On Mon, 04 Jul 2011 14:03:35 -0400, Christian Manning
<[email protected]> wrote:
Hi, when I populate a BitArray using .init, the bits are in reverse
order, although the bytes are in the correct order.
eg:
import std.stdio,std.bitmanip;
void main() {
ubyte[] arr = [130,56,43,2];
BitArray ba;
ba.init(cast(void[])arr,32);
foreach(b; ba)
write(cast(ubyte) b); //bits in each byte reversed
//01000001000111001101010001000000
writeln();
ba.init(cast(void[])arr.reverse,32);
foreach(b; ba.reverse)
write(cast(ubyte) b); //bits printed in intended order
//10000010001110000010101100000010
writeln();
}
Why does this happen?
What exactly are you expecting? In other words, when using the void[]
version of init, you are specifying the exact memory to use, which implies
you know how BitArray's internals work. If you create a BitArray by
adding bits to the BitArray, then it's internal storage doesn't matter to
you, it can store however it wants.
I'd guess the most logical reason to store the bits in reverse order would
be for performance. Not sure what the merits are, but typically, it's
faster to access and manipulate the 0 bit than some arbitrary bit.
-Steve
