Fixes integer handling in Decimal::to_f64 by expanding range (#443)

paupino · Nov 25, 2021 · 2f2d0fb · 2f2d0fb
1 parent 9b6a1ce
commit 2f2d0fb
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Showing 2 changed files with 10 additions and 5 deletions.
diff --git a/src/decimal.rs b/src/decimal.rs
@@ -2090,7 +2090,10 @@ impl ToPrimitive for Decimal {
 
     fn to_f64(&self) -> Option<f64> {
         if self.scale() == 0 {
-            let integer = self.to_i64();
+            // If scale is zero, we are storing a 96-bit integer value, that would
+            // always fit into i128, which in turn is always representable as f64,
+            // albeit with loss of precision for values outside of -2^53..2^53 range.
+            let integer = self.to_i128();
             integer.map(|i| i as f64)
         } else {
             let sign: f64 = if self.is_sign_negative() { -1.0 } else { 1.0 };

diff --git a/tests/decimal_tests.rs b/tests/decimal_tests.rs
@@ -2570,9 +2570,10 @@ fn it_converts_to_f64() {
             "2.1234567890123456789012345678",
             Some(2.1234567890123456789012345678_f64),
         ),
+        ("21234567890123456789012345678", Some(21234567890123458000000000000_f64)),
         (
-            "21234567890123456789012345678",
-            None, // Cannot be represented in an f64
+            "-21234567890123456789012345678",
+            Some(-21234567890123458000000000000_f64),
         ),
         ("1.59283191", Some(1.59283191_f64)),
         ("2.2238", Some(2.2238_f64)),
@@ -2600,9 +2601,10 @@ fn it_converts_to_f64_try() {
             "2.1234567890123456789012345678",
             Some(2.1234567890123456789012345678_f64),
         ),
+        ("21234567890123456789012345678", Some(21234567890123458000000000000_f64)),
         (
-            "21234567890123456789012345678",
-            None, // Cannot be represented in an f64
+            "-21234567890123456789012345678",
+            Some(-21234567890123458000000000000_f64),
         ),
         ("1.59283191", Some(1.59283191_f64)),
     ];