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

nevkontakte · nevkontakte · commit 7321e751af50 · 2024-05-06T18:56:26.000+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/lowlevel_test.go b/tests/lowlevel_test.go
@@ -9,6 +9,7 @@ import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
+	"github.com/gopherjs/gopherjs/js"
 )
 
 // Test for internalization/externalization of time.Time/Date when time package is imported
@@ -49,3 +50,22 @@ func TestDeferBuiltin(t *testing.T) {
 		t.Fatalf("%v:\n%s", err, got)
 	}
 }
+
+func TestIssue733(t *testing.T) {
+	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:`