Michel Hack wrote:
> On Mar 27, 3:55 pm, hanco...@[EMAIL PROTECTED]
wrote:
>> If I understand the Pr of Op correctly, the standard "extended"
>>floating point allows 128 bits, or about 31 digits of precision.
> Actually, the precision of both HFP128 and BFP128 is about 35 digits
> (varies from 33 to 35 for HFP). The exponent of BFP128 (which will
> become a standard IEEE 754 format when the revised (2007) standard
> comes out as expected in a month or two) has a much wider range than
> HFP128 -- but there is (was?) a software-only variant of HFP128 (for
> Fortran, 20 years ago) called XEXP that has the same precision, but
> an even wider exponent range, +/-9860 or so, twice as wide as BFP128.
HFP first came on the 360/85, though without sup****t for DXR.
On machines with extended precision there was software sup****t for
DXR, named IEAXPDXR, and for machines without all instructions were
simulated by IEAXPALL. (The source is available, though I hand
disassembled IEAXPDXR many years ago.) Like short and long precision,
it has a seven bit hex exponent. To make the software simulation
easier, both halves of extended precision have an exponent field,
with the lower half exponent 14 less (possibly wrapped). It has
a 112 bit hex fraction, so I believe between 32 and 33 decimal
digits.
The OS/360 source available through Hercules has the IEAXP routines.
-- glen
|
