Please note that, as implied in the post above, the log scale generator is actually a cheat, based on noticing that the input & output ranges specified happened to lend themselves to a simplified calculation. Ie. log( 8000 ) + 1 is very close to 10.

However, that means that genLogScaler() is basically ignoring most of its input parameters and thus won't work for the generic case.

Here's a fixed version that works for your case and (a couple of other tested examples of) the generic case:

#! perl -slw
use strict;

sub genScaler {
    my( $minout, $maxout, $minin, $maxin ) = @_;
    my $outRange = $maxout - $minout;
    my $inRange = $maxin - $minin;
    my $factor = $inRange / $outRange;
    sub {
        my $in = shift;
        return $minout + ( $in / $factor );
    }
}

sub genLogScaler {
    my( $minout, $maxout, $minin, $maxin ) = @_;
    my $outRange = $maxout - $minout;
    my $inRange = log( $maxin - $minin );
    my $factor = $inRange / $outRange;
    sub {
        my $in = shift;
        $in = 1 if $in < 1;
        return $minout + ( log( $in ) / $factor );
    }
}

my $fscale = genScaler( 1, 10, 0.1, 8000 );

print "Linear:";
printf "%7.1f -> %.1f\n", $_, $fscale->( $_ ) for 0.1, 1, 10, 100, 800
+, 1000, 4000, 6000, 8000;

print "\nLog";
my $lscale = genLogScaler( 1, 10, 0.1, 8000 );

printf "%7.1f -> %.1f\n", $_, $lscale->( $_ ) for 0.1, 1, 10, 100, 800
+, 1000, 4000, 6000, 8000;

print "\nNother Log:";
my $lscale2 = genLogScaler( -5, +5, 0.1, 8000 );
printf "%7.1f -> %.1f\n", $_, $lscale2->( $_ ) for 0.1, 1, 10, 100, 80
+0, 1000, 4000, 6000, 8000;

print "\nNother Log:";
my $lscale3 = genLogScaler( 0, +1000, 0.1, 8000 );
printf "%7.1f -> %.1f\n", $_, $lscale3->( $_ ) for 0.1, 1, 10, 100, 80
+0, 1000, 4000, 6000, 8000;
[download]

Produces:

C:\test>genScalar.pl
Linear:
    0.1 -> 1.0
    1.0 -> 1.0
   10.0 -> 1.0
  100.0 -> 1.1
  800.0 -> 1.9
 1000.0 -> 2.1
 4000.0 -> 5.5
 6000.0 -> 7.8
 8000.0 -> 10.0

Log
    0.1 -> 1.0
    1.0 -> 1.0
   10.0 -> 3.3
  100.0 -> 5.6
  800.0 -> 7.7
 1000.0 -> 7.9
 4000.0 -> 9.3
 6000.0 -> 9.7
 8000.0 -> 10.0

Nother Log:
    0.1 -> -5.0
    1.0 -> -5.0
   10.0 -> -2.4
  100.0 -> 0.1
  800.0 -> 2.4
 1000.0 -> 2.7
 4000.0 -> 4.2
 6000.0 -> 4.7
 8000.0 -> 5.0

Nother Log:
    0.1 -> 0.0
    1.0 -> 0.0
   10.0 -> 256.2
  100.0 -> 512.4
  800.0 -> 743.8
 1000.0 -> 768.6
 4000.0 -> 922.9
 6000.0 -> 968.0
 8000.0 -> 1000.0
[download]

But note: it still contains the hack-y $in = 1 if $in < 1; fix.