vicinity 0.6.0

Approximate nearest-neighbor search
Documentation 
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//! Shared utilities for benchmark examples.
//!
//! Loaders for the VEC1/NBR1 binary formats written by
//! `scripts/download_ann_benchmarks.py`.

#![allow(dead_code)]

use std::fs::File;
use std::io::{BufReader, Read};

/// Load vectors from a VEC1 binary file.
///
/// Format: `b"VEC1" + n:u32LE + d:u32LE + n*d f32 values (row-major)`.
///
/// Returns `(vectors, dimension)`.
pub fn load_vectors(path: &str) -> Result<(Vec<Vec<f32>>, usize), Box<dyn std::error::Error>> {
    let file = File::open(path)?;
    let mut reader = BufReader::new(file);

    let mut magic = [0u8; 4];
    reader.read_exact(&mut magic)?;
    assert_eq!(&magic, b"VEC1", "Invalid vector file format");

    let mut header = [0u8; 8];
    reader.read_exact(&mut header)?;
    let n = u32::from_le_bytes([header[0], header[1], header[2], header[3]]) as usize;
    let d = u32::from_le_bytes([header[4], header[5], header[6], header[7]]) as usize;

    let mut data = vec![0u8; n * d * 4];
    reader.read_exact(&mut data)?;

    let vectors: Vec<Vec<f32>> = (0..n)
        .map(|i| {
            (0..d)
                .map(|j| {
                    let offset = (i * d + j) * 4;
                    f32::from_le_bytes([
                        data[offset],
                        data[offset + 1],
                        data[offset + 2],
                        data[offset + 3],
                    ])
                })
                .collect()
        })
        .collect();

    Ok((vectors, d))
}

/// Load ground-truth neighbors from an NBR1 binary file.
///
/// Format: `b"NBR1" + n:u32LE + k:u32LE + n*k i32 values (row-major)`.
///
/// Returns `(neighbors, k)`.
pub fn load_neighbors(path: &str) -> Result<(Vec<Vec<i32>>, usize), Box<dyn std::error::Error>> {
    let file = File::open(path)?;
    let mut reader = BufReader::new(file);

    let mut magic = [0u8; 4];
    reader.read_exact(&mut magic)?;
    assert_eq!(&magic, b"NBR1", "Invalid neighbors file format");

    let mut header = [0u8; 8];
    reader.read_exact(&mut header)?;
    let n = u32::from_le_bytes([header[0], header[1], header[2], header[3]]) as usize;
    let k = u32::from_le_bytes([header[4], header[5], header[6], header[7]]) as usize;

    let mut data = vec![0u8; n * k * 4];
    reader.read_exact(&mut data)?;

    let neighbors: Vec<Vec<i32>> = (0..n)
        .map(|i| {
            (0..k)
                .map(|j| {
                    let offset = (i * k + j) * 4;
                    i32::from_le_bytes([
                        data[offset],
                        data[offset + 1],
                        data[offset + 2],
                        data[offset + 3],
                    ])
                })
                .collect()
        })
        .collect();

    Ok((neighbors, k))
}