handle negative NaNs

Author: MaxGraey

std/assembly/math.ts

@@ -994,7 +994,9 @@ export namespace NativeMath {
 
   @inline
   export function signbit(x: f64): bool {
-    return reinterpret<u64>(x) >>> 63 != 0;
+    // In ECMAScript all NaN values are indistinguishable from each other
+    // so we need handle NaN and negative NaN in similar way
+    return <bool>(<i32>(reinterpret<u64>(x) >>> 63 != 0) & <i32>(x == x));
   }
 
   export function sin(x: f64): f64 { // TODO
@@ -2053,7 +2055,7 @@ export namespace NativeMathf {
 
   @inline
   export function signbit(x: f32): bool {
-    return <bool>(reinterpret<u32>(x) >>> 31);
+    return <bool>((reinterpret<u32>(x) >>> 31) & <i32>(x == x));
   }
 
   export function sin(x: f32): f32 { // TODO

std/portable/index.js

@@ -227,7 +227,7 @@ globalScope["fmodf"] = function fmodf(x, y) {
 
 globalScope["JSMath"] = Math;
 globalScope["JSMath"].signbit = function signbit(x) {
-  F64[0] = x; return Boolean(U64[1] >>> 31);
+  F64[0] = x; return Boolean((U64[1] >>> 31) & (x == x));
 }
 
 globalScope["memory"] = (() => {