LR-EDIT-DETAIL-DENOISE: address installation and model-policy review

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crates/denoise-core/src/hash.rs

@@ -0,0 +1,46 @@
+//! SHA-256 of a model file, streamed (a model can be hundreds of megabytes).
+
+use std::io::{self, Read};
+use std::path::Path;
+
+use sha2::{Digest, Sha256};
+
+/// Lowercase hex SHA-256 of everything `r` yields.
+pub fn sha256_reader<R: Read>(mut r: R) -> io::Result<String> {
+    let mut h = Sha256::new();
+    let mut buf = vec![0u8; 1 << 20];
+    loop {
+        let n = r.read(&mut buf)?;
+        if n == 0 {
+            break;
+        }
+        h.update(buf.get(..n).unwrap_or(&[]));
+    }
+    Ok(hex(&h.finalize()))
+}
+
+/// Lowercase hex SHA-256 of a file.
+pub fn sha256_file(path: &Path) -> io::Result<String> {
+    sha256_reader(io::BufReader::new(std::fs::File::open(path)?))
+}
+
+/// Lowercase hex SHA-256 of `bytes`.
+pub fn sha256_hex(bytes: &[u8]) -> String {
+    hex(&Sha256::digest(bytes))
+}
+
+fn hex(bytes: &[u8]) -> String {
+    bytes.iter().map(|b| format!("{b:02x}")).collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn known_digests() {
+        assert_eq!(sha256_hex(b""), "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855");
+        assert_eq!(sha256_hex(b"abc"), "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad");
+        assert_eq!(sha256_reader(&b"abc"[..]).unwrap(), sha256_hex(b"abc"));
+    }
+}