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Re: Re: Float16Array

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Re: Re: Float16Array

森建
WebGL 2.0 supports half-precision float (16bit float) by default.
But now, we must use the following dirty hack using `Uint16Array`.

```js
// ref:  
http://stackoverflow.com/questions/32633585/how-do-you-convert-to-half-floats-in-javascript
var toHalf = (function() {

   var floatView = new Float32Array(1);
   var int32View = new Int32Array(floatView.buffer);

   /* This method is faster than the OpenEXR implementation (very often
    * used, eg. in Ogre), with the additional benefit of rounding, inspired
    * by James Tursa?s half-precision code. */
   return function toHalf(val) {

     floatView[0] = val;
     var x = int32View[0];

     var bits = (x >> 16) & 0x8000; /* Get the sign */
     var m = (x >> 12) & 0x07ff; /* Keep one extra bit for rounding */
     var e = (x >> 23) & 0xff; /* Using int is faster here */

     /* If zero, or denormal, or exponent underflows too much for a denormal
      * half, return signed zero. */
     if (e < 103) {
       return bits;
     }

     /* If NaN, return NaN. If Inf or exponent overflow, return Inf. */
     if (e > 142) {
       bits |= 0x7c00;
       /* If exponent was 0xff and one mantissa bit was set, it means NaN,
        * not Inf, so make sure we set one mantissa bit too. */
       bits |= ((e == 255) ? 0 : 1) && (x & 0x007fffff);
       return bits;
     }

     /* If exponent underflows but not too much, return a denormal */
     if (e < 113) {
       m |= 0x0800;
       /* Extra rounding may overflow and set mantissa to 0 and exponent
        * to 1, which is OK. */
       bits |= (m >> (114 - e)) + ((m >> (113 - e)) & 1);
       return bits;
     }

     bits |= ((e - 112) << 10) | (m >> 1);
     /* Extra rounding. An overflow will set mantissa to 0 and increment
      * the exponent, which is OK. */
     bits += m & 1;
     return bits;
   };

}());

var tex = new Uint16Array(4);
tex[0] = toHalf(0.5);
tex[1] = toHalf(1);
tex[2] = toHalf(123);
tex[3] = toHalf(-13);
```

The time has come.

https://en.wikipedia.org/wiki/Half-precision_floating-point_format
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