50g: an interesting RAND anomaly

[cyrille de brébisson]

Hello,

Here is the random generator source code. This should give you ALL the info you may want (including the reason why you see what you are seeing).
HP_Real fRand(uint64_t *Seed)
{
if (*Seed==0LL) *Seed= BaseSeed;
HP_Real r; r.M= 0LL;
uint64_t c= 0x2851130928467LL;
for (int i= 13; --i>=0; i--)
{
r.M= dcb_muladd(r.M, *Seed, ((uint32_t)c)&15); // r.M= r.M+seed*low nibble of c
*Seed<<= 4;
c>>= 4;
}
*Seed= r.M&0x0fffffffffffffffLL; // update seed for next time
r.e= -1; r.s= SignPos; // result's exponent is -1 and sign is pos
while((r.M&0xf00000000000000LL)==0) { r.M <<= 4; r.e--; } // Normalize real
r.M &= 0x0ffffffffffff000LL; // round to 12 significant digits
return r;
}

Cheers,
Cyrille