computation of square root & reciprocal

[elecs_gene]

hi
could u guys give me an algorithm for efficient computation of reciprocal & square root for any number betwwen 0 and infinity...

regards

 

[LouisSheffield]

Tell me more about the need ...
Are you going to be programming?
Is this for a hardware design (like an FPGA)?
Is this for some DSP chip that lacks these functions?

Also, what kind of performance are you looking for?

 

[elecs_gene]

hi
actually i am do a hardware implementation of the ALU in fpga/asic..so, i am in search of algorithms which are efficient as well as implementable in hardware..

with regards

 

[LouisSheffield]

There's a nice description at
**broken link removed**

In particular, for both FPGA and DSP solutions, the "Reciprocal Square Root" algorithm is most often implemented. It is a low-impact version of Newton's method.

Added after 18 minutes:

Another thought - the "initial guess" for iterative methods has a great deal to do with convergence.

If you're doing this in floating-point, I suggest using the exponent in a look-up table for the guess.
If it is integer-based, detect the most-significant set bit, and use its square root as the seed.