Some time ago I have suggested to add support to vector
comparisons in D, because this is sometimes useful and in the
modern SIMD units there is hardware support for such operations:
double[] a = [1.0, 1.0, -1.0, 1.0, 0.0, -1.0];
bool[] t = a[] > 0;
assert(t == [true, true, false, true, false, false]);
Usable instructions like (here shows the intrinsic):
http://msdn.microsoft.com/en-us/library/11dy102s%28v=vs.80%29.aspx
Now on Reddit I have found a small discussion about a slides pack
by Intel:
http://www.reddit.com/r/programming/comments/ym8m6/parallel_programming_for_c_and_c_done_right/
The slides:
https://speakerdeck.com/u/multicoreworld/p/james-reinders-intel-united-states
Link to the PDF:
https://speakerd.s3.amazonaws.com/presentations/5006069136af010002005325/Reinders_KEYNOTE_C_done_right.pdf
At page 69 of those slides there is some code that looks
interesting, I think this is a reduced version of part of it,
that shows another way to use vectorized comparisons:
void main() {
double[] a = [1.0, 1.0, -1.0, 1.0, 0.0, -1.0];
double[] b = [10, 20, 30, 40, 50, 60];
double[] c = [1, 2, 3, 4, 5, 6];
if (a[] > 0)
b[] += c[];
}
I think that code is semantically equivalent to:
void main() {
double[] a = [1.0, 1.0, -1.0, 1.0, 0.0, -1.0];
double[] b = [10, 20, 30, 40, 50, 60];
double[] c = [1, 2, 3, 4, 5, 6];
foreach (i; 0 .. a.length)
if (a[i] > 0)
b[i] += c[i];
}
After that code b is:
[11, 22, 30, 44, 50, 60]
This means the contents of the 'then' branch of the vectorized
comparison is done only on items of b and c where the comparison
has given true.
This looks useful. Is it possible to implement this in D, and do
you like it?
Bye,
bearophile
