program main
      implicit none
      call input
      call table
      print *, 'The program has completed successfully'
      stop
      end


      subroutine input
      implicit none
      integer IERR
      real X_min,X_max,dx,Y_min,Y_max,dy
      real temp_x, temp_y
      common /arguments/ X_min,X_max,dx,Y_min,Y_max,dy
      open(111,FILE='input.txt', status='old', IOSTAT=IERR, err=404)
      read (111,*) X_min,X_max,dx,Y_min,Y_max,dy  
      close(111)
c Checking input values
      if((dx .LE. 0) .OR. (dy .LE. 0)) then
          write(6,*) 'Input values error:  Wrong x/y step'
          stop
      elseif(X_min .GT. X_max .OR. Y_min .GT. Y_max) then
          write(6,*) 'Input values error: Wrong min/max arguments'
          stop
      endif
      !Checking if step is too low
      !Example: x: 0.01; step: 0.000000001; - error
      temp_x = X_min + dx
      temp_y = Y_min + dy
      if((temp_x .EQ. X_min) .OR. (temp_y .EQ. Y_min)) then
          write(6,*) 'Input values error: x/y step is too low'
          stop
      endif
      return
c Input error        
  404 if(IERR .EQ. 29) then !FOR$IOS_FILNOTFOU
          write(6,*) 'Error: File does not exist'
      elseif(IERR .EQ. 43) then !FOR$IOS_FILNAMSPE
          write(6,*) 'Error: File name specification error'
      elseif(IERR .EQ. 9) then !FOR$IOS_PERACCFIL
          write(6,*) 'Error: Permission to access file denied'
      else
          write(6,*) 'Error: Undefined error, code = ', IERR
      endif
      print *, 'Input file error', IERR
      stop
      end


      subroutine cotg(value,eps_null,result,error_code,error_str)
      implicit none
      real result,value,temp_sin,temp_cos,eps_null
      integer error_code
      character*3 error_str
      error_code = 0
      error_str = ' '
      temp_sin = sin(value)
      if(temp_sin .EQ. 0) then
          error_code = 1 !divided by zero
          error_str = 'NaN'
          return
      elseif(abs(temp_sin) .LE. eps_null) then
          error_code = -1 !infinity
          error_str = 'INF'
          return
      endif
      temp_cos = cos(value)
      if(abs(temp_cos) .LE. eps_null) then
        temp_cos = 0
      endif
      result = temp_cos/temp_sin
      end

      subroutine find_steps(array,min,max,dx,n,eps,eps_null)
      implicit none
      character*15 str1,str2,str3
      integer i,n
      real array(*),eps,temp,min,max,dx,eps_null
      real epsilon_power, power_temp
      n = 5
      temp = min
      do 10 i=1,n
          !Check max, eps = 10**(-3 + [lg|dx|])
          if(temp .GE. max .OR. abs(temp-max) .LE. eps) then
              n = i
              array(n) = max
              return
          endif
          !End check max
          if(abs(temp) .LE. eps_null) temp = 0
          array(i) = temp
          !Skip invisible steps
          write (str3,'(E13.7)') temp
          write (str1,'(A6)') str3
          write (str2,'(A6)') str3
   20     if(str1 .EQ. str2) then
              temp = temp + dx
              write (str3,'(E13.7)') temp
              write (str1,'(A6)') str3
              goto 20
          endif
          !End skip invisible steps
          power_temp = epsilon_power(temp,dx,eps)
          temp = anint(temp*10**(-power_temp))*10**power_temp
          if(abs(temp) .LE. eps_null) temp = 0
   10 continue
      min = temp
      return
      end

      real function epsilon_power(a,da,epsilon_da)
      implicit none
      real a, da, epsilon_da
      if(abs(a) .LT. 1) then
          if(abs(a) .GT. epsilon_da) then
              epsilon_power = aint(log10(abs(a))) - 4
          else
              epsilon_power = aint(log10(abs(a-da))) - 4
          endif
      else
          epsilon_power = aint(log10(abs(a))) - 3
      endif
      end

      
      subroutine table
      implicit none
      integer IERR,error_code,n,m,i,j
      real array_x(5), array_y(5)
      character*3 error_string
      real X_min,X_max,dx,Y_min,Y_max,dY,degreeToRadian,result
      real eps_dx, eps_dy, temp, eps_null
      common /arguments/ X_min,X_max,dx,Y_min,Y_max,dY
      common /const/ degreeToRadian
      degreeToRadian=3.1415926/180
      open(112,FILE='output.txt',status='unknown',IOSTAT=IERR,err=404)
      eps_null = 1e-10
      eps_dx = 10**aint(log10(abs(dx)) - 3)
      eps_dy = 10**aint(log10(abs(dy)) - 3)
      if(eps_null .GE. eps_dx) then
          eps_null = eps_dx*degreeToRadian
      elseif(eps_null .GE. eps_dy) then
          eps_null = eps_dy*degreeToRadian
      endif
   10 continue
          call find_steps(array_x,X_min,X_max,dx,n,eps_dx,eps_null)
          temp = Y_min
   20     continue
              m = 5
              call find_steps(array_y,temp,Y_max,dy,m,eps_dy,eps_null)
              do i = 1, n + 1
                  write(112,1000) !print ---
              enddo
              write(112,1020)
              write(112,1030) 'y/x'
              write(112,1010) (array_x(i), i=1,n)
              write(112,1020)
              do i = 1, n + 1
                  write(112,1000) !print ---
              enddo
              write(112,1020)
              do 100 i = 1,m
                  write(112,1010) array_y(i)
                  do 110 j = 1,n
                    call cotg((array_y(i)+array_x(j))*degreeToRadian, 
     *              eps_null,result, error_code, error_string)
                    if(error_code .EQ. 0) then
                        write(112,1010) result
                    else
                        write(112,1030) error_string
                    endif
  110             continue
                  write(112,1020)
  100         continue
              do i = 1, n + 1
                  write(112,1000) !print ---
              enddo
              write(112,1020)
          if(array_y(m) .NE. Y_max) goto 20 !end do while
      if(array_x(n) .NE. X_max) goto 10 !end do while
      close(112)
      return
c Formats
 1000 format(15('-')\)
 1010 format('| 'E11.4\' |')
 1020 format(/\)
 1030 format('|     'A\'     |')
c Output file errors
  404 if(IERR .EQ. 43) then !FOR$IOS_FILNAMSPE
          write(6,*) 'Output error: File specification error'
      elseif(IERR .EQ. 10) then !FOR$IOS_CANOVEEXI
          write(6,*) 'Output error: Cannot overwrite existing file'
      elseif(IERR .EQ. 21) then !FOR$IOS_DUPFILSPE
          write(6,*) 'Output error: Duplicate file specifications'
      else
          write(6,*) 'Output error: Undefined error, code = ', IERR
      endif
      print *, 'Output file error ', IERR
      stop
      end