Re: Floating Decimal Package/Library?

["John H. Lindsay" <jlindsay@kingston.net>]

tmoran@acm.org wrote:

>                           .....          A fixed point type
> *is* an integer.  


Owch!  We've got a terminological problem here;  Sure,
integers (any length or unlimited length) are fixed point in
that the decimal (binory, hexadecimal, ....) point (actual
or virtual) sits in a position fixed with respect to the
units digit or with respect to any fraction digits.  But
other quantities, dollars and cents amounts and currency
conversion and interest rates, and often other commercial
numeric quantities with a fixed number of digit places after
the decimal point (usually, too, with a fixed number before
the decimal point) have this property too.  This must be me
wearing a COBOL or PL/I hat speaking.  The usual work-
around in languages that don't have data types which allow
a fixed number of digit positions after the decimal point
is to carry such quantities as a multiple of the intended
value by a power of ten to allow storage as some sort of
integer, and (painfully) allowing for the multipliers all
through the code.


There's a bit of confusion too about the handling of fixed 

point quantities (of various radices) by compilers.  The
confusion arises because of two views of the meaning of
these -- accurate to within a half a unit of the last digit
shown or stored (the usual scientific view if an error
range is not stated) or totally accurate as shown (a frequent
commercial interpretation).  The former view leads to the
some of the PL/I type conversion rules; the latter leads to
most of the COBOL implementations of handling numeric
operations, and COBOL people to gasp at PL/I and PL/I people
to sputter over COBOL.


John.

-- 
John H. Lindsay                        jlindsay@kingston.net