forprime in 32bit is 50x slower if p>2^32

[Bill Allombert <Bill.Allombert@math.u-bordeaux1.fr>]

Dear PARI developers,

forprime is very slow in 32bit for large primes:

gettime();my(s);forprime(p=2,6*10^9,s++;if(s%10^7==0,print(p,":",gettime())));s

  ***   last result computed in 2min, 11,909 ms.
give time close to 4700 ms/10^7 primes on 64bit.

On 32bit we get times around 5000ms until we hit 2^32, then:

4222234741:4912
4444120783:172124
4666527007:261320
4889388631:266533
5112733757:270694
5336500537:274085
5560695863:274562
5785258351:278089
? ##
  ***   last result computed in 36min, 7,175 ms.

This is a 50x slowdown. This explains why ellheegner is significantly slower on
32bit.

At least now we get the same number of primes on 32bit and 64bit!

Cheers,
Bill.