Re: Making Lemonade (Floating-point format changes)

On 12/05/2024 05:44, John Savard wrote:

I've made another long-overdue change in the Concertina II
architecture on the page about 17-bit instructions.
 Since I describe the individual instructions there, with their opcodes
and what they do, I've illustrated the floating-point formats of the
architecture on that page.
 The good people in charge of the IEEE 754 standard had seen fit to
define a standard 128-bit floating-point format which included a
hidden first bit.
 This annoyed me greatly, because I was going to take the 8087's
temporary real format, and extend the mantissa for my 128-bit format.
 I've decided that it's necessary to fully accept the 128-bit standard
and support it in a consistent manner.
 Therefore, I have taken the following actions:
 I have dropped the option of supporting 80-bit temporary reals
entirely, as they are now incompatible as an internal format.
 I have instead defined a 256-bit format for floats which does not have
a hidden first bit, which looks like the old temporary reals, except
that the exponent field is one bit wider.
 And in addition, just as the IBM 704 used two single-precision floats
to make a double-precision float, and the IBM System/360 Model 85
started using two double-precision floats to make an extended
precision float... I've defined how the 256-bit internal format floats
can be doubled up to make a 512-bit float.
 I'm not really sure such floating-point precision is useful, but I do
remember some people telling me that higher float precision is indeed
something to be desired. Well, the IEEE 754 standard has forced my
hand.

YES, I'd use something similar:
I never cared nor supported any odd 10 byte formats and I give a fart to all these weird IEEE standards.
my OS and it's calculator support only 2^N data starting with 4bit nibbles up to 512 bit mantissa, both signed and unsigned and optionally added by an 2^N or an x^10 valued exponent (nibble based sizes).
I finally (1998) made all numeric variable types QUAD-based (4,8,12,...)
this made all calculation and input/output routines short/fast and give my clients the option to define their own formats (ie: 12+4, 28+4,...).
I can also use BCD variables, but they belong to text here and were converted to binary on the fly when entered in calculations.
__
wolfgang