Update ascii - second round: clean up the code and implement robust versions of to_lower and to_upper

src/stdlib_ascii.f90

@@ -60,6 +60,9 @@ module stdlib_ascii
  character(len=*), public, parameter :: lowercase = letters(27:) !! a .. z
  character(len=*), public, parameter :: whitespace = " "//TAB//VT//CR//LF//FF !! ASCII _whitespace
 
+ character(len=26), parameter, private :: lower_case = 'abcdefghijklmnopqrstuvwxyz'
+ character(len=26), parameter, private :: upper_case = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
+
 contains
 
  !> Checks whether `c` is an ASCII letter (A .. Z, a .. z).
@@ -135,7 +138,9 @@ pure logical function is_punctuation(c)
  pure logical function is_graphical(c)
  character(len=1), intent(in) :: c !! The character to test.
  integer :: ic
- ic = iachar(c) ! '!' '~'
+ ic = iachar(c)
+ !The character is graphical if it's between '!' and '~' in the ASCII table,
+ !that is: printable but not a space
  is_graphical = (int(z'21') <= ic) .and. (ic <= int(z'7E'))
  end function
 
@@ -144,22 +149,25 @@ pure logical function is_graphical(c)
  pure logical function is_printable(c)
  character(len=1), intent(in) :: c !! The character to test.
  integer :: ic
- ic = iachar(c) ! '~'
- is_printable = c >= ' ' .and. ic <= int(z'7E')
+ ic = iachar(c)
+ !The character is printable if it's between ' ' and '~' in the ASCII table
+ is_printable = ic >= iachar(' ') .and. ic <= int(z'7E')
  end function
 
  !> Checks whether `c` is a lowercase ASCII letter (a .. z).
  pure logical function is_lower(c)
  character(len=1), intent(in) :: c !! The character to test.
- is_lower = (c >= 'a') .and. (c <= 'z')
+ integer :: ic
+ ic = iachar(c)
+ is_lower = ic >= iachar('a') .and. ic <= iachar('z')
  end function
 
  !> Checks whether `c` is an uppercase ASCII letter (A .. Z).
  pure logical function is_upper(c)
  character(len=1), intent(in) :: c !! The character to test.
  integer :: ic
  ic = iachar(c)
- is_upper = (ic >= iachar('A')) .and. (ic <= iachar('Z'))
+ is_upper = ic >= iachar('A') .and. ic <= iachar('Z')
  end function
 
  !> Checks whether or not `c` is a whitespace character. That includes the
@@ -169,7 +177,7 @@ pure logical function is_white(c)
  character(len=1), intent(in) :: c !! The character to test.
  integer :: ic
  ic = iachar(c) ! TAB, LF, VT, FF, CR
- is_white = (ic == iachar(' ')) .or. (ic >= int(z'09') .and. ic <= int(z'0D'));
+ is_white = ic == iachar(' ') .or. (ic >= int(z'09') .and. ic <= int(z'0D'))
  end function
 
  !> Checks whether or not `c` is a blank character. That includes the
@@ -178,31 +186,39 @@ pure logical function is_blank(c)
  character(len=1), intent(in) :: c !! The character to test.
  integer :: ic
  ic = iachar(c) ! TAB
- is_blank = (ic == iachar(' ')) .or. (ic == int(z'09'));
+ is_blank = ic == iachar(' ') .or. ic == int(z'09')
  end function
 
  !> Returns the corresponding lowercase letter, if `c` is an uppercase
  ! ASCII character, otherwise `c` itself.
  pure function to_lower(c) result(t)
  character(len=1), intent(in) :: c !! A character.
- character(len=1) :: t
- integer :: diff
- diff = iachar('A')-iachar('a')
- t = c
- ! if uppercase, make lowercase
- if (is_upper(t)) t = achar(iachar(t) - diff)
+ character(len=1) :: t
+ integer :: k
+
+ k = index( upper_case, c )
+
+ if ( k > 0 ) then
+ t = lower_case(k:k)
+ else
+ t = c
+ endif
  end function
 
  !> Returns the corresponding uppercase letter, if `c` is a lowercase
  ! ASCII character, otherwise `c` itself.
  pure function to_upper(c) result(t)
  character(len=1), intent(in) :: c !! A character.
- character(len=1) :: t
- integer :: diff
- diff = iachar('A')-iachar('a')
- t = c
- ! if lowercase, make uppercase
- if (is_lower(t)) t = achar(iachar(t) + diff)
+ character(len=1) :: t
+ integer :: k
+
+ k = index( lower_case, c )
+
+ if ( k > 0 ) then
+ t = upper_case(k:k)
+ else
+ t = c
+ endif
  end function
 
 end module