fix overflow bug where keys are close to overflow (fixes #16)

src/setu32.rs

@@ -1717,7 +1717,10 @@ fn p_poverty(k: u32, idx: usize, n: usize) -> usize {
 fn p_insert(k: u32, a: &mut [u32], offset: u32) -> usize {
     let n = a.len();
     for pov in 0..n {
-        let ii = ((k + pov as u32) % n as u32) as usize;
+        // The cast to u64 below avoids overflow issues when `k` is close
+        // to `u32::MAX`.  It should cost nothing on 64-bit machines, and
+        // shouldn't be much worse than an extra `%` on 32-bit machines.
+        let ii = ((k as u64 + pov as u64) % n as u64) as usize;
         let ki = a[ii] >> offset;
         let pov_ki = p_poverty(ki, ii, n);
         if a[ii] == 0 || ki == k {
@@ -1814,7 +1817,10 @@ impl LookedUp {
 fn p_lookfor(k: u32, a: &[u32], offset: u32) -> LookedUp {
     let n = a.len();
     for pov in 0..n {
-        let ii = ((k + pov as u32) % n as u32) as usize;
+        // The cast to u64 below avoids overflow issues when `k` is close
+        // to `u32::MAX`.  It should cost nothing on 64-bit machines, and
+        // shouldn't be much worse than an extra `%` on 32-bit machines.
+        let ii = ((k as u64 + pov as u64) % n as u64) as usize;
         // println!("looking in spot ii = {} with pov={}", ii, pov);
         if a[ii] == 0 {
             // println!("got empty spot at {} for key {}", ii, k);
@@ -1843,7 +1849,10 @@ fn test_lookfor() {
 fn p_remove(k: u32, a: &mut [u32], offset: u32) -> bool {
     let n = a.len();
     for i in 0..n {
-        let ii = ((k + i as u32) % n as u32) as usize;
+        // The cast to u64 below avoids overflow issues when `k` is close
+        // to `u32::MAX`.  It should cost nothing on 64-bit machines, and
+        // shouldn't be much worse than an extra `%` on 32-bit machines.
+        let ii = ((k as u64 + i as u64) % n as u64) as usize;
         // println!("    looking to remove at distance {} slot {}", i, ii);
         if a[ii] == 0 {
             return false;

src/setu32b.rs

@@ -1162,7 +1162,7 @@ fn p_insert_better(k: u32, a: &mut [(u32,u32)]) -> Inserted {
     let n = a.len();
     let poverty_limit = n;
     for pov in 0..poverty_limit {
-        let ii = ((k + pov as u32) % n as u32) as usize;
+        let ii = ((k as u64 + pov as u64) % n as u64) as usize;
         let ki = a[ii].0;
         let pov_ki = p_poverty(ki, ii, n);
         if a[ii] == (0,0) {
@@ -1261,7 +1261,7 @@ impl LookedUp {
 fn p_lookfor(k: u32, a: &[(u32,u32)]) -> LookedUp {
     let n = a.len();
     for pov in 0..n {
-        let ii = ((k + pov as u32) % n as u32) as usize;
+        let ii = ((k as u64 + pov as u64) % n as u64) as usize;
         if a[ii] == (0,0) {
             // println!("got empty spot at {} for key {}", ii, k);
             return LookedUp::EmptySpot(ii);
@@ -1289,7 +1289,7 @@ fn test_lookfor() {
 fn p_remove(k: u32, a: &mut [(u32,u32)]) -> bool {
     let n = a.len();
     for i in 0..n {
-        let ii = ((k + i as u32) % n as u32) as usize;
+        let ii = ((k as u64 + i as u64) % n as u64) as usize;
         // println!("    looking to remove at distance {} slot {}", i, ii);
         if a[ii] == (0,0) {
             return false;

src/setu64.rs

@@ -1723,7 +1723,7 @@ fn p_poverty(k: u64, idx: usize, n: usize) -> usize {
 fn p_insert(k: u64, a: &mut [u64], offset: u64) -> usize {
     let n = a.len();
     for pov in 0..n {
-        let ii = ((k + pov as u64) % n as u64) as usize;
+        let ii = (((k % n as u64) + pov as u64) % n as u64) as usize;
         let ki = a[ii] >> offset;
         let pov_ki = p_poverty(ki, ii, n);
         if a[ii] == 0 || ki == k {
@@ -1820,7 +1820,7 @@ impl LookedUp {
 fn p_lookfor(k: u64, a: &[u64], offset: u64) -> LookedUp {
     let n = a.len();
     for pov in 0..n {
-        let ii = ((k + pov as u64) % n as u64) as usize;
+        let ii = (((k % n as u64) + pov as u64) % n as u64) as usize;
         // println!("looking in spot ii = {} with pov={}", ii, pov);
         if a[ii] == 0 {
             // println!("got empty spot at {} for key {}", ii, k);
@@ -1849,7 +1849,7 @@ fn test_lookfor() {
 fn p_remove(k: u64, a: &mut [u64], offset: u64) -> bool {
     let n = a.len();
     for i in 0..n {
-        let ii = ((k + i as u64) % n as u64) as usize;
+        let ii = (((k % n as u64) + i as u64) % n as u64) as usize;
         // println!("    looking to remove at distance {} slot {}", i, ii);
         if a[ii] == 0 {
             return false;

tests/add-with-overflow-issue-16.rs

@@ -0,0 +1,20 @@
+use tinyset::Set64;
+
+#[test]
+fn issue_16() {
+    let mut a: Set64<u64> = Set64::new();
+    let mut b: Set64<u64> = Set64::new();
+    a.insert(u64::MAX);
+    a.insert(8589934592);
+    a.insert(8589934593);
+    a.insert(17179869184);
+    a.insert(17179869185);
+    a.insert(12884901889);
+    b.insert(17179869187);
+    b.insert(17179869188);
+    b.insert(12884901889);
+    b.insert(12884901890);
+    b.insert(12884901891);
+    b.insert(12884901892);
+    let _c = &a - &b;
+}