float random(vec2 st) {
    return fract(sin(dot(st.xy,
                         vec2(12.9898,78.233)))*
        43758.5453123);
}

float noise(float x) {
  float i = floor(x);
  float f = fract(x);
  return mix(rand(i), rand(i + 1.0), smoothstep(0.,1.,f));
}