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#![crate_name = "basiccms"] #![crate_type = "lib"] extern crate rand; use std::hash::{ SipHasher, Hasher, Hash }; pub struct Sketch { width : usize, depth : usize, buckets: Vec<Vec<u64>>, hash_offsets: Vec<u64> } impl Sketch { pub fn add<T: IntoSketch>(&mut self, val: T) -> &Sketch { for row in 0..self.depth { let key = self.index(&val, row); let value = self.buckets[row][key]; self.buckets[row][key] = value + 1; } self } pub fn point<T: IntoSketch>(&mut self, val: T) -> u64 { let mut counts = Vec::with_capacity(self.depth); for row in 0..self.depth { let key = self.index(&val, row); let value = self.buckets[row][key]; counts.push(value); } *counts.iter().min().unwrap() } pub fn new(epsilon: f64, delta: f64) -> Sketch { if epsilon < 0.0 { panic!("CMS: epsilon must be positive"); } if delta < 0.0 || delta > 1.0 { panic!("CMS: delta must be in (0.0, 1.0)"); } let width = (std::f64::consts::E / epsilon).ceil() as usize; let depth = (1.0 / delta).ln().ceil() as usize; let hash_offsets = Sketch::make_hash_offsets(depth); Sketch { width: width, depth: depth, buckets: vec![vec![0; width]; depth], hash_offsets: hash_offsets } } fn index<T: IntoSketch>(&mut self, val: &T, row: usize) -> usize { let sketched = val.asu64(); let offset = self.hash_offsets[row]; let hashed = sketched.wrapping_mul(offset); (hashed % (self.width as u64)) as usize } fn make_hash_offsets(depth: usize) -> Vec<u64> { let mut hashers: Vec<u64> = Vec::with_capacity(depth); for _ in 0..depth { hashers.push(rand::random::<u64>()); } hashers } } fn elementwise_sum(left: &Vec<Vec<u64>>, right: &Vec<Vec<u64>>) -> Vec<Vec<u64>> { left.iter() .zip(right.iter()) .map(|(l, r)| l.iter().zip(r.iter()).map(|(x, y)| x + y).collect()) .collect() } impl<'a> std::ops::Add<&'a Sketch> for &'a Sketch { type Output = Sketch; fn add(self, other: &'a Sketch) -> Sketch { assert_eq!(self.width, other.width); assert_eq!(self.depth, other.depth); assert_eq!(self.hash_offsets, other.hash_offsets); Sketch { width: self.width, depth: self.depth, hash_offsets: self.hash_offsets.clone(), buckets: elementwise_sum(&self.buckets, &other.buckets) } } } impl std::clone::Clone for Sketch { fn clone(&self) -> Sketch { Sketch { width: self.width, depth: self.depth, hash_offsets: self.hash_offsets.clone(), buckets: self.buckets.clone() } } } pub trait IntoSketch { fn asu64(&self) -> u64; } impl IntoSketch for u64 { fn asu64(&self) -> u64 { *self } } impl IntoSketch for String { fn asu64(&self) -> u64 { let mut hasher = SipHasher::new(); self.hash(&mut hasher); hasher.finish() } } impl<'a> IntoSketch for &'a str { fn asu64(&self) -> u64 { let mut hasher = SipHasher::new(); self.hash(&mut hasher); hasher.finish() } }