCOUNT_OF_PERIODS'
           EXPORTING
                I_GJAHR         = ld_fiscyear
                I_PERIV         = ld_periv
           IMPORTING
                E_ANZBUPER      = ld_poper
           EXCEPTIONS
                INPUT_FALSE     = 1
                T009B_NOTFOUND  = 2
                T009_NOTFOUND   = 3
                OTHERS          = 4
      IF SY-SUBRC <> 0.
            raise invalid_periv.
      ENDIF.
*--- fill value ranges
      l_s_range-low = ld_poper.
      append l_s_range to e_t_range.
    when others.
      raise unexpected_vartype.
  endcase.
endfunction.

Answer 1

1) Fiscal year variant is determined using Function Module - 'BWCO_FISCVARNT_GET'
2) With Fiscal variant & Current Date as input to Function Module - 'DATE_TO_PERIOD_CONVERT' gets Fiscal Year.
3) With Fiscal year & variant as input to 'GET_ACCOUNT_OF_PERIODS' gets 
the highest fiscal period in the current fiscal year