>3 bits set in byte

[trisuglow]

I need to write a function:

f( b As Byte ) As Boolean

The function must return True if the value of b has 3 or less bits set. Otherwise, f returns False.

I can achieve this by converting b to a string using binary format then counting the number of '1's in the string, but I'd like to know if there's a more elegant way to do it.

Anyone care to have a go?

[Doctor Luz]

Not elegant but can be done in a single line if you know how to translate this from C++ to VB (I don't know)

if (((b>>7)&1+(b>>6)&1+(b>>5)&1+(b>>4)&1+(b>>3)&1+(b>>2)&1+(b>>1)&1+b&1)<=3) return TRUE;
else
return FALSE;

[riis]

Function f(b As Byte) As Boolean
 
If ((b \ 128) and 1) + ((b \ 64) and 1) + ((b \ 32) and 1) + ((b \ 16) and 1) + ((b \ 8) and 1) + ((b \ 4) and 1) + ((b \ 2) and 1) + (b and 1)  <= 3 then 
  f = True
Else
  f = False
End If
 
End Function

This should work I think

[sql_lall]

you are testing a boolean statement and if true, you return true, if false, u return false. Why not just return the statement:

Function f(b As Byte) As Boolean
 
f=((((b \ 128) and 1) + ((b \ 64) and 1) + ((b \ 32) and 1) + ((b \ 16) and 1) + ((b \ 8) and 1) + ((b \ 4) and 1) + ((b \ 2) and 1) + (b and 1))  <= 3)
 
End Function

Hopefully this should work

[alkatran]

private function BOOLINGWOOOO(byval b as byte)
dim a as byte 'loop variable
dim c as byte 'number of rights

For a = 7 to 0 step -1
if 2^a > b then c = c + 1: b = b - 2^a
next a


^untested, so not sure.

[riis]

Originally posted by sql_lall
you are testing a boolean statement and if true, you return true, if false, u return false.

I know, but I wanted to stay in the same line as Dr. Luz.

[trisuglow]

Thanks to all - these look a lot nicer than my string manipulation.

[kedaman]

fast and elegant way:
y=0!=x&=(x-1);
y+=0!=x&=(x-1);
y+=0!=x&=(x-1);
y+=0!=x&=(x-1);
return y<4;