Re: long double data type
Re: long double data type
- Subject: Re: long double data type
- From: Alastair Houghton <email@hidden>
- Date: Mon, 14 Jun 2010 19:47:34 +0100
On 14 Jun 2010, at 19:32, Jonas Maebe wrote:
> On 14 Jun 2010, at 20:17, Jens Alfke wrote:
>
>> I’m not an expert on FP math, but I don’t know of any float data type supported on Mac OS with more than 64 bits of precision (aka ‘double’).
>
> "long double" has 128 bit precision on PPC and 80 bits of precision on Intel (in both cases the precision is the same in 32 and 64 bit mode).
Erm, no.
Precision means something very specific in this context, and it *isn't* the same as the size of the type, as I'm sure both of you already know but temporarily forgot when writing these e-mails :-)
For instance, 64-bit IEEE floats have 53 bits of precision, while 128-bit floats have 113, I believe. Intel's 80-bit format has 64 bits of precision.
> To my knowledge, the vector processing units on x86 only support 32-bit floats.
SSE definitely supports 64-bit floats (doubles) as of SSE2, though of course with a 128-bit register you can only pack two per register.
Kind regards,
Alastair.
--
http://alastairs-place.net
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