> On 08 Jun 2015, at 4:41 , Matthieu Lacaton <matthieu.laca...@gmail.com> wrote:
>
> Hello everyone,
>
> I have a small question about NativeBoost : How does the "+" operator when
> applied to a pointer translates into NativeBoost code ?
>
> To give a bit of context, what I want to do is to reallocate some
> non-contiguous bytes in memory to a buffer. Basically, I have an array of
> integers in a buffer and I want to copy some chunks of it in another buffer.
> The chunks are always the same size and the offset between each chunk is
> always the same too.
>
> Because a bit of actual code is easier to understand here is what I'd like to
> do in Pharo :
>
> ...
>
> int i, j;
> int *data = malloc(1000*sizeof(int));
> int *newData = malloc(50*sizeof(int));
>
> // Allocate initial data
> for (i = 0 ; i < 1000, i++) {
> data[i] = i;
> }
>
> //Copy desired chunks into new buffer
> for (i = 0; i < 5; i++ ) {
> memcpy( newData + j*10, data + 200 + j*30, 10*sizeof(int));
> j++;
> }
>
> free(data);
You can do relative addressing like this:
(destReg ptr: dataSize) + offsetReg + constant
So with offSetRegs containing j* 10 and j* 30, you might end up with an
unrolled inner loop (barring using any fancier longer-than-int moves) like:
0 to: 9 do: [:constantOffset |
asm mov: (destReg ptr: currentPlatform sizeOfInt) + dstOffsetReg +
constantOffset with: (srcReg ptr: currentPlatform sizeOfInt) + 200 +
srcOffsetReg + constantOffset]
If the range of j is constant, you can just as easily unroll the whole thing in
a similarly compact fashion, space and sensibilites permitting:
0 to: 4 do: [ :j | 0 to: 9 do: [ :consOffset |
asm mov: (destReg ptr: currentPlatform sizeOfInt) + (j* 10) +
constOffset with: (srcReg ptr: currentPlatform sizeOfInt) + 200 + (j * 30) +
constOffset]
Cheers,
Henry
