Using D1, I have a program that creates tons of float[] ; for performance
reasons, I would like them to be uninitialized.
I've tried replacing

float[] f = new float[x];
by
float[] f = cast(float[])std.gc.malloc(x*4);


Unfortunately I keep running into "Access violation" and sometimes "Array bounds error". I've tried adding

setTypeInfo(typeid(float), f.ptr);
and hasNoPointer(f.ptr);

which didn't work.

However
f[] = float.nan;
solved the problem, but kinda defeats the purpose of using malloc...
What am I doing wrong?

Bear:

> Using D1, I have a program that creates tons of float[] ; for performance
> reasons, I would like them to be uninitialized.
> I've tried replacing
> 
> float[] f = new float[x];
> by
> float[] f = cast(float[])std.gc.malloc(x*4);

Try something like this (untested):

alias float TF;
TF[] f = (cast(TF*)std.gc.malloc(x * TF.sizeof))[0 .. x];

Using x*4 is error-prone. I suggest to wrap that code inside a templated function, where T is the type of the items, to avoid some bugs.

Bye,
bearophile

Am 19.12.2011, 13:04 Uhr, schrieb Bear <joanyleprince@yahoo.fr>:

> Using D1, I have a program that creates tons of float[] ; for performance
> reasons, I would like them to be uninitialized.

std.array.uninitializedArray

On Mon, 19 Dec 2011 07:04:20 -0500, Bear <joanyleprince@yahoo.fr> wrote:

> Using D1, I have a program that creates tons of float[] ; for performance
> reasons, I would like them to be uninitialized.
> I've tried replacing
>
> float[] f = new float[x];
> by
> float[] f = cast(float[])std.gc.malloc(x*4);

this is wrong.  a float[] slice is actually a struct, whereas gc.malloc returns a pointer.

What you have done is cast a pointer into a pointer+length struct, leaving anyones guess as to what the length is set to.  I don't even know why this compiles...

A slice is a pointer + length, and you can slice a pointer to "add a length" to it.  Follow bearophile's suggestion.

> However
> f[] = float.nan;
> solved the problem, but kinda defeats the purpose of using malloc...
> What am I doing wrong?

If this works, it's not doing what you think :)

-Steve

gc.malloc actually returns void[]
Bearophile's suggestion seems to work though, but it doesn't seem to improve
performance for some reason... I guess I'll have to find some other way to make my
prog quicker.

On 2011-12-19 18:24, Bear wrote:
> gc.malloc actually returns void[]
> Bearophile's suggestion seems to work though, but it doesn't seem to improve
> performance for some reason... I guess I'll have to find some other way to make my
> prog quicker.

You can always make the variable uninitialized using "void", don't know if that what is what you're looking for.

float[] f = void;

-- 
/Jacob Carlborg

On Mon, 19 Dec 2011 12:24:18 -0500, Bear <joanyleprince@yahoo.fr> wrote:

> gc.malloc actually returns void[]

http://www.d-programming-language.org/phobos/core_memory.html#malloc

Looks like void* to me...

Or is there another function I'm not aware of?  I think it should be GC.malloc, not gc.malloc, so maybe I'm missing something...

> Bearophile's suggestion seems to work though, but it doesn't seem to improve
> performance for some reason... I guess I'll have to find some other way to make my
> prog quicker.

Actually, an issue with bearophile's suggestion is that it allocates a block marked as containing pointers.  Such a block is bulk-initialized to 0.

Try this:

float[] f = (cast(float*)GC.malloc(x * TF.sizeof, GC.BlkAttr.NO_SCAN))[0 .. x];

This will leave the memory uninitialized.

And depending on the usage, this optimization may or may not make a huge difference.

-Steve

On Mon, 19 Dec 2011 18:52:44 +0100
Jacob Carlborg <doob@me.com> wrote:

> You can always make the variable uninitialized using "void", don't know if that what is what you're looking for.
> 
> float[] f = void;
> 

He is trying to create an array where the elements are not initialized.

On 2011-12-20 01:34, Jesse Phillips wrote:
> On Mon, 19 Dec 2011 18:52:44 +0100
> Jacob Carlborg<doob@me.com>  wrote:
>
>> You can always make the variable uninitialized using "void", don't
>> know if that what is what you're looking for.
>>
>> float[] f = void;
>>
>
> He is trying to create an array where the elements are not initialized.

Ah, I see.

-- 
/Jacob Carlborg

On 19/12/2011 18:11, Steven Schveighoffer wrote:
> On Mon, 19 Dec 2011 12:24:18 -0500, Bear <joanyleprince@yahoo.fr> wrote:
>
>> gc.malloc actually returns void[]
>
> http://www.d-programming-language.org/phobos/core_memory.html#malloc
>
> Looks like void* to me...
>
> Or is there another function I'm not aware of? I think it should be GC.malloc, not
> gc.malloc, so maybe I'm missing something...
<snip>

You are.  That the OP was talking about std.gc.malloc in D1, not the core.memory stuff in D2.

Stewart.