From: Heesob Park <phasis@...>
Date: 2013-04-25T14:43:13+09:00
Subject: [ruby-core:54573] Re: [ruby-trunk - Bug #8299] Minor error in float parsing

2013/4/25 naruse (Yui NARUSE) <naruse@airemix.jp>:
>
> Issue #8299 has been updated by naruse (Yui NARUSE).
>
>
> phasis68 (Heesob Park) wrote:
>> 2013/4/25 naruse (Yui NARUSE) <naruse@airemix.jp>:
>>  > Therefore use SSE2 rather than such workaround.
>>
>>  I'm not sure why you think SSE2 can fix this issue.
>>
>>  The ruby_strtod function used in converting string value to double
>>  value requires double-precision (53-bit) rounding precision but
>>  mingw32 gcc 4.5.2 have default 64-bit precision which higher than
>>  other compilers.
>>
>>  So the patch lowers precision from 64 bit to 53 bit.
>
> double arithmetics with SSE2 is double-precision.
> see also gcc's -mfpmath=sse option
> http://gcc.gnu.org/onlinedocs/gcc-4.0.0/gcc/i386-and-x86_002d64-Options.html#index-march-959

I agree that SSE2 is the better solution for modern OS and modern compiler.

But SSE2 has more restrictions than x87.
SSE2 is not supported on the following environment.
   Microsoft Visual C++ Compiler prior to Visual Studio .NET 2003.
   AMD CPUs prior to Athlon 64, including all Socket A-based CPUs
   Intel CPUs prior to Pentium 4