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use num_traits::float::FloatCore;
use std::cmp::Ordering;
#[allow(dead_code)] // We don't use this currently, but migth in the future.
pub fn z_cmp_ints(lhs: &[usize], rhs: &[usize]) -> Ordering {
assert_eq!(
lhs.len(),
rhs.len(),
"Cannot compare array with different lengths."
);
let mut msd = 0;
for dim in 1..rhs.len() {
if less_msb(lhs[msd] ^ rhs[msd], lhs[dim] ^ rhs[dim]) {
msd = dim;
}
}
lhs[msd].cmp(&rhs[msd])
}
fn less_msb(x: usize, y: usize) -> bool {
x < y && x < (x ^ y)
}
// Fast construction of k-Nearest Neighbor Graphs for Point Clouds
// Michael Connor, Piyush Kumar
// Algorithm 1
//
// http://compgeom.com/~piyush/papers/tvcg_stann.pdf
pub fn z_cmp_floats(p1: &[f32], p2: &[f32]) -> Option<Ordering> {
assert_eq!(
p1.len(),
p2.len(),
"Cannot compare array with different lengths."
);
let mut x = 0;
let mut dim = 0;
for j in 0..p1.len() {
let y = xor_msb_float(p1[j], p2[j]);
if x < y {
x = y;
dim = j;
}
}
p1[dim].partial_cmp(&p2[dim])
}
fn xor_msb_float(fa: f32, fb: f32) -> i16 {
let (mantissa1, exponent1, _sign1) = fa.integer_decode();
let (mantissa2, exponent2, _sign2) = fb.integer_decode();
let x = exponent1; // To keep the same notation as the paper.
let y = exponent2; // To keep the same notation as the paper.
if x == y {
let z = msdb(mantissa1, mantissa2);
x - z
} else if y < x {
x
} else {
y
}
}
fn msdb(x: u64, y: u64) -> i16 {
64i16 - (x ^ y).leading_zeros() as i16
}
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