Re: logical and ????

[Matthew Flax]

On 12 December 2001, Paul Kienzle wrote:
> Thanks to Kai Habel, we have bitand, bitor, etc. as
> oct-files in octave-forge at http://octave.sf.net
> but limited to 32 bits.
> 
> I can replace all of the bit functions with m-file
> implementations using arithmetic (+,-,*,/) except 
> for bitand.  If I can figure out bitand, then we
> can use all the bits of the mantissa for a double
> (which is 53 bits I believe).  Any suggestions?
> 
> bitxor(a,b)   : (a - bitand(a,b)) + (b - bitand(a,b))
> bitor(a,b)    : (a - bitand(a,b)) + b
> bitset(a,n)   : a + sum(2.^n)
> bitset(a,n,0) : a - bitand(a,sum(2.^n))
> bitget(a,n)   : bitand(a,2^n) != 0 
> bitshift(a,k) : fix (a * 2^k)
> bitcmp(a)     : (2.^bitmax - 1) - a

Wow thats a great idea. 

> 
> Paul Kienzle
> address@hidden
> 
> On Tue, Dec 11, 2001 at 10:40:05PM -0600, John W. Eaton wrote:
> > On 12-Dec-2001, Matthew Flax <address@hidden> wrote:
> > 
> > | When I  try the following I get a confusing answer :
> > | 
> > | octave:47> 0x4 & 0x8
> > | ans = 1
> > | 
> > | surely that should be ans=0 ?
> > 
> > No.  The & and | operators work element-by-element for matrices.  Your
> > 0x4 and 0x8 numbers are just scalars, so the result is 1, which tells
> > you that both elements in the comparison are nonzero.  If you want
> > bit-wise operations, you need some functions to do it.  The matcompat
> > package may have some, but they aren't distributed as a part of Octave
> > (yet).
> > 
> > jwe
> > 
> > 
> > 
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-- 
Matt

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