How to do cast(ubyte[4])some_uint in D1?
In D2, I can treat a uint as an array of ubytes by doing this: uint num = /+...whatever...+/; ubyte[] = cast(ubyte[4])num; How do I do that in D1? IIRC, D1 requires an explicit slice operator to convert from a static-array to a slice/dynamic-array, so I tried this: ubyte[] = (cast(ubyte[4])num)[]; But I get the error: Error: e2ir: cannot cast num of type uint to type ubyte[4u]
Re: How to do cast(ubyte[4])some_uint in D1?
Nick Sabalausky:
In D2, I can treat a uint as an array of ubytes by doing this:
uint num = /+...whatever...+/;
ubyte[] = cast(ubyte[4])num;
How do I do that in D1?
Using a union is probably the safest way:
union Uint2Ubyte {
uint u;
ubyte[4] b;
}
By the way, this of type conversions is a shady area in D.
Bye,
bearophile
Re: How to do cast(ubyte[4])some_uint in D1?
Nick Sabalausky:
In D2, I can treat a uint as an array of ubytes by doing this:
uint num = /+...whatever...+/;
ubyte[] = cast(ubyte[4])num;
How do I do that in D1?
Using a union is probably the safest way:
union Uint2Ubyte {
uint u;
ubyte[4] b;
}
By the way, this of type conversions is a shady area in D.
Bye,
bearophile
I think it is no so shady after all:
I tested the following code in DMD 2.053:
void main(){
uint a;
ubyte[] b = cast(ubyte[4])a;
}
It gives the same error as in D1.
Timon
Re: How to do cast(ubyte[4])some_uint in D1?
On Thu, 02 Jun 2011 05:35:40 -0400, Nick Sabalausky a@a.a wrote: In D2, I can treat a uint as an array of ubytes by doing this: uint num = /+...whatever...+/; ubyte[] = cast(ubyte[4])num; How do I do that in D1? IIRC, D1 requires an explicit slice operator to convert from a static-array to a slice/dynamic-array, so I tried this: ubyte[] = (cast(ubyte[4])num)[]; But I get the error: Error: e2ir: cannot cast num of type uint to type ubyte[4u] We can learn from C here :) ubyte[] x = (cast(ubyte *)num)[0..4]; Essentially, pointers are *always* castable to one another, and do not go through any translations. Go to pointer-land, then back, and all your casts shall work. It's how C++'s reinterpret_cast works. -Steve
Re: How to do cast(ubyte[4])some_uint in D1?
Timon Gehr timon.g...@gmx.ch wrote in message
news:is7ojo$2ggv$1...@digitalmars.com...
Nick Sabalausky:
In D2, I can treat a uint as an array of ubytes by doing this:
uint num = /+...whatever...+/;
ubyte[] = cast(ubyte[4])num;
How do I do that in D1?
Using a union is probably the safest way:
union Uint2Ubyte {
uint u;
ubyte[4] b;
}
By the way, this of type conversions is a shady area in D.
Bye,
bearophile
I think it is no so shady after all:
I tested the following code in DMD 2.053:
void main(){
uint a;
ubyte[] b = cast(ubyte[4])a;
}
It gives the same error as in D1.
Ok, that's just bizarre. I've just check and verified that you're right. But
I could swear I've done that sort of thing before, and without using the
pointer trick Steve pointed out...
Re: How to do cast(ubyte[4])some_uint in D1?
Nick Sabalausky a@a.a wrote in message
news:is8qu8$1cq3$1...@digitalmars.com...
Timon Gehr timon.g...@gmx.ch wrote in message
news:is7ojo$2ggv$1...@digitalmars.com...
Nick Sabalausky:
In D2, I can treat a uint as an array of ubytes by doing this:
uint num = /+...whatever...+/;
ubyte[] = cast(ubyte[4])num;
How do I do that in D1?
Using a union is probably the safest way:
union Uint2Ubyte {
uint u;
ubyte[4] b;
}
By the way, this of type conversions is a shady area in D.
Bye,
bearophile
I think it is no so shady after all:
I tested the following code in DMD 2.053:
void main(){
uint a;
ubyte[] b = cast(ubyte[4])a;
}
It gives the same error as in D1.
Ok, that's just bizarre. I've just check and verified that you're right.
But I could swear I've done that sort of thing before, and without using
the pointer trick Steve pointed out...
Ah ha! I figured out what I had done before. In D2, casting a struct to a
same-sized static array works fine:
struct Foo {uint f;}
void main(){
Foo a;
ubyte[] b = cast(ubyte[4])a;
}
Verified on DMD 2.053, 2.052 and 2.051. It doesn't work on D1 though (at
least not 1.066 with tango trunk). But I'll try Steve's pointer trick for
that.
As a nice touch, it fails in D2 if you change the ubyte[4] to ubyte[5].
Using ubyte[3] is prohibited, too, even though I would think that should
be ok. But that's probably not a real big deal.
But...it seems strange that casting a primitive to a static array would be
prohibited if it's perfectly kosher when the primitive is in a struct. So
I've filed a bug report on that:
Can't cast primitive to same-sized static array
http://d.puremagic.com/issues/show_bug.cgi?id=6092
