#!/usr/bin/perl -wl

use strict;

#######################
## string numerifier ##
#######################

# SI prefix to exponent value conversion table
my %SI = (
             Y => +24, # yotta
             Z => +21, # zetta
             E => +18, # exa
             P => +15, # peta
             T => +12, # terra
             G => +9,  # giga
             M => +6,  # mega
             k => +3,  # kilo
             K => +3,  # kilo
             "" => 0,  # default is no SI prefix
             m => -3,  # milli
             u => -6,  # micro
             n => -9,  # nano
             p => -12, # pico
             f => -15, # femto
             a => -18, # atto
             z => -21, # zepto
             y => -24, # yocto
         );

sub num
{
    my ($numstr) = @_;

    # string must contain digit
    if ($numstr =~ /\d/)
    {
        # clean string for best chance at numerification
        my ($sign, $exponent, $siprefix) = ("+", 0, "");
        if ($numstr =~ /^[^.]*\d/) # does first digit appear before po
+tential decimal point?
        {
            $numstr =~ s/^.*?([+-]?)(\d+[.]?\d*)(?:[eE]([+-]?\d+))?([Y
+ZEPTGMkKmunpfazy])?.*/$2/;
            $sign     = $1 if $1;
            $exponent = $3 if $3;
            $siprefix = $4 if $4;
        }
        else
        {
            $numstr =~ s/^.*?([+-]?)(\d*[.]?\d+)(?:[eE]([+-]?\d+))?([Y
+ZEPTGMkKmunpfazy])?.*/$2/;
            $sign     = $1 if $1;
            $exponent = $3 if $3;
            $siprefix = $4 if $4;
        }

        # convert SI prefixes -- example: ".16E2m" => ".16e-1" => 0.01
+6
        if ($exponent || $siprefix)
        {
            $exponent += $SI{$siprefix};
            $numstr   .= "e".$exponent;
        }

        # numerify string according to nearest sign
        {
            no warnings 'numeric';
            $numstr = -+-$numstr;                 # high-precedence nu
+merifier
            $numstr =   -$numstr if $sign eq "-"; # negative if last s
+ign is "-"
        }
    }
    else
    {
        $numstr = undef;
    }

    return($numstr);
}

##############
# test cases #
##############

print "|".num("+-- 123.mA")."|";          # output: "|0.123|"
print "|".num(" -+--.15e4u99..99.0")."|"; # output: "|-0.0015|"
print "|".num(" -+-- 789. G5e2")."|";     # output: "|789|"

print "|".(1e-6 == num("1e-6"))."|"; # output: "|1|"
print "|".(1e-6 == num("1e3n"))."|"; # output: "|1|"
print "|".(1e-6)."|".(1e3*1e-9)."|"; # output: "|1e-06|1e-06|"
print "|".(1e-6 == 1e3*1e-9)."|";    # output: "||"  -- low-level FP l
+imitation, perhaps with C's strtod()
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