Definitions of "quantum" and "preferred exponent"

[Michel Hack (1-914-784-7648) <hack@xxxxxxxxxxxxxx>]

>  quantum: The quantum of a finite floating-point representation is
>  the value of a unit in the last position of its significand. This
>  is equal to the radix raised to the exponent q.

This is correct.  Note that "exponent q" denotes the integer-view
exponent, not the scientific-view "exponent e", where q=e+1-p and
p is the precision (7, 16 or 34 digits).

> The definition of "preferred exponent" is also strange (what does
> "which best preserves the quantum of the operands" mean?).

Some have argued for "preferred quantum", but it may have been too
late for a pervasive change in the document.  It is indeed easier
to describe operations in terms of quantum preservation, which can
be thought of as the "units" in which quantities are expressed.

Michel.
Sent: 2007-09-25 14:20:19 UTC