https://www.reddit.com/r/programming/comments/3xq2ul/codedive_2015_talk_three_cool_things_about_d/

https://www.facebook.com/dlang.org/posts/1192267587453587

https://twitter.com/D_Programming/status/678989872367988741


Andrei

On Monday, 21 December 2015 at 17:28:51 UTC, Andrei Alexandrescu wrote:
> https://www.reddit.com/r/programming/comments/3xq2ul/codedive_2015_talk_three_cool_things_about_d/
>
> https://www.facebook.com/dlang.org/posts/1192267587453587
>
> https://twitter.com/D_Programming/status/678989872367988741
>
>
> Andrei

In the future, you should put your name in the title as it will probably get more votes that way.

On Monday, 21 December 2015 at 17:28:51 UTC, Andrei Alexandrescu wrote:
> https://www.reddit.com/r/programming/comments/3xq2ul/codedive_2015_talk_three_cool_things_about_d/

Great motivation as always! Thx!

On Monday, 21 December 2015 at 17:28:51 UTC, Andrei Alexandrescu wrote:
> https://www.reddit.com/r/programming/comments/3xq2ul/codedive_2015_talk_three_cool_things_about_d/

By the way, even though I wholeheartedly share your sentiment regarding those "functional" examples, I found it to be an interesting example for the power of modern optimizers that LDC manages to compile this

---
ulong factorial(this n) {
	return n <= 1 ? 1 : n * factorial(n - 1);
}
---

to this:

---
__D4test9factorialFkZm:
    mov eax, 1
    cmp edi, 2
    jb  LBB0_7
    mov ecx, edi
    lea edx, [rdi + 7]
    add edi, -2
    mov eax, 1
    test    dl, 7
    je  LBB0_4
    and edx, 7
    neg edx
    mov eax, 1
    .align  4, 0x90
LBB0_3:
    imul    rax, rcx
    dec rcx
    inc edx
    jne LBB0_3
LBB0_4:
    cmp edi, 7
    jb  LBB0_7
    add rcx, -3
    .align  4, 0x90
LBB0_6:
    lea rdx, [rcx + 3]
    imul    rdx, rax
    lea rax, [rcx + 2]
    lea rsi, [rcx + 1]
    imul    rax, rsi
    imul    rax, rdx
    lea rdx, [rcx - 1]
    imul    rdx, rcx
    lea rsi, [rcx - 2]
    imul    rsi, rdx
    imul    rsi, rax
    lea rax, [rcx - 3]
    lea rdx, [rcx - 4]
    imul    rax, rdx
    imul    rax, rsi
    add rcx, -8
    lea edx, [rcx + 3]
    cmp edx, 1
    ja  LBB0_6
LBB0_7:
    ret
---

Not sure about how it arrives at the crazily unrolled loop, but no recursion in sight anymore.

 — David

On 12/22/15 1:29 PM, David Nadlinger wrote:

> ---
> ulong factorial(this n) {
>      return n <= 1 ? 1 : n * factorial(n - 1);
> }
> ---

Am I missing some new feature here? What does the 'this' mean?

-Steve

On Tuesday, 22 December 2015 at 19:07:55 UTC, Steven Schveighoffer wrote:
> Am I missing some new feature here? What does the 'this' mean?

I have no idea, this must have been some sort of weird copy/paste or auto-correct mistake on my side. It's supposed to be "uint", as in Andrei's talk.

 — David

On 12/22/2015 10:29 AM, David Nadlinger wrote:
> Not sure about how it arrives at the crazily unrolled loop, but no recursion in
> sight anymore.

It's doing tail recursion optimization, which turns the recursion into a loop.
Then the loop is unrolled 8 times.

On 12/21/2015 09:28 AM, Andrei Alexandrescu wrote:
> https://www.reddit.com/r/programming/comments/3xq2ul/codedive_2015_talk_three_cool_things_about_d/
>
>
> https://www.facebook.com/dlang.org/posts/1192267587453587
>
> https://twitter.com/D_Programming/status/678989872367988741
>
>
> Andrei

Two unnecessary pedantic corrections:

- One of the earlier slides has "Voldermort" with an extra 'r'. It should be Voldemort.

- At the end of one of the optimization presentations you said that the behaviour of unsigned integer overflow and *underflow* are well defined. Although what you meant is clear and that I've been using "underflow" in the same meaning until very recently, I now know that underflow is a condition only for floating point types.

Copying from Wikipedia, "Arithmetic underflow can occur when the true result of a floating point operation is smaller in magnitude (that is, closer to zero) than the smallest value representable as a normal floating point number in the target datatype."

Ali

On Wednesday, 23 December 2015 at 01:07:57 UTC, Walter Bright wrote:
> On 12/22/2015 10:29 AM, David Nadlinger wrote:
>> Not sure about how it arrives at the crazily unrolled loop, but no recursion in
>> sight anymore.
>
> It's doing tail recursion optimization, which turns the recursion into a loop.

The recursive call is not quite a tail call by itself, which is what Andrei pointed out using that example. But yes, that's what happens.

> Then the loop is unrolled 8 times.

Sure thing. I was rather surprised to see that happen given that I only compiled with -O1, though, as it seems to be quite an aggressive optimization.

 — David

On Monday, 21 December 2015 at 17:28:51 UTC, Andrei Alexandrescu wrote:
> https://www.reddit.com/r/programming/comments/3xq2ul/codedive_2015_talk_three_cool_things_about_d/
>
> https://www.facebook.com/dlang.org/posts/1192267587453587
>
> https://twitter.com/D_Programming/status/678989872367988741
>
>
> Andrei


Interesting talk :-) Watched it while cooking.