(j3.2006) decimal floats
Robert Corbett
Robert.Corbett
Sun Jan 13 23:45:14 EST 2008
Andy Vaught wrote:
> On Fri, 11 Jan 2008, Robert Corbett wrote:
>
>
>>I agree that implicit conversions should be banned. There should be
>>functions for explicit conversions. I suspect that most people do not
>>understand how expensive radix conversions are, especially for large
>>exponents.
>>
>>Some people on the committee think arithmetic should be done in the
>>format used to represent values in memory. That could create problems
>>for programs that use IEEE 754r's storage format such as binary16 and
>>decimal32.
>
>
> The parsing and printing of binary numbers to and from ascii is a prime
> example of radix conversion.
>
> The fortran philosophy of the past, however, is that you can even
> interoperate reals and integers without explicit conversion. Or even
> adding reals to logicals on some implementations. If people are concerned
> about speed, they're going to figure out not to do a conversion pretty
> quick, and, IMO, not use decimal arithmetic at all.
The cost of radix conversions is much greater than the cost of integer
to floating-point and floating-point to integer conversions. At some
point, a quantitative difference becomes a qualitative difference.
The cost of doing radix conversions during formatted I/O is high,
especially when the conversions are required to be accurate to the
last digit.
Bob Corbett
More information about the J3
mailing list