Fix hashing overflow issues (#86)

noxfile.py

@@ -38,7 +38,18 @@ def tests(session):
     """
     Run the test suite with a corresponding Python version.
     """
-    session.install("-r", REQUIREMENTS["tests"])
+    # Really we want --profile=test here (for
+    # https://github.com/crate-py/rpds/pull/87#issuecomment-2291409297)
+    # but it produces strange symbol errors saying:
+    #   dynamic module does not define module export function (PyInit_rpds)
+    # so OK, dev it is.
+    session.install(
+        "--config-settings",
+        "build-args=--profile=dev",
+        "--no-cache",
+        "-r",
+        REQUIREMENTS["tests"],
+    )
 
     if session.posargs and session.posargs[0] == "coverage":
         if len(session.posargs) > 1 and session.posargs[1] == "github":

src/lib.rs

@@ -10,7 +10,7 @@ use std::collections::hash_map::DefaultHasher;
 use std::hash::{Hash, Hasher};
 
 fn hash_shuffle_bits(h: usize) -> usize {
-    ((h ^ 89869747) ^ (h << 16)) * 3644798167
+    ((h ^ 89869747) ^ (h << 16)).wrapping_mul(3644798167)
 }
 
 #[derive(Debug)]
@@ -217,11 +217,11 @@ impl HashTrieMapPy {
             })?;
 
         // factor in the number of entries in the collection
-        hash_val ^= (self.inner.size() + 1) * 1927868237;
+        hash_val ^= self.inner.size().wrapping_add(1).wrapping_mul(1927868237);
 
         // dispense patterns in the hash value
         hash_val ^= (hash_val >> 11) ^ (hash_val >> 25);
-        hash_val = hash_val * 69069 + 907133923;
+        hash_val = hash_val.wrapping_mul(69069).wrapping_add(907133923);
 
         Ok(hash_val as isize)
     }
@@ -833,11 +833,11 @@ impl HashTrieSetPy {
             .fold(0, |acc: usize, x: usize| acc ^ hash_shuffle_bits(x));
 
         // factor in the number of entries in the collection
-        hash_val ^= (self.inner.size() + 1) * 1927868237;
+        hash_val ^= self.inner.size().wrapping_add(1).wrapping_mul(1927868237);
 
         // dispense patterns in the hash value
         hash_val ^= (hash_val >> 11) ^ (hash_val >> 25);
-        hash_val = hash_val * 69069 + 907133923;
+        hash_val = hash_val.wrapping_mul(69069).wrapping_add(907133923);
 
         Ok(hash_val as isize)
     }