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Topic: Fast exponent and logarithm, given initial estimate
Replies: 29   Last Post: Nov 8, 2004 2:31 AM

 Messages: [ Previous | Next ]
 Martin Brown Posts: 259 Registered: 12/13/04
Re: Fast exponent and logarithm, given initial estimate
Posted: Oct 19, 2004 4:40 AM

&lt;glenlow@pixelglow.com&gt; writes

&gt;I need a fast exponent and logarithm routine for floats. It should
&gt;preferably use only adds, subtracts and multiplies; divides and square
&gt;roots are permissible if necessary. It should not use large lookup
&gt;tables. An additional wrinkle (or help) is that there's a exponent and
&gt;a logarithm estimate available. (In case you're wondering, this is the
&gt;situation with the Altivec SIMD instruction set.)

Log(1+x) ~ x(6+x)/(6+4x)

Might be of some use depending on how fast your divide is (for small x)

You also need to specify how accurate the log(x) and exp(x) must be -
fastest methods that cut corners for speed are not necessarily as
accurate.

Regards,
--
Martin Brown

Date Subject Author
10/18/04 Glen Low
10/18/04 Jeremy Watts
10/19/04 Peter Spellucci
10/19/04 Glen Low
10/18/04 bv
10/19/04 Glen Low
10/19/04 George Russell
10/19/04 Glen Low
10/20/04 George Russell
10/20/04 Glen Low
10/21/04 Christer Ericson
10/21/04 Glen Low
10/22/04 Christer Ericson
10/19/04 Martin Brown
10/19/04 Glen Low
10/19/04 Richard Mathar
10/19/04 Glen Low
10/20/04 Gert Van den Eynde
10/20/04 Glen Low
10/20/04 Richard Mathar
10/21/04 Gert Van den Eynde
10/21/04 bv
10/22/04 Glen Low
10/22/04 Peter Spellucci
10/22/04 Glen Low
10/23/04 bv
10/24/04 Gert Van den Eynde
10/25/04 Peter Spellucci
10/20/04 Gert Van den Eynde
11/8/04 Glen Low