At 09:34 AM 10/15/2005 -0700, you wrote:
> > How would you calculate e^(-at) in 32 bit integer math?
> >
> > Why does it need to be integer math?  From your previous post
> > I got the impression this calculation was going to be done at
> > assembly time.
>
>The assembler I'm using only supports integer math. No fractions. No
>floating point. Just integers. So if you put in .36 it becomes 0. 92/256 =
>0. Integer math.

Okay so you imagine a radix point at an appropriate place. You can move
it around after each intermediate calculation with shifts, provided you
don't overflow. Unfortunately, you've got to deal with "C-like" integer
math and don't have access to the full 64-bits of a multiply, only the
least significant 32 bits.

For example, 0.36 might be represented as 0x0002E14 (0.36 * 32768). The
radix point is between the MS 2 bytes and the LS 2 bytes.

>How do you calculate e^(-x) where x is between 1/256 and 192/256 using only
>integer math.

A Taylor series might do it acceptably well.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


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