a/sqrt(x)

a/sqrt(x)

Post by t0n » Thu, 16 Oct 2003 20:03:40



hi,
  i need to compute a/sqrt(x) in floating point arithmetic.
if this is done using reciprocal square root, does it introduces
errors .. if all operations are done with 'infinitely precise rounding'
and same no of bits in fractional part?
if yes .. how much precise Rsqrt(x) shud be to do this properly?
thanks,
t0ny
 
 
 

a/sqrt(x)

Post by Glen Herrmannsfeld » Thu, 16 Oct 2003 23:34:33



Quote:> hi,
>   i need to compute a/sqrt(x) in floating point arithmetic.
> if this is done using reciprocal square root, does it introduces
> errors .. if all operations are done with 'infinitely precise rounding'
> and same no of bits in fractional part?
> if yes .. how much precise Rsqrt(x) shud be to do this properly?

The rounding might be different, but it shouldn't be any more in error.

If you are that worried about error, maybe you shouldn't be using floating
point?

-- glen

 
 
 

a/sqrt(x)

Post by t0n » Fri, 17 Oct 2003 21:19:45


hi, thanks
Quote:> The rounding might be different, but it shouldn't be any more in error.

that will be great ..
Quote:> If you are that worried about error, maybe you shouldn't be using floating point?

have to use erroneous fp ;..
i was looking for a way to equate the results (and so errors) of
possible methods, if the error is not more than normal method that'll
be enough..
how this shud be analyzed ?
thanks again ..
 
 
 

1. sqrt function doesn't use FPU sqrt instruction ?

Does sqrt (in libm.a or libmfast.a) use the FPU coprocessor
square root instruction (see page B-53 in the MIPS R4000 User's Manual)
or does it compute it manually ?

I disassembled the executable of a simple program that computes the
square root of a number using sqrt() and found no trace of the
instruction.

Whats up here ?  Somehow I feel like I'm being cheated.

System is Indy R4400, IRIX 5.2.  languaage is Ada.

____________________________________________________________________________
Tom Haberlandt             | Reality's a horde of mice nibbling away in the


____________________________________________________________________________
"I don't speak for my employer."  - Woof !
____________________________________________________________________________

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