Optimized version of the Ashima simplex noise 3d

optimizedSnoise3d.glsl

// Optimized AshimaSimplexNoise by @makio64
// Original post on shadertoy : https://www.shadertoy.com/view/Xd3GRf
// Original : https://github.com/ashima/webgl-noise/blob/master/src/noise3D.glsl

vec4 permute(vec4 x){return mod(x*x*34.+x,289.);}
float snoise(vec3 v){
  const vec2 C = 1./vec2(6,3);
  const vec4 D = vec4(0,.5,1,2);
  vec3 i  = floor(v + dot(v, C.yyy));
  vec3 x0 = v - i + dot(i, C.xxx);
  vec3 g = step(x0.yzx, x0.xyz);
  vec3 l = 1. - g;
  vec3 i1 = min( g.xyz, l.zxy );
  vec3 i2 = max( g.xyz, l.zxy );
  vec3 x1 = x0 - i1 + C.x;
  vec3 x2 = x0 - i2 + C.y;
  vec3 x3 = x0 - D.yyy;
  i = mod(i,289.);
  vec4 p = permute( permute( permute(
	  i.z + vec4(0., i1.z, i2.z, 1.))
	+ i.y + vec4(0., i1.y, i2.y, 1.))
	+ i.x + vec4(0., i1.x, i2.x, 1.));
  vec3 ns = .142857142857 * D.wyz - D.xzx;
  vec4 j = p - 49. * floor(p * ns.z * ns.z);
  vec4 x_ = floor(j * ns.z);
  vec4 x = x_ * ns.x + ns.yyyy;
  vec4 y = floor(j - 7. * x_ ) *ns.x + ns.yyyy;
  vec4 h = 1. - abs(x) - abs(y);
  vec4 b0 = vec4( x.xy, y.xy );
  vec4 b1 = vec4( x.zw, y.zw );
  vec4 sh = -step(h, vec4(0));
  vec4 a0 = b0.xzyw + (floor(b0)*2.+ 1.).xzyw*sh.xxyy ;
  vec4 a1 = b1.xzyw + (floor(b1)*2.+ 1.).xzyw*sh.zzww ;
  vec3 p0 = vec3(a0.xy,h.x);
  vec3 p1 = vec3(a0.zw,h.y);
  vec3 p2 = vec3(a1.xy,h.z);
  vec3 p3 = vec3(a1.zw,h.w);
  vec4 norm = inversesqrt(vec4(dot(p0,p0), dot(p1,p1), dot(p2, p2), dot(p3,p3)));
  p0 *= norm.x;
  p1 *= norm.y;
  p2 *= norm.z;
  p3 *= norm.w;
  vec4 m = max(.6 - vec4(dot(x0,x0), dot(x1,x1), dot(x2,x2), dot(x3,x3)), 0.);
  return .5 + 12. * dot( m * m * m, vec4( dot(p0,x0), dot(p1,x1),dot(p2,x2), dot(p3,x3) ) );
}