Re: [Jsoncpp-devel] Backwards incompatible change in jsoncpp 64-bit support

[Baptiste L. <bap...@gm...>]

2011/5/25 Aaron Jacobs <ja...@go...>

> Hmm, but does it make sense to say a default constructed value is all
> of null, an array, and an object? Wouldn't it make more sense to have
> isArray (and only isArray) start returning true once the value is
> "turned into" an array by appending something to it?
>
> I'd appreciate if you could investigate the VC++ issues; I don't have
> easy access to a Windows machine.
>

The unit test failures are real strange:

   double x = kint64max;
   double y = val.asDouble();
   int count = 0;
   if ( y == x ) // OK (case 1)
   {
       ++count;
   }
   if ( double(kint64max) == y ) // BAD (case 2)
   {
       ++count;
   }

Looking at the assembly, the only difference I see is that in the first case
the x value (kint64max) is loaded from the local variable, while in the
second case it never leave the FPU register if I understand correctly. My
guess is that we are stumbling into the fact that FPU register have an
internal precision of 80 bits. I'm not sure how to confirm this though...

Case 1:
   if ( y == x )
00411B97  fld         qword ptr [ebp-290h]
00411B9D  fcomp       qword ptr [ebp-2A0h]
00411BA3  fnstsw      ax

Case 2:
   if ( double(kint64max) == y )
00411BB9  call        std::numeric_limits<__int64>::max (412D60h)
00411BBE  mov         dword ptr [ebp-0A4Ch],eax
00411BC4  mov         dword ptr [ebp-0A48h],edx
00411BCA  fild        qword ptr [ebp-0A4Ch]
00411BD0  fcomp       qword ptr [ebp-2A0h]
00411BD6  fnstsw      ax

I worked-around this by making code match case 1...


There is another kinds of test failures that occurs related to how floating
pointer number are represented as string. With MSVS AFAIK we always get
three digits in the exponent. Here are some examples of failures:

1>* Detail of ValueTest/integers test failure:
1>..\..\src\test_lib_json\main.cpp(582): "1.04858e+06" == val.asString()
1>  Expected: '1.04858e+06'
1>  Actual  : '1.04858e+006'


* Test E:\prg\vc\Lib\jsoncpp-trunk\test\data\test_real_09.json
  Difference in input at line 1:
  Expected: '.=1.9e+19'
  Actual:   '.=1.9e+019'

The easiest is probably to normalize floating point string before
comparison. What do you think?

Baptiste.