78 lines
1.6 KiB
Rust
78 lines
1.6 KiB
Rust
#![allow(dead_code)]
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const N: u32 = 1 << 16;
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// Utility function used by the functions below.
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fn hil_rot(n: u32, rx: u32, ry: u32, x: &mut u32, y: &mut u32) {
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use std::mem;
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if ry == 0 {
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if rx == 1 {
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*x = (n - 1).wrapping_sub(*x);
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*y = (n - 1).wrapping_sub(*y);
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}
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mem::swap(x, y);
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}
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}
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/// Convert (x,y) to hilbert curve index.
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///
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/// x: The x coordinate. Must be a positive integer no greater than 2^16-1.
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/// y: The y coordinate. Must be a positive integer no greater than 2^16-1.
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///
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/// Returns the hilbert curve index corresponding to the (x,y) coordinates given.
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pub fn xy2d(x: u32, y: u32) -> u32 {
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assert!(x < N);
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assert!(y < N);
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let (mut x, mut y) = (x, y);
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let mut d = 0;
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let mut s = N >> 1;
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while s > 0 {
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let rx = if (x & s) > 0 { 1 } else { 0 };
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let ry = if (y & s) > 0 { 1 } else { 0 };
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d += s * s * ((3 * rx) ^ ry);
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hil_rot(s, rx, ry, &mut x, &mut y);
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s >>= 1
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}
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d
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}
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/// Convert hilbert curve index to (x,y).
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///
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/// d: The hilbert curve index.
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///
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/// Returns the (x, y) coords at the given index.
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pub fn d2xy(d: u32) -> (u32, u32) {
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let (mut x, mut y) = (0, 0);
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let mut s = 1;
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let mut t = d;
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while s < N {
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let rx = 1 & (t >> 1);
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let ry = 1 & (t ^ rx);
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hil_rot(s, rx, ry, &mut x, &mut y);
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x += s * rx;
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y += s * ry;
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t >>= 2;
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s <<= 1;
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}
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(x, y)
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn reversible() {
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let d = 54;
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let (x, y) = d2xy(d);
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let d2 = xy2d(x, y);
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assert_eq!(d, d2);
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}
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}
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