##################################################
#                                      v2022.06.30
# Converts a decimal number to scientific notation.
#
# This function converts a number to standard scientific notation.
# This function expects to receive a decimal number,
# and it returns a number in scientific notation.
# Both the input and output numbers are treated as strings.
# If the input string had any spaces, commas or any other illegal
# characters, those are removed from the number.
#
# Example:
#
#   Input: ""              Output: "+0E+0"
#   Input: "-20.35"        Output: "-2.035E+1"
#   Input: "0.000333E-12"  Output: "+3.33E-16"
#   Input: "000.00001000"  Output: "+1E-5"
#   Input: "$ 75,800.99 "  Output: "+7.580099E+4"
#   Input: " (12.49) abc"  Output: "-1.249E+1"
#   Input: " 2008300"      Output: "+2.0083E+6"
#   Input: ".225E+76"      Output: "+2.25E+75"
#   Input: "10,000,000,000,000,000,000,000,000,000,000,000,000,000"
#                          Output: "+1E+40"
#
# Usage: STRING = SCI(STRING N)
#
sub SCI
{
  defined $_[0] or return '+0E+0';
  my $NUM = $_[0];

  my $M = '';     # Mantissa will be stored here
  my $E = '';     # Exponent will be stored here
  my $SIGN = 43;  # Is this a negative number? (43=pos 45=neg)
  my $DEC = -1;   # Remember the position of the decimal point
  my $EX = 0;     # Exponent (0=no_exp 1=exp_found 43=pos_exp 45=neg_exp)
  my $Z = -1;     # Start position of the last zero
  my $N = -1;     # Position of the first non-zero digit

  for (my $i = 0; $i < length($NUM); $i++)
  {
    my $c = vec($NUM, $i, 8);
    if ($EX)                   # PROCESS EXPONENT:
    {
      if (($c == 43 || $c == 45) && $EX == 1)
        { $EX = $c; }
      elsif ($c > 47 && $c < 58)
        { $E .= chr($c); }
      elsif (length($E))
        { last; }              # What comes after the exponent? Nothing!
    }
    else                       # PROCESS MANTISSA
    {
      if ($c > 47 && $c < 58)  # Digits 0-9
      {
        if ($c == 48)
        {
          if (length($M)) { $M .= '0'; }     # Keep '0' digit only if there are other digits in front of it
          if ($Z < 0) { $Z = length($M); }   # Remember last insignificant zero
        }
        else
        {
          $M .= chr($c);                     # Save digits other than zero
          if ($N < 0) { $N = length($M); }
          $Z = -1;
        }
      }
      elsif ($c == 68 || $c == 69 || $c == 100 || $c == 101)   # D/d/E/e
      {
        if (length($M)) { $EX = 1; }         # Exponent marker found!
      }
      elsif ($c == 46)
      {
        if ($DEC < 0)
        {
          if (length($M) == 0) { $M = '0'; }
          $DEC = length($M);                 # Decimal point found!
        }
        else { last; }                       # A second decimal point???
      }
      elsif (($c == 45 || $c == 40) && length($M) == 0)
      {
        $SIGN = 45;                          # It's a negative number
      }
    }
  }
    
  if (length($M) == 0) { return '+0E+0'; }

  # Convert Exponent to a number for now
  if ($EX) { $EX = ($EX == 45) ? -$E : $E; }

  # Adjust exponent
  if (length($M) > 1)
  {
    if ($DEC == -1) { $EX = $EX + length($M) - 1; }    # No decimal point
    if ($DEC >= 2) { $EX = $EX + $DEC - 1; }           # Yes decimal point
  }

  # Remove trailing zeros
  if ($Z > 0) { $M = substr($M, 0, $Z - 1); }

  # Add decimal point if possible.
  if ($N > 1)
  {
    if (length($M) > $N)
    {
      $M = substr($M, $N - 1, 1) . '.' . substr($M, $N);
      $EX = $EX - $N + 1;
    }
  }
  else
  {
    if (length($M) > 1) { $M = substr($M, 0, 1) . '.' . substr($M, 1); }
  }
  return chr($SIGN) . $M . 'E' . ($EX < 0 ? '' : '+') . $EX;
}


print SCI('00002999999999999900000006.5544433377777777888888880000001');
exit;

# Outputs:
#
# +2.9999999999999000000065544433377777777888888880000001E+21
#