Fixes #3500

src/Fable.Cli/CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+### Fixed
+
+* [JS/TS] Fixed BigInt.ToDecimal with negative values (#3500) (by @ncave)
+
 ## 4.19.1 - 2024-06-13
 
 ### Fixed

src/fable-library-ts/BigInt.ts

@@ -148,10 +148,11 @@ export function toFloat32(x: bigint): float32 { return Number(x); }
 export function toFloat64(x: bigint): float64 { return Number(x); }
 
 export function toDecimal(x: bigint): decimal {
-    const low = Number(BigInt.asUintN(32, x))
-    const mid = Number(BigInt.asUintN(32, x >> 32n))
-    const high = Number(BigInt.asUintN(32, x >> 64n))
     const isNegative = x < zero;
+    const bits = abs(x);
+    const low = Number(BigInt.asUintN(32, bits));
+    const mid = Number(BigInt.asUintN(32, bits >> 32n));
+    const high = Number(BigInt.asUintN(32, bits >> 64n));
     const scale = 0;
     return fromParts(low, mid, high, isNegative, scale)
 }

tests/Js/Main/ConvertTests.fs

@@ -1090,6 +1090,14 @@ let tests =
         let value = 1.0m
         decimal (bigint value) |> equal value
 
+    testCase "BigInt ToDecimal with Decimal.MinValue works" <| fun () ->
+        let value = Decimal.MinValue
+        decimal (bigint value) |> equal value
+
+    testCase "BigInt ToDecimal with Decimal.MaxValue works" <| fun () ->
+        let value = Decimal.MaxValue
+        decimal (bigint value) |> equal value
+
     testCase "BigInt ToString works" <| fun () ->
         let value = 1234567890
         string (bigint value) |> equal "1234567890"

tests/Python/TestConvert.fs

@@ -1188,6 +1188,16 @@ let ``test BigInt ToDecimal works`` () =
     let value = 1.0m
     decimal (bigint value) |> equal value
 
+[<Fact>]
+let ``test BigInt ToDecimal with Decimal.MinValue works`` () =
+    let value = Decimal.MinValue
+    decimal (bigint value) |> equal value
+
+[<Fact>]
+let ``test BigInt ToDecimal with Decimal.MaxValue works`` () =
+    let value = Decimal.MaxValue
+    decimal (bigint value) |> equal value
+
 [<Fact>]
 let ``test BigInt ToString works`` () =
     let value = 1234567890

tests/Rust/tests/src/ConvertTests.fs

@@ -1257,6 +1257,16 @@ let ``BigInt ToDecimal works`` () =
     let value = 1.0m
     decimal (bigint value) |> equal value
 
+[<Fact>]
+let ``BigInt ToDecimal with Decimal.MinValue works`` () =
+    let value = Decimal.MinValue
+    decimal (bigint value) |> equal value
+
+[<Fact>]
+let ``BigInt ToDecimal with Decimal.MaxValue works`` () =
+    let value = Decimal.MaxValue
+    decimal (bigint value) |> equal value
+
 [<Fact>]
 let ``BigInt ToString works`` () =
     let value = 1234567890