1 |
Darren Dale <dd55@×××××××.edu> (Sat, 22 Oct 2005 14:16:02 -0400): |
2 |
> I am trying to track down the source of a bug in the SciPy development branch |
3 |
> which, so far, has only been reported on a Gentoo platform (mine). It |
4 |
> involves the use of the libc math function "signbit". Here is a clip from the |
5 |
> manpage: |
6 |
> |
7 |
> `signbit' is a generic macro which can work on all real floating- |
8 |
> point types. It returns a non-zero value if the value of X has |
9 |
> its sign bit set. |
10 |
> |
11 |
> On my system, SciPy's signbit function reports that the sign bit is not set |
12 |
> for any number, positive or negative. Could someone here help me understand |
13 |
> how to test the libc signbit function? I have to admit I have no experience |
14 |
> with C programming. |
15 |
|
16 |
Hello Darren, |
17 |
|
18 |
This doesn't have to be a bug. I don't know how SciPy works, but many |
19 |
scientific libraries provide their own number types. In most number |
20 |
encoding schemes (like floating point) the sign of a number is |
21 |
determined by a single bit (the most significant bit of the whole |
22 |
number, for integer types; the most significant bit of the mantissa, for |
23 |
floating point types). |
24 |
|
25 |
The scheme could be totally different for SciPy, so the bit actually |
26 |
reported might be the wrong bit. This is not a bug, but rather a |
27 |
missing feature (signbit() doesn't know the type of the number). |
28 |
|
29 |
Regards. |
30 |
|
31 |
|
32 |
|
33 |
----- |
34 |
Get my public key via GnuPG with one of: |
35 |
gpg --keyserver subkeys.pgp.net --recv-keys CE402012 |
36 |
gpg --keyserver ldap://keyserver.pgp.com/ --recv-keys CE402012 |
37 |
|
38 |
Or via web-based keyserver: |
39 |
http://www.keyserver.de/ |
40 |
|
41 |
Key fingerprint: |
42 |
0F12 0912 DFC8 2FC5 E2B8 A23E 6BAC 998E CE40 2012 |