[Info-vax] VMS Software Q1 '23 Update

[Dave Froble]

On 1/29/2023 2:41 PM, John Dallman wrote:
> In article <tr6dje$2s9rm$1 at dont-email.me>, arne at vajhoej.dk (Arne Vajhøj)
> wrote:
>
>> Didn't VAX to Alpha migration cause some issues with D floating?
>>
>> If I remember correct then Alpha did not fully support D.
>
> It didn't support D at all, as best I know. VAX had:
>
> F format is 32-bit single-precision, with 8 exponent bits, 1 sign bit,
> and 23 fraction bits, approximately plus or minus 2.9E-39 to plus or
> minus 1.7E+38, with a precision of approximately seven decimal digits.
> The exponent bias is 128. This format was carried forwards into Alpha.
>
> D format is double-precision, with 8 exponent bits, 1 sign bit, and 55
> fraction bits, approximately plus or minus 2.9E-39 to plus or minus
> 1.7E+38, with a precision of approximately 16 decimal digits. It's F
> format with more precision, but no more range. This format was not
> carried forwards into Alpha, and does not seem to have been much used.
>
> G format is also double-precision, with 11 exponent bits, 1 sign bit, and
> 52 fraction bits, approximately plus or minus 5.6E-309 to plus or minus
> 0.9E+308, with a precision of approximately 15 decimal digits. The
> exponent has a bias of 1,024 (not 128). This format was carried forwards
> into Alpha.
>
> H format is quad-precision, with 15 exponent bits, 1 sign bit, and 112
> fraction bits, approximately plus or minus 8.4E-4933 to plus or minus
> 5.9E+4931, with a precision of approximately 33 decimal digits. The
> exponent has a bias of 16,384 (not 1024). This format was not carried
> forwards into Alpha, although the similar 128-bit X format was provided
> there.
>
> Alpha also had S-format, IEEE single-precision which is similar to F but
> not the same, and T format, IEEE double precision, which is similar to G,
> but likewise not the same. The IEEE formats differ in their exponent
> biases.
>
> S format is 32-bit single-precision, with 8 exponent bits, 1 sign bit,
> and 23 fraction bits, approximately plus or minus 1.18E-39 to plus or
> minus 3.4E+38, with a precision of approximately seven decimal digits.
> The exponent bias is 127, not 128.
>
> T format is double-precision, with 11 exponent bits, 1 sign bit, and 52
> fraction bits, approximately plus or minus 2.2E-308 to plus or minus
> 1.8E+308, with a precision of approximately 16 decimal digits. The
> exponent has a bias of 1,023, not 1,024.
>
> This is summarised from
>
> <https://nssdc.gsfc.nasa.gov/nssdc/formats/VAXFloatingPoint.htm>
>
> John
>

Hmmmm ......

My AlphaServer 800:

AS800> syh
OpenVMS V8.3  on node AS800  29-JAN-2023 17:36:30.33  Uptime  132 06:18:03

Basic help mentions ...

DATA_TYPES

   REAL

      Floating-point values are stored using a signed exponent  and  a  binary
      fraction.   BASIC  allows  six  floating-point formats:  single, double,
      gfloat, sfloat, tfloat, and xfloat.  These  formats  correspond  to  the
      SINGLE, DOUBLE, GFLOAT, SFLOAT, TFLOAT, and XFLOAT keywords.

      Keyword             Range                                  Precision

      SINGLE (32-bit)    .29 * 10^-38 to 1.7 * 10^38              6 digits
      DOUBLE (64-bit)    .29 * 10^-38 to 1.7 * 10^38             16 digits
      GFLOAT (64-bit)    .56 * 10^-308 to .90 * 10^308           15 digits
      SFLOAT (32-bit)   1.18 * 10^-38 to 3.40 * 10^38             6 digits
      TFLOAT (64-bit)   2.23 * 10^-308 to 1.80 * 10^308          15 digits
      XFLOAT (128-bit)  6.48 * 10^-4966 to 1.19 * 10^4932        33 digits

Now, it has been my impression that that DOUBLE is D-float.

Walks like a D-float
Quacks like a D-float
Is it a D-float?

-- 
David Froble                       Tel: 724-529-0450
Dave Froble Enterprises, Inc.      E-Mail: davef at tsoft-inc.com
DFE Ultralights, Inc.
170 Grimplin Road
Vanderbilt, PA  15486