Fix Decimal::to_i64 for I64::MIN (#496)

Co-authored-by: Paul Mason <paul@paulmason.me> Co-authored-by: Arthur Silva <arthurprs@gmail.com>
paupino · Mar 19, 2022 · 2de2a6d · 2de2a6d
1 parent 168fa67
commit 2de2a6d
Show file tree

Hide file tree

Showing 2 changed files with 35 additions and 13 deletions.
diff --git a/src/decimal.rs b/src/decimal.rs
@@ -2203,15 +2203,26 @@ fn base2_to_decimal(
 impl ToPrimitive for Decimal {
     fn to_i64(&self) -> Option<i64> {
         let d = self.trunc();
-        // Quick overflow check
-        if d.hi != 0 || (d.mid & 0x8000_0000) > 0 {
+        // If it is in the hi bit then it is a clear overflow.
+        if d.hi != 0 {
             // Overflow
             return None;
         }
+        let negative = self.is_sign_negative();
+
+        // A bit more convoluted in terms of checking when it comes to the hi bit due to twos-complement
+        if d.mid & 0x8000_0000 > 0 {
+            if negative && d.mid == 0x8000_0000 && d.lo == 0 {
+                // We do this because below we try to convert the i64 to a positive first - of which
+                // doesn't fit into an i64.
+                return Some(i64::MIN);
+            }
+            return None;
+        }
 
         let raw: i64 = (i64::from(d.mid) << 32) | i64::from(d.lo);
-        if self.is_sign_negative() {
-            Some(-raw)
+        if negative {
+            Some(raw.neg())
         } else {
             Some(raw)
         }

diff --git a/tests/decimal_tests.rs b/tests/decimal_tests.rs
@@ -2633,15 +2633,26 @@ fn it_converts_to_f64_try() {
 
 #[test]
 fn it_converts_to_i64() {
-    assert_eq!(5i64, Decimal::from_str("5").unwrap().to_i64().unwrap());
-    assert_eq!(-5i64, Decimal::from_str("-5").unwrap().to_i64().unwrap());
-    assert_eq!(5i64, Decimal::from_str("5.12345").unwrap().to_i64().unwrap());
-    assert_eq!(-5i64, Decimal::from_str("-5.12345").unwrap().to_i64().unwrap());
-    assert_eq!(
-        0x7FFF_FFFF_FFFF_FFFF,
-        Decimal::from_str("9223372036854775807").unwrap().to_i64().unwrap()
-    );
-    assert_eq!(None, Decimal::from_str("92233720368547758089").unwrap().to_i64());
+    let tests = [
+        ("5", Some(5_i64)),
+        ("-5", Some(-5_i64)),
+        ("5.12345", Some(5_i64)),
+        ("-5.12345", Some(-5_i64)),
+        ("-9223372036854775808", Some(-9223372036854775808_i64)),
+        ("-9223372036854775808", Some(i64::MIN)),
+        ("9223372036854775807", Some(9223372036854775807_i64)),
+        ("9223372036854775807", Some(i64::MAX)),
+        ("-9223372036854775809", None), // i64::MIN - 1
+        ("9223372036854775808", None),  // i64::MAX + 1
+        // Clear overflows in hi bit
+        ("-92233720368547758089", None),
+        ("92233720368547758088", None),
+    ];
+    for (input, expected) in tests {
+        let input = Decimal::from_str(input).unwrap();
+        let actual = input.to_i64();
+        assert_eq!(expected, actual, "Input: {}", input);
+    }
 }
 
 #[test]