On 12/22/2011 10:28 AM, Jacob Carlborg wrote:
On 2011-12-22 08:47, Johannes Pfau wrote:
Hi,
the following code is reduced from a parser generated with Ragel
(http://www.complang.org/ragel/). That's also the reason why it's
using pointers instead of array access, but Ragel guarantees that there
won't be any out-of-bound reads.
AFAIK pointers are supported in CTFE now as long as they're pointing
to an
array and there are no out-of-bounds reads. Still, the following code
fails:
--------------------
ubyte[4] testCTFE()
{
ubyte[4] data;
string input = "8ab3060e2cba4f23b74cb52db3bdfb46";
auto p = input.ptr;
p++; p++;
data[0] = parse!ubyte((p-2)[0 .. 2], 16);
p++; p++;
data[1] = parse!ubyte((p-2)[0 .. 2], 16);
p++; p++;
data[2] = parse!ubyte((p-2)[0 .. 2], 16);
p++; p++;
data[3] = parse!ubyte((p-2)[0 .. 2], 16);
p++; p++;
return data;
}
enum ctfe = testCTFE();
void main()
{
import std.stdio;
writeln(testCTFE()); //[138, 179, 6, 14]
writeln(ctfe); //[138, 138, 138, 138]
}
--------------------
Has this bug already been filed? I could possibly circumvent it by making
ragel use array indexing instead of pointers, but that'd be a performance
issue for runtime code as well.
Why would arrays be slower than pointers? You do know that you can turn
off array bounds checking?
Yes but the length has to be stored and updated, therefore for example
p++ is less machine instructions/memory accesses/register pressure than
arr = arr[1..$].
