My perl has them: 
#perl -e 'use Config;print "long doubles\n" if $Config{d_longdbl} eq "
+define";'
long doubles

[download]
But they are not default:- 
# perl -e 'use Config;if ($Config{uselongdouble} eq "define") {print "
+long doubles by default\n";} else {print "not default? How to use???\
+n"}'
not default? How to use???

[download]
So how do I force their use?

I do not want to use external modules, and yes, I know all about base-2 and float precision.

In reply to How do I use "Long Doubles" in perl? by cnd

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