Return 0 for tf.sign(NaN) to align with TF

src/kernels/webgl/unaryop_gpu.ts

@@ -15,8 +15,8 @@
  * =============================================================================
  */
 
-import * as selu_util from '../../ops/selu_util';
 import * as erf_util from '../../ops/erf_util';
+import * as selu_util from '../../ops/selu_util';
 
 import {GPGPUProgram} from './gpgpu_math';
 
@@ -70,7 +70,10 @@ export const CEIL = `return ceil(x);`;
 
 export const FLOOR = `return floor(x);`;
 
-export const SIGN = `return sign(x);`;
+export const SIGN = `
+  if (isNaN(x)) { return 0.0; }
+  return sign(x);
+`;
 
 export const ROUND = `
   // OpenGL ES does not support round function.
@@ -175,15 +178,15 @@ export const ATANH = `return (log(1.0 + x) - log(1.0 - x)) / 2.0;`;
 
 export const ERF = `
   // Error function is calculated approximately with elementary function.
-  // See "Handbook of Mathematical Functions with Formulas, 
+  // See "Handbook of Mathematical Functions with Formulas,
   // Graphs, and Mathematical Tables", Abramowitz and Stegun.
   float p = ${erf_util.ERF_P};
   float a1 = ${erf_util.ERF_A1};
   float a2 = ${erf_util.ERF_A2};
   float a3 = ${erf_util.ERF_A3};
   float a4 = ${erf_util.ERF_A4};
   float a5 = ${erf_util.ERF_A5};
-  
+
   float t = 1.0 / (1.0 + p * x);
   return 1.0 - (((((a5*t + a4)*t) + a3)*t + a2)*t + a1)*t*exp(-x*x);
 `;