cosmopolitan/libc/bits/morton.c

38 lines
2.4 KiB
C

/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney │
│ │
│ This program is free software; you can redistribute it and/or modify │
│ it under the terms of the GNU General Public License as published by │
│ the Free Software Foundation; version 2 of the License. │
│ │
│ This program is distributed in the hope that it will be useful, but │
│ WITHOUT ANY WARRANTY; without even the implied warranty of │
│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU │
│ General Public License for more details. │
│ │
│ You should have received a copy of the GNU General Public License │
│ along with this program; if not, write to the Free Software │
│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
│ 02110-1301 USA │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/bits/morton.h"
/**
* Interleaves bits.
*/
unsigned long(morton)(unsigned long y, unsigned long x) {
x = (x | x << 020) & 0x0000FFFF0000FFFF;
x = (x | x << 010) & 0x00FF00FF00FF00FF;
x = (x | x << 004) & 0x0F0F0F0F0F0F0F0F;
x = (x | x << 002) & 0x3333333333333333;
x = (x | x << 001) & 0x5555555555555555;
y = (y | y << 020) & 0x0000FFFF0000FFFF;
y = (y | y << 010) & 0x00FF00FF00FF00FF;
y = (y | y << 004) & 0x0F0F0F0F0F0F0F0F;
y = (y | y << 002) & 0x3333333333333333;
y = (y | y << 001) & 0x5555555555555555;
return x | y << 1;
}