in reply to Re: Q: NaN again
in thread Q: NaN again

Problem in filtering of user input.
For example. User try to make bid at auction, and enter NaN in "price" field. All standart methods like: $price = sprintf("%.2f", $price); return me NaN But it not so bad. Really bad is: 
if ($price > $user_money) {
   return "You have not enough money". 
}

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Will fail for NaN. I found about 30 "nan holes" in my code after 5.8.4, and I suppose, I found not all of it.

P.S. Sorry for my bad english.

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Re^3: Q: NaN again
by davorg (Chancellor) on Oct 19, 2006 at 12:14 UTC

    Then, as you say, your problem is with filtering user input. When you recieve input from a user, you need to check that it is a valid number and reject (or ignore) it if it isn't.

    --
    <http://dave.org.uk>

    "The first rule of Perl club is you do not talk about Perl club."
    -- Chip Salzenberg

[reply]
      I have a huge amount of old code. About ten megabytes. I can't check all. So, all I need to know - how to disable NaN autosupport in perl 5.8.4+ for amd64 :-)
[reply]
Re^3: Q: NaN again
by syphilis (Archbishop) on Oct 19, 2006 at 12:32 UTC
    P.S. Sorry for my bad english

    That's ok ... no need to apologise for that. But it would really help if you could provide a complete (and simple) perl script that demonstrates one of the problems you are having.

    Support for NaN's does not exist in perl for all architectures/platforms. It would help us to know which architecture and platform you're running.

    Cheers,
    Rob
[reply]
      web # perl -e '$a="nan"; print sprintf("%.2f",$a)'
nan

web # perl -v
This is perl, v5.8.8 built for x86_64-linux
-----
For Win32:
This is perl, v5.8.4 built for MSWin32-x86-multi-thread

perl -e "$a='nan'; print sprintf('%.2f',$a)"
0.00

      [download]
[reply]
[d/l]
        Yep - it's broken on Win32, and the nature of the breakage varies, depending upon which compiler (ie Visual Studio or MinGW) was used to build perl. I submitted a perlbug report about this (assigned a ticket number of 38779) a while back.

        But the example that you've provided fails in the same way, irrespective of whether perl was compiled with Visual Studio 6.0 or MinGW.

        I thought this had been fixed with Visual Studio 7.0 but I still I get (on my perl built with Visual Studio 7.0): 
        F:\>perl -we "$a='nan'; print sprintf('%.2f',$a)"
0.00

        [download]

        Let's face it ... handling of NaN's on Win32 is unreliable. I don't know how you can disable it. You could try re-compiling perl 5.8.8 with the following patch supplied by Jan Dubois in response to my perlbug report. 
        --- pp.c.orig    Wed Mar 22 19:35:45 2006
+++ pp.c    Wed Mar 22 21:43:04 2006
@@ -1732,8 +1732,15 @@
     }
 #endif
     {
+#if defined(NAN_COMPARE_BROKEN) && defined(Perl_isnan)
+      dPOPTOPnnrl;
+      if (Perl_isnan(left) || Perl_isnan(right))
+      RETSETNO;
+      SETs(boolSV(left < right));
+#else
       dPOPnv;
       SETs(boolSV(TOPn < value));
+#endif
       RETURN;
     }
 }
@@ -1808,8 +1815,15 @@
     }
 #endif
     {
+#if defined(NAN_COMPARE_BROKEN) && defined(Perl_isnan)
+      dPOPTOPnnrl;
+      if (Perl_isnan(left) || Perl_isnan(right))
+      RETSETNO;
+      SETs(boolSV(left > right));
+#else
       dPOPnv;
       SETs(boolSV(TOPn > value));
+#endif
       RETURN;
     }
 }
@@ -1884,8 +1898,15 @@
     }
 #endif
     {
+#if defined(NAN_COMPARE_BROKEN) && defined(Perl_isnan)
+      dPOPTOPnnrl;
+      if (Perl_isnan(left) || Perl_isnan(right))
+      RETSETNO;
+      SETs(boolSV(left <= right));
+#else
       dPOPnv;
       SETs(boolSV(TOPn <= value));
+#endif
       RETURN;
     }
 }
@@ -1960,8 +1981,15 @@
     }
 #endif
     {
+#if defined(NAN_COMPARE_BROKEN) && defined(Perl_isnan)
+      dPOPTOPnnrl;
+      if (Perl_isnan(left) || Perl_isnan(right))
+      RETSETNO;
+      SETs(boolSV(left >= right));
+#else
       dPOPnv;
       SETs(boolSV(TOPn >= value));
+#endif
       RETURN;
     }
 }
@@ -2029,8 +2057,15 @@
     }
 #endif
     {
+#if defined(NAN_COMPARE_BROKEN) && defined(Perl_isnan)
+      dPOPTOPnnrl;
+      if (Perl_isnan(left) || Perl_isnan(right))
+      RETSETYES;
+      SETs(boolSV(left != right));
+#else
       dPOPnv;
       SETs(boolSV(TOPn != value));
+#endif
       RETURN;
     }
 }
--- pp_hot.c.orig    Wed Mar 22 19:35:45 2006
+++ pp_hot.c    Wed Mar 22 21:42:38 2006
@@ -306,8 +306,15 @@
     }
 #endif
     {
+#if defined(NAN_COMPARE_BROKEN) && defined(Perl_isnan)
+      dPOPTOPnnrl;
+      if (Perl_isnan(left) || Perl_isnan(right))
+      RETSETNO;
+      SETs(boolSV(left == right));
+#else
       dPOPnv;
       SETs(boolSV(TOPn == value));
+#endif
       RETURN;
     }
 }
--- sv.c.orig    Wed Mar 22 21:47:13 2006
+++ sv.c    Wed Mar 22 21:31:27 2006
@@ -2134,6 +2134,13 @@
        certainly cast into the IV range at IV_MAX, whereas the correc
+t
        answer is the UV IV_MAX +1. Hence < ensures that dodgy boundar
+y
        cases go to UV */
+#if defined(NAN_COMPARE_BROKEN) && defined(Perl_isnan)
+    if (Perl_isnan(SvNVX(sv))) {
+        SvUV_set(sv, 0);
+        SvIsUV_on(sv);
+    }
+    else
+#endif
     if (SvNVX(sv) < (NV)IV_MAX + 0.5) {
         SvIV_set(sv, I_V(SvNVX(sv)));
         if (SvNVX(sv) == (NV) SvIVX(sv)
--- win32/win32.h.orig    Wed Mar 22 19:35:49 2006
+++ win32/win32.h    Wed Mar 22 21:35:54 2006
@@ -210,6 +210,11 @@
 
 #define isnan        _isnan
 
+#if _MSC_VER < 1300
+/* VC6 has broken NaN semantics: NaN == NaN returns true instead of f
+alse */
+#define NAN_COMPARE_BROKEN 1
+#endif
+
 #endif /* _MSC_VER */
 
 #ifdef __MINGW32__        /* Minimal Gnu-Win32 */

        [download]

        I don't know if it will help. Good luck.

        Cheers,
        Rob
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