As provided.  NOTE: Numerous "Use of uninitialized value in..." lines 28, 32, 54, 57
25 trials of GMDT (471.000ms total), 18.840ms/trial

Editing lines 27,28, 29 giving
		$szIntegerPart = ($2||'');
		$szDecimalPart = ($4||'') . ($6||'');
		$szFloatPart  = $7||'';
25 trials of GMDT (250.000ms total), 10.000ms/trial

Converted if (condition) { return 'constant'; }	to		return 'constant' if condition;
25 trials of GMDT (200.000ms total), 8.000ms/trial

Changed 		if (not defined $varValue) { return 'NULL' }		to			return 'NULL' unless $varValue;
25 trials of GMDT (151ms total), 6.040ms/trial

Chnaged
	$iLength = length $varValue;
	return( 'CHAR(' . $iLength . ')' );
to
	return 'CHAR(' . length($varValue) . ')';
and removed redundant variable;
25 trials of GMDT (100.000ms total), 4ms/trial

Changed
	my $varValue = shift(@_)];
	my ($iScale, $iPrecision
	my ($szIntegerPart, $szDecimalPart, $szFloatPart);
to
	my $varValue = $_[0];
	my ($iScale, $iPrecision, $szIntegerPart, $szDecimalPart, $szFloatPart);
25 trials of GMDT (121.000ms total), 4.840ms/trial	
	
Changed constant numeric expressions to constant subs.

use constant SHORT_MIN	=> -32768;
use constant SHORT_MAX	=>  32767;
use constant LONG_MIN	=> -2147483648;
use constant LONG_MAX	=>  2147483647;
use constant FLOAT_MIN	=> 1.175 * 10 **  -38;
use constant FLOAT_MAX	=> 3.402 * 10 **   38;
use constant DOUBLE_MIN => 1.175 * 10 ** -308;
use constant DOUBLE_MAX => 3.402 * 10 **  308;

25 trials of GMDT (90ms total), 3.600ms/trial

Changed 
	#                         1 2     3  4         5  6        7
	if ($varValue =~ /^ [+-]? ( (\d+) (\.(\d*))? | (\.(\d+)) ) ([Ee][+-]?\d+)? $/ox ) {
		$szIntegerPart	= ($2||'');
		$szDecimalPart	= ($4||'') . ($6||'');
		$szFloatPart	= ($7||'');
to 
	if ($varValue =~ /^ [+-]? (?: (\d+) (?:\.(\d*))? | (?:\.(\d+)) ) ([Ee][+-]?\d+)? $/ox ) {
		#Check for numeric types
		$szIntegerPart	= ($1||'');
		$szDecimalPart	= ($2||'') . ($3||'');
		$szFloatPart	= ($4||'');

No discernable difference over 25 trials - increased number of trials from 25 to 500
500 trials of GMDT (1.455s total), 2.910ms/trial

Moved return from string to top of sub, 

	return 'CHAR(' . length($varValue) . ')'
		unless $varValue =~ /^ [+-]? (?: (\d+) (?:\.(\d*))? | (?:\.(\d+)) ) ([Ee][+-]?\d+)? $/ox ;
		
500 trials of GMDT (1.201s total), 2.402ms/trial

Made the regex a constant sub. Difference to small to be sure of any advantage one way or the other.

use constant RE_NUMERIC	=> qr/^ [+-]? (?: (\d+) (?:\.(\d*))? | (?:\.(\d+)) ) ([Ee][+-]?\d+)? $/x;
...
		unless $varValue =~ RE_NUMERIC;


500 trials of GMDT (1.111s total), 2.222ms/trial