A recent Chatterbox comment, got me thinking about all the various ways to do this. Take the square root of 5 to 10000 digits, print it, and return back a 5 in the inverse operation.

My submission:

#!/usr/bin/perl
use warnings;
use strict;
use Math::MPFR qw(:mpfr); 

#use FileHandle;
#STDOUT->autoflush(1);

$|++;

Rmpfr_set_default_prec(10000);
#print Rmpfr_get_default_prec(),"\n"; 

my $rop = Rmpfr_init2(10000); # return   
my $op = Rmpfr_init2(10000);  # operand 
my $flip = Rmpfr_init2(10000);  # return test   
Rmpfr_set_d ($op, 5.0 , GMP_RNDN);                                    
+                       

#Set $rop to the square root of the 2nd arg rounded in the
#direction $rnd. Set $rop to NaN if 2nd arg is negative.
#Return 0 if the operation is exact, a non-zero value otherwise.
my $bool = Rmpfr_sqrt($rop, $op, GMP_RNDN);
print "$bool\n";
if($bool == 0){print "Exact\n";}

print "$rop\n\n"; # dosn't print 10000 digits unless asked for
print "length ",length $rop,"\n\n";

#my $s3 = Rmpfr_get_str($rop,10,0, GMP_RNDD);
#the 0 means print as many digits needed to be exact
#in the reverse operation
 
# actually ask for 10000
my $s3 = Rmpfr_get_str($rop,10,10000, GMP_RNDN); 

print "$s3\n\n";
print "length ", length $s3,"\n\n\n";

# see if return is accurate
#Set $flip to the square of $op, rounded in direction $rnd.
my $si = Rmpfr_sqr($flip, $rop, GMP_RNDN );

print "go back\n";
print "$flip\n";
# pretty close :-)
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