(j3.2006) decimal floats

[Robert Corbett]

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