index.glsl

#define FLOAT_MAX  1.70141184e38
#define FLOAT_MIN  1.17549435e-38

lowp vec4 encode_float(highp float v) {
  highp float av = abs(v);

  //Handle special cases
  if(av < FLOAT_MIN) {
    return vec4(0.0, 0.0, 0.0, 0.0);
  } else if(v > FLOAT_MAX) {
    return vec4(127.0, 128.0, 0.0, 0.0) / 255.0;
  } else if(v < -FLOAT_MAX) {
    return vec4(255.0, 128.0, 0.0, 0.0) / 255.0;
  }

  highp vec4 c = vec4(0,0,0,0);

  //Compute exponent and mantissa
  highp float e = floor(log2(av));
  highp float m = av * pow(2.0, -e) - 1.0;
  
  //Unpack mantissa
  c[1] = floor(128.0 * m);
  m -= c[1] / 128.0;
  c[2] = floor(32768.0 * m);
  m -= c[2] / 32768.0;
  c[3] = floor(8388608.0 * m);
  
  //Unpack exponent
  highp float ebias = e + 127.0;
  c[0] = floor(ebias / 2.0);
  ebias -= c[0] * 2.0;
  c[1] += floor(ebias) * 128.0; 

  //Unpack sign bit
  c[0] += 128.0 * step(0.0, -v);

  //Scale back to range
  return c / 255.0;
}

#pragma glslify: export(encode_float)