[Cfp-interest] Fw: ISO/IEC JTC 1/SC 22/WG 14 New documents available on ISOTC eCommittee - short float

[Ian McIntosh]

I think adding short float is a good idea, as long as it doesn't interfere
with _Float16 where that's available and as long as it's either optional or
can be implemented as binary32 where there's no hardware support for
anything smaller (as section 4.1 allows).

ARM has 2 __fp16 types.  One is binary16.  One is not, having a slightly
bigger exponent range instead of Infinities and NaNs (like the CELL SPUs).

Nvidia half is the same as binary16.  I think half2 is a vector of 2 half
s, getting 2x speed.

OpenEXR HALF is almost the same as binary16, except only supporting the
default rounding mode.

In section 3.1 "_Float16 . . . The specification is general in that it can
handle a wide range of lengths. However, it only permits an exact size."

That's true, but _Float16x allows any other representation with (1) IEEE
semantics including Infinities and NaNs, (2) at least the exponent range of
_Float16, and (3) at least the precision of _Float16.  That might handle
some of the other "half" precision variants listed in section 2.3.  It
might handle TI's 20 bit.  It would not handle OpenGL's 10 or 11 bit (or
14, which I was unable to find in the OpenGL spec) and maybe not TI's 20
bit.

In section 2.1, Adobe also has 24 bit floating-point, not just 16.

In section 5.4, should promotion be to float except where float would be
promoted to double?  On many CPUs, "float f; short float sf; . . . f+sf"
would be faster when evaluated as a float than as a double.  Some CPUs/GPUs
process half or half2 precision up to twice as fast as single precision, so
is promotion necessary on them?

- Ian McIntosh          IBM Canada Lab         Compiler Back End Support
and Development




From:	"Rajan Bhakta" <rbhakta at us.ibm.com>
To:	cfp-interest at oakapple.net
Date:	2016-03-14 12:44 PM
Subject:	[Cfp-interest] Fw: ISO/IEC JTC 1/SC 22/WG 14 New documents
            available on ISOTC eCommittee
Sent by:	cfp-interest-bounces at oakapple.net



FYI, this new document is being brought up for the next WG14 meeting by
another group.

One point I want to make is in 3.1 the _Float16x (which we do *not* specify
in Part 3 of the TS) may be appropriate in some cases, but the
"readability" argument and non-IEEE argument is still there.



Regards,

Rajan Bhakta
z/OS XL C/C++ Compiler Technical Architect
ISO C Standards Representative for Canada
C Compiler Development
Contact: rbhakta at us.ibm.com, Rajan Bhakta/Houston/IBM
----- Forwarded by Rajan Bhakta/Houston/IBM on 03/14/2016 10:08 AM -----

From:        Daniel Plakosh <livelinkisotc at iso.org>
To:        Rajan Bhakta/Houston/IBM at IBMUS
Date:        03/14/2016 09:18 AM
Subject:        ISO/IEC JTC 1/SC 22/WG 14 New documents available on ISOTC
eCommittee



Dear member,

Please note that the following new documents have been posted
on the ISO/IEC JTC 1/SC 22/WG 14 eCommittee:

                                                    
   N    Title (Description) Exp.   Due   Version    
 Number                     Action Date  Date       
                                                    
  2016  Adding Fundamental  INFO   None  2016-03-14 
        Type for Short                              
        Float                                       
                                                    
                                                    
                                                    
  2011  ISO/IEC TS 17961    INFO   None  2016-03-14 
        with TC1                                    
        Incorporated                                
                                                    
                                                    
                                                    




Download all documents as ZIP : ZIP-File

Access to ISO/IEC JTC 1/SC 22/WG 14 : Committee Homepage


Please inform us if you have any difficulty accessing the above documents.
For help with technical
problems please contact helpdesk at iso.org .

Best regards

dplakosh at cert.org

[attachment
"ISO-IECJTC1-SC22-WG14_N2016_Adding_Fundamental_Type_for_Shor.pdf" deleted
by Ian McIntosh/Toronto/IBM]
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