Skip to content

Optimized unxorshift #82

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 1 commit into
base: master
Choose a base branch
from
Open

Optimized unxorshift #82

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
20 changes: 5 additions & 15 deletions include/pcg_extras.hpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -263,21 +263,11 @@ inline std::istream& operator>>(std::istream& in, uint8_t& value)
template <typename itype>
inline itype unxorshift(itype x, bitcount_t bits, bitcount_t shift)
{
if (2*shift >= bits) {
return x ^ (x >> shift);
}
itype lowmask1 = (itype(1U) << (bits - shift*2)) - 1;
itype highmask1 = ~lowmask1;
itype top1 = x;
itype bottom1 = x & lowmask1;
top1 ^= top1 >> shift;
top1 &= highmask1;
x = top1 | bottom1;
itype lowmask2 = (itype(1U) << (bits - shift)) - 1;
itype bottom2 = x & lowmask2;
bottom2 = unxorshift(bottom2, bits - shift, shift);
bottom2 &= lowmask1;
return top1 | bottom2;
do {
x ^= x >> shift;
shift *= 2u;
} while(shift < bits);
return x;
}

/*
Expand Down