Add Math.signbit (#333)

std/assembly/index.d.ts

@@ -762,6 +762,8 @@ interface IMath<T> {
   round(x: T): T;
   /** Returns the sign of `x`, indicating whether the number is positive, negative or zero. */
   sign(x: T): T;
+  /** Returns whether the sign bit of `x` is set */
+  signbit(x: T): bool;
   /** Returns the sine of `x`. */
   sin(x: T): T;
   /** Returns the hyperbolic sine of `x`. */

std/assembly/math.ts

@@ -992,6 +992,13 @@ export namespace NativeMath {
     }
   }
 
+  @inline
+  export function signbit(x: f64): bool {
+    // 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) & (x == x));
+  }
+
   export function sin(x: f64): f64 { // TODO
     unreachable();
     return 0;
@@ -2046,6 +2053,11 @@ export namespace NativeMathf {
     }
   }
 
+  @inline
+  export function signbit(x: f32): bool {
+    return <bool>((reinterpret<u32>(x) >>> 31) & (x == x));
+  }
+
   export function sin(x: f32): f32 { // TODO
     unreachable();
     return 0;

std/portable/index.d.ts

@@ -556,6 +556,7 @@ interface IMath {
   random(): f64;
   round(x: f64): f64;
   sign(x: f64): f64;
+  signbit(x: f64): bool;
   sin(x: f64): f64;
   sinh(x: f64): f64;
   sqrt(x: f64): f64;

std/portable/index.js

@@ -4,6 +4,9 @@ var globalScope = typeof window !== "undefined" && window || typeof global !== "
 
 globalScope.ASC_TARGET = 0;
 
+var F64 = new Float64Array(1);
+var U64 = new Uint32Array(F64.buffer);
+
 Object.defineProperties(
   globalScope["i8"] = function i8(value) { return value << 24 >> 24; }
 , {
@@ -210,7 +213,7 @@ globalScope["isString"] = function isString(arg) {
 
 globalScope["isArray"] = Array.isArray;
 
-globalScope["unchecked"] = function(expr) {
+globalScope["unchecked"] = function unchecked(expr) {
   return expr;
 };
 
@@ -223,6 +226,9 @@ globalScope["fmodf"] = function fmodf(x, y) {
 };
 
 globalScope["JSMath"] = Math;
+globalScope["JSMath"].signbit = function signbit(x) {
+  F64[0] = x; return Boolean((U64[1] >>> 31) & (x == x));
+}
 
 globalScope["memory"] = (() => {
   var HEAP = new Uint8Array(0);