Re: flags in a bitmap

On 2025-07-04 10:06, Bill Allombert wrote:
 > On Thu, Jul 03, 2025 at 06:06:14PM +0200, Ruud H.G. van Tol wrote:

 >> Bill, many thanks for the pointers, I'll explore.
 >>
 >> As an alternative, maybe add a Vecbits() or Vecflags() or such.
 >> No idea if the first bit should have offset 0 or 1.
 >> Only with bittest(), maybe 0?
 >>
 >> my(B=Vecbits([0], 987654321));
 >> Vecbits_put(~B, 7654, v=1);  \\set the bit at offset 7654, by 
default to 1
 >> Vecbits_put(~B, 7654, [1,0,0,1,1]); \\set bits 7654..7658 to [1,0,0,1,1]
 >> my(b=Vecbits_get(B,7654)); \\get bit-7654
 >> my(b=bittest(B,7653)); \\...

 > What I can do is to allow to set/clean a bit in place inside an integer.
 > However this would only work if the integer is large enough.
 >
 > I can do a git branch if you want to test:
 >
 > ? install(bitset,vWL)
 > ? x=2^(2^20);
 > ? forprime(p=2,2^20,bitset(~x,p))
 >   ***   last result computed in 8 ms.
 > ? my(S=0);for(i=0,2^20-1,S+=bittest(x,i));S
 > %16 = 82025
 >   ***   last result computed in 159 ms.

That indeed looks good, and I can test it.

The word "set" is overloaded! :)
(that is why I used "put" in my suggestions)

-- Ruud