[perl #19500] [PATCH] fix to disallow negative zero

[via RT]

# New Ticket Created by  Michael Joyce 
# Please include the string:  [perl #19500]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt2/Ticket/Display.html?id=19500 >


Hello.

The core parrot op neg() allows zero to become negative. That shouldn't 
happen. I've attached a patch to this email that corrects the problem by 
testing if neg() was passed a value of zero. I've also attached a patch that 
adds a new test to make sure that zero cannot become negative.

See also http://mathworld.wolfram.com/CountingNumber.html (zero is neither 
positive nor negative)

Michael.

PS. I hope I've done this right. Please let me know if I didn't.

-- attachment  1 ------------------------------------------------------
url: http://rt.perl.org/rt2/attach/46352/36351/45ddee/core.ops.patch

-- attachment  2 ------------------------------------------------------
url: http://rt.perl.org/rt2/attach/46352/36352/1d39c1/number.t.patch


Index: core.ops
===================================================================
RCS file: /cvs/public/parrot/core.ops,v
retrieving revision 1.240
diff -u -r1.240 core.ops
--- core.ops	27 Dec 2002 09:33:11 -0000	1.240
+++ core.ops	27 Dec 2002 21:25:37 -0000
@@ -1703,21 +1703,29 @@
 =cut
 
 inline op neg(inout INT) {
+  if($1 == 0.0)
+    goto NEXT();
   $1 = -($1);
   goto NEXT();
 }
 
 inline op neg(inout NUM) {
+  if($1 == 0.0)
+    goto NEXT();
   $1 = -($1);
   goto NEXT();
 }
 
 inline op neg(out INT, in INT) {
+  if($2 == 0.0)
+    goto NEXT();
   $1 = -($2);
   goto NEXT();
 }
 
 inline op neg(out NUM, in NUM) {
+  if($2 == 0.0)
+    goto NEXT();
   $1 = -($2);
   goto NEXT();
 }

Index: t/op/number.t
===================================================================
RCS file: /cvs/public/parrot/t/op/number.t,v
retrieving revision 1.27
diff -u -r1.27 number.t
--- t/op/number.t	14 Dec 2002 01:17:04 -0000	1.27
+++ t/op/number.t	27 Dec 2002 21:26:41 -0000
@@ -1,6 +1,6 @@
 #! perl -w
 
-use Parrot::Test tests => 36;
+use Parrot::Test tests => 37;
 use Test::More;
 
 output_is(<<CODE, <<OUTPUT, "set_n_nc");
@@ -885,6 +885,16 @@
     end
 CODE
 -3.000000
+OUTPUT
+
+output_is(<<CODE, <<OUTPUT, "neg 0.0");
+    set N1, 0
+    neg N1
+    print N1
+    print "\\n"
+    end
+CODE
+0.000000
 OUTPUT
 
 output_is(<<CODE, <<OUTPUT, "mul_n_n");