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digitalmars.D.ldc - Why LDC drop d_with_sum code? (windows)

reply KnightMare <black80 bk.ru> writes:
https://forum.dlang.org/post/zpqkgldjlozfnmsveqkn forum.dlang.org

DMD & LDC change d_with_sum(...) to "return .0"
why?

PS I use LDC most time so asking here not in DMD
May 28 2019
parent reply Dennis <dkorpel gmail.com> writes:
On Tuesday, 28 May 2019 at 10:43:38 UTC, KnightMare wrote:

 DMD & LDC change d_with_sum(...) to "return .0"
 why?


Because you are summing an empty array.

```
double d_with_sum(double[] values)  safe pure nothrow
{
     import std.algorithm : sum;
     double[] squares;
     squares[] = values[] * values[];
     return squares.sum;
}
```

`squares` is initialized with length and pointer 0, and the 
values[] * values[] gets truncated to the size of the destination 
memory, so it becomes a no-op.
May 28 2019
parent KnightMare <black80 bk.ru> writes:
 DMD & LDC change d_with_sum(...) to "return .0"
 why?


 Because you are summing an empty array.
 `squares` is initialized with length and pointer 0, and the 
 values[] * values[] gets truncated to the size of the 
 destination memory, so it becomes a no-op.


yep. thx.
C:\content\downloadz\dlang>times2.exe
t1=42 ms, 929 ╬╝s, and 1 hnsec          r=109226661546_74544967680
t2=42 ms and 578 ╬╝s                    r=109226661546_74544967680
t3=333 ms, 539 ╬╝s, and 3 hnsecs        r=109226661546_66672259072
t4=42 ms, 631 ╬╝s, and 9 hnsecs         r=109226661546_74544967680

now I have not small diff but probably double math..
May 28 2019