I was browsing the source code of guile 1.8.2 and have couple of trivial
questions. I would be very grateful if you can answer the following
questions.
1) In test-suite/standalone/test-round.c (lines 90-96) we have
/* 2^DBL_MANT_DIG-1
In the past scm_c_round had incorrectly incremented this value, due
to the way that x+0.5 would round upwards (in the usual default
nearest-even mode on most systems). */
x = ldexp (1.0, DBL_MANT_DIG) - 1.0;
assert (x == floor (x)); /* should be an integer already */
here ldexp and floor both return double values. Is it guaranteed that
asserting the equality of two double values will always work? When learning
C, I remember reading somewhere not to rely on such comparisons.
I also do not understand the comment /* should be an integer already */ at
the end of the line. AFAIK both ldexp, floor function return double values
and not integers. Can someone explain the comment?
I am interested in knowing this because guile 1.8.2 fails to build on a
Debian machine using alpha architecture. According to the build log of the
failure (
http://buildd.debian.org/fetch.cgi?&pkg=guile-1.8&ver=1.8.2%2B1-2&arch=alpha&stamp=1188100514&file=log
)
it occurs around this part of the code.
2) The above code uses DBL_MANT_DIG macro. How can I easily find out where
this macro is defined? Is there any book or reference which discuss this
kind of macros. For now I did a grep in /usr/include and found that such a
macro is defined in /usr/include/c++/4.2/limits file. This brings up
another question.
If you are using a macro defined in a standard c++ library header, shouldn't
the file be named test-round.cpp instead of test-round.c?
thanks
raju
--
Kamaraju S Kusumanchi
http://www.people.cornell.edu/pages/kk288/
http://malayamaarutham.blogspot.com/
_______________________________________________
Guile-devel mailing list
Guile-devel@gnu.org
http://lists.gnu.org/mailman/listinfo/guile-devel
