#! perl -slw
use strict;

sub bsearch {
    my( $aref, $value ) = @_;
    my( $lo, $hi, $mid ) = ( 0, $#{ $aref } );

    while( $lo <= $hi ) {
		$mid = int( ($lo + $hi) / 2 );
		if(    $value > $aref->[ $mid ] ) {
			$lo = $mid + 1;
		}
		elsif( $value < $aref->[ $mid ] ) {
			$hi = $mid - 1;
		}
		else {
			#Found an exact match so return that index
			return $mid;
		}
 	}
	# Didn't find an exact match so return the index below where we stopped
	# Or if the value is lower than the 
      # lowest element, return 0
	return $aref->[ $mid ] > $value ? $mid - 1 : $mid;
}


my @array = 0 .. 100;

my $iNearest = bsearch \@array, 31.5;

print 31.5, ' : ', $iNearest, ' : ',$array[ $iNearest ];

print "$_ => @{[ bsearch \@array, $_  ]}" 
    for -1, 0, 1, 2, 31.1, 31.999, 50, 98, 99, 100, 101;

__END__
P:\test>bsearch
31.5 : 31 : 31
-1 => 0
0 => 0
1 => 1
2 => 2
31.1 => 31
31.999 => 31
50 => 50
98 => 98
99 => 99
100 => 100
101 => 100