Fix float64 to uint{8,16,32} conversion.

nevkontakte · nevkontakte · commit 4f6746f066f3 · 2024-05-06T19:18:21.000+01:00
Before this change, GopherJS compiler emitted `(f >> 0)` expression to convert a float64 `f` to any non-64-bit unsigned integer type. This is incorrect, because `>>` is a signed bitshift operator in JS, so the returned value remained signed. Moreover, it did not take into account to bit size of the target type. By removing the switch cause, we make the compiler fall through to the default clause where `fc.fixNumber()` actually does the right thing, taking the target into account. Fixes #733.
diff --git a/compiler/expressions.go b/compiler/expressions.go
@@ -1128,8 +1128,6 @@ func (fc *funcContext) translateConversion(expr ast.Expr, desiredType types.Type
 					return fc.fixNumber(fc.formatParenExpr("%1l + ((%1h >> 31) * 4294967296)", expr), t)
 				}
 				return fc.fixNumber(fc.formatExpr("%s.$low", fc.translateExpr(expr)), t)
-			case isFloat(basicExprType):
-				return fc.formatParenExpr("%e >> 0", expr)
 			case types.Identical(exprType, types.Typ[types.UnsafePointer]):
 				return fc.translateExpr(expr)
 			default:
diff --git a/tests/numeric_test.go b/tests/numeric_test.go
@@ -5,6 +5,8 @@ import (
 	"runtime"
 	"testing"
 	"testing/quick"
+
+	"github.com/gopherjs/gopherjs/js"
 )
 
 // naiveMul64 performs 64-bit multiplication without using the multiplication
@@ -93,3 +95,26 @@ func BenchmarkMul64(b *testing.B) {
 		}
 	})
 }
+
+func TestIssue733(t *testing.T) {
+	if runtime.GOOS != "js" {
+		t.Skip("test uses GopherJS-specific features")
+	}
+
+	t.Run("sign", func(t *testing.T) {
+		f := float64(-1)
+		i := uint32(f)
+		underlying := js.InternalObject(i).Float() // Get the raw JS number behind i.
+		if want := float64(4294967295); underlying != want {
+			t.Errorf("Got: uint32(float64(%v)) = %v. Want: %v.", f, underlying, want)
+		}
+	})
+	t.Run("truncation", func(t *testing.T) {
+		f := float64(300)
+		i := uint8(f)
+		underlying := js.InternalObject(i).Float() // Get the raw JS number behind i.
+		if want := float64(44); underlying != want {
+			t.Errorf("Got: uint32(float64(%v)) = %v. Want: %v.", f, underlying, want)
+		}
+	})
+}

Original file line number	Diff line number	Diff line change
`@@ -1128,8 +1128,6 @@ func (fc *funcContext) translateConversion(expr ast.Expr, desiredType types.Type`
`1128`	`1128`	`return fc.fixNumber(fc.formatParenExpr("%1l + ((%1h >> 31) * 4294967296)", expr), t)`
`1129`	`1129`	`}`
`1130`	`1130`	`return fc.fixNumber(fc.formatExpr("%s.$low", fc.translateExpr(expr)), t)`
`1131`		`- case isFloat(basicExprType):`
`1132`		`- return fc.formatParenExpr("%e >> 0", expr)`
`1133`	`1131`	`case types.Identical(exprType, types.Typ[types.UnsafePointer]):`
`1134`	`1132`	`return fc.translateExpr(expr)`
`1135`	`1133`	`default:`