[Info-vax] VMS Software Q1 '23 Update

[John Dallman]

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