Re: Bit rotation question/challenge
On Saturday, 30 January 2021 at 14:56:14 UTC, burt wrote:
On Saturday, 30 January 2021 at 14:41:59 UTC, Afgdr wrote:
On Saturday, 30 January 2021 at 14:40:49 UTC, Afgdr wrote:
On Saturday, 30 January 2021 at 13:30:49 UTC, burt wrote:
[...]
cast as uint and shift. cast the result as ubyte[4].
obiously, that works for n=4 with uint and n=8 for ulong, only.
Yes I used to do this, but then I needed it for n > 8.
You can try somethink like this:
https://run.dlang.io/is/POQgnb
import std.range : cycle, take, drop;
import std.algorithm : copy;
import std.stdio;
version (LittleEndian)
ubyte[n] rotateRight(size_t n)(ref const ubyte[n] array, uint
rotation){
typeof(return) result;
array[]
.cycle()
.drop(n - (rotation / 8) % n)
.take(n)
.copy(result[]);
const ubyte bit_rotation = rotation % 8;
enum ubyte full = 0b_;
if(bit_rotation == 0)
return result;
ubyte next_prefix(const ubyte elm){
const ubyte suffix = (elm & ~(full << bit_rotation));
const ubyte prefix = cast(ubyte)(suffix << (8 -
bit_rotation));
return prefix;
}
ubyte prefix = next_prefix(result[$-1]);
foreach(ref ubyte elm; result[]){
const new_prefix = next_prefix(elm);
elm = (elm >> bit_rotation) | prefix;
prefix = new_prefix;
}
return result;
}
void main(){
ubyte[4] x = [
0b00011000,
0b0011,
0b00010101,
0b0010,
];
writefln!"%(%8b,\n%)"(x.rotateRight(4));
}
Re: Bit rotation question/challenge
On Saturday, 30 January 2021 at 14:56:14 UTC, burt wrote: On Saturday, 30 January 2021 at 14:41:59 UTC, Afgdr wrote: On Saturday, 30 January 2021 at 14:40:49 UTC, Afgdr wrote: On Saturday, 30 January 2021 at 13:30:49 UTC, burt wrote: [...] cast as uint and shift. cast the result as ubyte[4]. obiously, that works for n=4 with uint and n=8 for ulong, only. Yes I used to do this, but then I needed it for n > 8. As suggested in the other answer BitArray may be the best generic solution.
Re: Bit rotation question/challenge
On Saturday, 30 January 2021 at 14:41:59 UTC, Afgdr wrote: On Saturday, 30 January 2021 at 14:40:49 UTC, Afgdr wrote: On Saturday, 30 January 2021 at 13:30:49 UTC, burt wrote: [...] cast as uint and shift. cast the result as ubyte[4]. obiously, that works for n=4 with uint and n=8 for ulong, only. Yes I used to do this, but then I needed it for n > 8.
Re: Bit rotation question/challenge
On Saturday, 30 January 2021 at 14:17:06 UTC, Paul Backus wrote:
On Saturday, 30 January 2021 at 13:30:49 UTC, burt wrote:
[...]
Now I want to bit-rotate the array as if it is one big integer.
You may find `std.bitmanip.BitArray` useful for this:
http://phobos.dpldocs.info/std.bitmanip.BitArray.html
Thank you, this is indeed what I am looking for!
For future reference, this is how I implemented it:
```d
ubyte[n] rotateRight(size_t n)(ubyte[n] x, uint rotation)
{
import std.bitmanip : BitArray;
ubyte[n] x2;
foreach (i, value; x) // have to swap because of endianness
x2[n - 1 - i] = value;
auto copy = x2;
auto bitArray1 = BitArray(cast(void[]) x2[], n * 8);
auto bitArray2 = BitArray(cast(void[]) copy[], n * 8);
bitArray1 >>= rotation;
bitArray2 <<= n * 8 - rotation;
bitArray1 |= bitArray2;
foreach (i, value; x2) // swap back
x[n - 1 - i] = value;
return x;
}
ubyte[4] x = [
0b00011000,
0b0011,
0b00010101,
0b0010,
];
writefln!"%(%8b,\n%)"(x.rotateRight(4));
```
Re: Bit rotation question/challenge
On Saturday, 30 January 2021 at 14:40:49 UTC, Afgdr wrote:
On Saturday, 30 January 2021 at 13:30:49 UTC, burt wrote:
I have a static array of `ubyte`s of arbitrary size:
```d
ubyte[4] x = [ // in reality, ubyte[64]
0b1000,
0b0001,
0b00010101,
0b0010,
];
```
Now I want to bit-rotate the array as if it is one big
integer. So:
```d
ubyte[n] rotateRight(size_t n)(ref const ubyte[n] array, uint
rotation)
{
// ?
}
// same for rotateLeft
ubyte[4] y = [
0b1001,
0b0100,
0b,
0b10001010,
];
assert(x.rotateRight(9) == y);
assert(y.rotateLeft(9) == x);
```
Any ideas how this could be achieved? I.e. what should go at
the "?" for rotateRight and rotateLeft?
cast as uint and shift. cast the result as ubyte[4].
obiously, that works for n=4 with uint and n=8 for ulong, only.
Re: Bit rotation question/challenge
On Saturday, 30 January 2021 at 13:30:49 UTC, burt wrote:
I have a static array of `ubyte`s of arbitrary size:
```d
ubyte[4] x = [ // in reality, ubyte[64]
0b1000,
0b0001,
0b00010101,
0b0010,
];
```
Now I want to bit-rotate the array as if it is one big integer.
So:
```d
ubyte[n] rotateRight(size_t n)(ref const ubyte[n] array, uint
rotation)
{
// ?
}
// same for rotateLeft
ubyte[4] y = [
0b1001,
0b0100,
0b,
0b10001010,
];
assert(x.rotateRight(9) == y);
assert(y.rotateLeft(9) == x);
```
Any ideas how this could be achieved? I.e. what should go at
the "?" for rotateRight and rotateLeft?
cast as uint and shift. cast the result as ubyte[4].
Re: Bit rotation question/challenge
On Saturday, 30 January 2021 at 13:30:49 UTC, burt wrote: I have a static array of `ubyte`s of arbitrary size: ```d ubyte[4] x = [ // in reality, ubyte[64] 0b1000, 0b0001, 0b00010101, 0b0010, ]; ``` Now I want to bit-rotate the array as if it is one big integer. You may find `std.bitmanip.BitArray` useful for this: http://phobos.dpldocs.info/std.bitmanip.BitArray.html
Bit rotation question/challenge
I have a static array of `ubyte`s of arbitrary size:
```d
ubyte[4] x = [ // in reality, ubyte[64]
0b1000,
0b0001,
0b00010101,
0b0010,
];
```
Now I want to bit-rotate the array as if it is one big integer.
So:
```d
ubyte[n] rotateRight(size_t n)(ref const ubyte[n] array, uint
rotation)
{
// ?
}
// same for rotateLeft
ubyte[4] y = [
0b1001,
0b0100,
0b,
0b10001010,
];
assert(x.rotateRight(9) == y);
assert(y.rotateLeft(9) == x);
```
Any ideas how this could be achieved? I.e. what should go at the
"?" for rotateRight and rotateLeft?
