• ag0aep6g (17/17) Feb 26 2023 ```d
• H. S. Teoh (5/23) Feb 26 2023 LDC and GDC both work fine.
• claptrap (20/37) Feb 26 2023 Looking via godbolt
• user1234 (4/7) Feb 27 2023 I bet it's because of integral promotion. Once an element loaded

ag0aep6g <anonymous example.com> writes:

```d
void main()
{
     ubyte[] a = [1];
     foreach (x; a)
     {
         ubyte v = x >= 1 ? 255 : 0;
         assert(v == 255); /* fails; should pass */
     }
}
```

Astonishing.

Filed as [issue 
23743](https://issues.dlang.org/show_bug.cgi?id=23743).

Reminds me of [issue 
18315](https://issues.dlang.org/show_bug.cgi?id=18315) ("wrong 
code for `i > 0`") which was similarly ridiculous.

"H. S. Teoh" <hsteoh qfbox.info> writes:

On Sun, Feb 26, 2023 at 12:49:25PM +0000, ag0aep6g via Digitalmars-d wrote:
 ```d
 void main()
 {
     ubyte[] a = [1];
     foreach (x; a)
     {
         ubyte v = x >= 1 ? 255 : 0;
         assert(v == 255); /* fails; should pass */
     }
 }
 ```
 
 Astonishing.
 
 Filed as [issue 23743](https://issues.dlang.org/show_bug.cgi?id=23743).
 
 Reminds me of [issue 18315](https://issues.dlang.org/show_bug.cgi?id=18315)
 ("wrong code for `i > 0`") which was similarly ridiculous.

LDC and GDC both work fine.


T

-- 
Trying to define yourself is like trying to bite your own teeth. -- Alan Watts

claptrap <clap trap.com> writes:

On Sunday, 26 February 2023 at 12:49:25 UTC, ag0aep6g wrote:
 ```d
 void main()
 {
     ubyte[] a = [1];
     foreach (x; a)
     {
         ubyte v = x >= 1 ? 255 : 0;
         assert(v == 255); /* fails; should pass */
     }
 }
 ```

 Astonishing.

 Filed as [issue 
 23743](https://issues.dlang.org/show_bug.cgi?id=23743).

 Reminds me of [issue 
 18315](https://issues.dlang.org/show_bug.cgi?id=18315) ("wrong 
 code for `i > 0`") which was similarly ridiculous.

Looking via godbolt

this line : ubyte v = x >= 1 ? 255 : 0; -->

xor     EBX,EBX       // 1 foreach index counter set to zero
mov     RAX,-8[RBP]   // 2 load address of array litteral
cmp     [RAX][RBX],1  // 3 compare array element with 1
sbb     R12D,R12D     // 4 set R12D to zero, or FFFFFFFF if 
borrow flag set
not     R12B          // 5 invert the bits
mov     EDI,R12D      // lets pretent the result is 32 bits now?

I think the problem is that (4) does 32 bits 0 or FFFFFFF, and 
that (5) inverts only the lower 8 bits. IIRC writing to lower 32 
bits register zeros the upper 64 bits, but writing to 16 or 8 
bits doesn't affect the upper bits at all. I mean it would have 
broken a ton of existing code if they done that.

So i dont know if the error is that the NOT should be 32 bits, or 
that the following code should be using R12B and not thinking its 
a 32 bit value.

Even the (3) compare looks iffy, its an array of bytes but looks 
like the compare is 32 bit?

user1234 <user1234 12.de> writes:

On Sunday, 26 February 2023 at 20:47:47 UTC, claptrap wrote:
 [...]
 Even the (3) compare looks iffy, its an array of bytes but 
 looks like the compare is 32 bit?

I bet it's because of integral promotion. Once an element loaded 
it's promoted to int, i.e there should be a "signed extension". I 
see ldc does it in the form of a "movzx" instruction.