How can I write compile-time (pure) BigInt computations?

[Timon Gehr]

On 10/25/2011 02:37 PM, Gor Gyolchanyan wrote:
> That's because N is not a compile-time value. Initializing global
> variable is allowed only with compile-time values, but the variable
> themselves are run-time values.
> This could probably be fixed, since the initial values of global
> variables are always known.
>
> Anyway, if the value of N (and probable X too) is not subject to
> modification, you should make then either immutable or, better yet,
> enum.
> This way they WILL be compile-time values and you won't get that error.
>
> On Tue, Oct 25, 2011 at 4:31 PM, Chris Dew<cmsdew at gmail.com>  wrote:
>> Stuck again, looks like BigInt doesn't work with CTFE for other reasons...
>>
>> Is there a way to create BigInts at compile time (I've also tried from
>> a string)?  Or is it back to C code generation in Python :-(
>>
>> Thanks anyway,
>>
>> Chris.
>>
>>
>> ./gcd.d(11): Error: static variable N cannot be read at compile time
>> ./gcd.d(11): Error: cannot evaluate gcd((BigInt __ctmp1335;
>>   , __ctmp1335).this(48),N) at compile time
>> Failed: dmd  -v -o- './gcd.d' -I'.'>./gcd.d.deps
>>
>>
>>
>> import std.stdio;
>> import std.bigint;
>>
>> T gcd(T)(T a, T b) {
>>   if (b == 0) return a;
>>   return gcd(b, a % b);
>> }
>>
>>
>> BigInt N = cast(BigInt)1000000000L;
>> BigInt X = gcd(cast(BigInt)48, N);
>>
>> int main() {
>>   writefln("%s", X);
>>   return 0;
>> }
>>

BigInt operates using hand-written assembly, if available for the target 
architecture. inline asm cannot be used in CTFE. CTFE for BigInt would 
specifically have to be supported by a patch to Phobos.