Re: Checking if a structs .init value is zero bits only
On Wednesday, 28 March 2018 at 01:39:40 UTC, Seb wrote: Have a look at: https://github.com/dlang/phobos/pull/6024 (review/feedbackon this PR is welcome!) Exactly what I wanted. Thanks! In use here https://github.com/nordlow/phobos-next/blob/41b9e0dcfbb4eed6b2ee52d0465425556f14c00f/src/open_hashmap_or_hashset.d#L242
Re: Checking if a structs .init value is zero bits only
On Wednesday, 28 March 2018 at 00:50:31 UTC, Ali Çehreli wrote:
On 03/27/2018 05:15 PM, Per Nordlöw wrote:
Is there a way to check if a struct `S` can be initialized
using zero bits only, so that we can allocate and initialize
an array of `S` in one go using `calloc`? If not, what should
such a trait look like?
The following idea should work. One question that I'm not
certain about is whether padding bytes inside .init can ever be
non-zero in D. I assumed they are always zero. If not, the same
idea must be applied recursively to individual members.
bool allZeros(T)() {
// Yes, this can be implemented as a range algorithm. :)
T t;
foreach (b; (cast(ubyte*))[0..T.sizeof]) {
if (b) {
return false;
}
}
return true;
}
Yes, of course, thanks.
But my goal is (always) to have it done at compile-time.
Re: Checking if a structs .init value is zero bits only
On Wednesday, 28 March 2018 at 00:15:34 UTC, Per Nordlöw wrote: Is there a way to check if a struct `S` can be initialized using zero bits only, so that we can allocate and initialize an array of `S` in one go using `calloc`? If not, what should such a trait look like? Have a look at: https://github.com/dlang/phobos/pull/6024 (review/feedbackon this PR is welcome!)
Re: Checking if a structs .init value is zero bits only
On 03/27/2018 05:15 PM, Per Nordlöw wrote:
Is there a way to check if a struct `S` can be initialized using zero
bits only, so that we can allocate and initialize an array of `S` in one
go using `calloc`? If not, what should such a trait look like?
The following idea should work. One question that I'm not certain about
is whether padding bytes inside .init can ever be non-zero in D. I
assumed they are always zero. If not, the same idea must be applied
recursively to individual members.
bool allZeros(T)() {
// Yes, this can be implemented as a range algorithm. :)
T t;
foreach (b; (cast(ubyte*))[0..T.sizeof]) {
if (b) {
return false;
}
}
return true;
}
unittest {
static struct A {
int i;
long l;
}
static struct B {
double d;
}
assert(allZeros!A);
assert(!allZeros!B);
}
void main() {
}
Ali
Checking if a structs .init value is zero bits only
Is there a way to check if a struct `S` can be initialized using zero bits only, so that we can allocate and initialize an array of `S` in one go using `calloc`? If not, what should such a trait look like?
