[Chicken-hackers] [PATCH] Prevent Chicken from truncating large flonums when compiling

[Peter Bex]

Hi all,

This is a patch and bugreport rolled into one ;)

While testing the "numbers" egg I found out that programs
containing flonum literals can behave differently when compiled
or interpreted.

This turns out to be caused by the fact that Chicken just
uses [sf]printf or gcvt to print flonums while emitting C code.
When nothing else is specified, these use the default
"flonum-print-precision" of 15, which means that any number with
more _decimal_ digits than that get printed in exponential notation,
like this:

#;1> 123456789012345.0
123456789012345.0
#;2> 1234567890123456.0
1.23456789012346e+15

So after (read)ing the literal the compiler then later prints it
back again, but with less precision than was present when reading it.

This behavior can be tweaked by calling (flonum-print-precision N),
which is exactly what the compiler should be doing and what my patch
does.  You can also merge it from the "sjamaan-pending" branch,
it's changeset 6c39851e1504d01b2de05e014f5542913e3e5c5e.

PS: If someone with access to a Windows system is reading this,
there's a sort-of related bug in #691.  I've attached a patch that
needs to be tested to the ticket.

Cheers,
Peter
-- 
http://sjamaan.ath.cx
--
"The process of preparing programs for a digital computer
 is especially attractive, not only because it can be economically
 and scientifically rewarding, but also because it can be an aesthetic
 experience much like composing poetry or music."
                                                        -- Donald Knuth

0001-Do-not-drop-precision-in-flonums-when-compiling.patch
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