Thanks to Scott Dottalo who replied to my query by email; he said:

>P.S. I didn't post this to the list because I think the code is
>too long. If you think otherwise, or if you think someone else may
>benefit, then feel free to post it.

>A linear transfer function is extremely common in A/D
>applications. I've used them in several instances to
>compensate/calibrate hardware. In my experience, the general
>purpose floating point computations have been too slow. Similarly,
>I suspect the BCD computations you allude to will also be slow.

Speed is not a problem for the current project, as the display
update interval can be as long as 1 second. Assuming a 4 MHz
clock, ie. 1 usec instruction cycle, a 24-bit f/p multiply would
take 313 usecs maximum according to app note AN575. A complete
calulation using several milliseconds would be perfectly ok.

What I'm looking for is the kind of routines used in a 4-function
calculator. I'd guess that implementing one of those on a PIC
would not be competitive, although there must be PIC-based special
function calculators.

I started working on an algorithm to convert the floating point
binary to decimal; for instance

    111.111 binary

means 1 + 2 + 4 + 0.5 + 0.25 + 0.125 decimal. The method would
deal with the integer and fractional parts separately, generating
the BCD equivalent of each power of 2 and adding it to a running
total if the bit was 1. Naturally, I'd rather use code (or even an
algorithm) that was already available.

Regards, D.M.

ps. Here's a summary of the routines Scott mentioned:

+-------------------------
;scale_hex2dec
;  The purpose of this routine is to scale a hexadecimal byte to a
;decimal byte.
+-------------------------
;write_byte_as_dec
;
;  The purpose of this routine is to convert a byte to a 3 digit ASCII string
;representing the decimal value of the byte. For example, 0xff = 255 is
converted
;to 0x32 0x35 0x35.
+-------------------------
;BCD_2_ASCII
;
;   The purpose of this routine is to convert the BCD byte in W into two
ASCII bytes.
+-------------------------
;write_word_as_dec
+-------------------------
;BCD_adjust
;
;  This routine will 'adjust' the byte that W points to to BCD. The
;algorithm is based on converting hexadecimal into decimal.
+-------------------------