On Saturday, 6 June 2015 at 18:43:08 UTC, Marc Schütz wrote:
_d_arraybounds() always throws an error because that's its
purpose. It's implemented here:
https://github.com/D-Programming-Language/druntime/blob/master/src/core/exception.d#L640
My point was that _d_arraybounds never returns, instead it
throws that Error object.
The compiler inserts the checks for the array length whenever
you access an array element, _except_ if it can either prove
that the array is always long enough (e.g. if its a fixed-size
array), in which case it can leave the check out because it's
unnecessary, or if it can prove that the array is never long
enough, in which case it may already print an error during
compilation.
Okay I think I roughly get it. Another thing that was on my to-do
list just moved up in priority I think.. that thing is learning
everything about the D runtime.
No, the length of the string.
It's roughly the equivalent of this pseudo-code:
extern void _d_arraybounds(void* filename_ptr, size_t
filename_len, size_t line);
void f(void* a_ptr, size_t a_length) {
if(a_length == 0)
goto LBB0_4;
*cast(int*) a_ptr = 0; // line 5
if(a_length <= 1)
goto LBB0_5;
*cast(int*) (a_ptr+4) = 1; // line 6
if(a_length <= 2)
goto LBB0_6;
*cast(int*) (a_ptr+8) = 1; // line 7
return;
LBB0_4:
// (pretend this filename is 55 chars long)
static string __FILE__ = "/path/to/your/source/file.d";
_d_arraybounds(__FILE__.ptr, __FILE__.length, 5 /* line
number */);
LBB0_5:
_d_arraybounds(__FILE__.ptr, __FILE__.length, 6 /* line
number */);
LBB0_6:
_d_arraybounds(__FILE__.ptr, __FILE__.length, 7 /* line
number */);
}
...
Yes, but it is extremely fast. I'm pretty sure accessing memory
at [RSI] and [RSI+4] both take exactly the same time (but can't
find a reference now).
Oh I forgot that the path is part of the filename, so it now
makes a bit more sense on why the names might be so long.
I'm also getting the logic here in a theoretical sense, but in a
practical sense, not quite yet. That'll probably take doing
experiments if anything.
Do you perchance have any links to learning resources for the D
runtime(aside from just the github repository), and also maybe
x86 architecture stuff? (I know intel has some 1000+ page pdf on
their site, but I think that's more for hardware and/or OS
designers..)
Thanks! :)
