periodic noise by Iñigo Quilez from ShaderToy

gistfile1.txt

float hash( float n )
{
    return fract(sin(n)*43758.5453);
}

float noise( vec3 x )
{
    // The noise function returns a value in the range -1.0f -> 1.0f

    vec3 p = floor(x);
    vec3 f = fract(x);

    f       = f*f*(3.0-2.0*f);
    float n = p.x + p.y*57.0 + 113.0*p.z;

    return mix(     mix( mix( hash(n), hash(n+1.), f.x ), mix( hash(n+57.), hash(n+58.),f.x ), f.y ),
                    mix( mix( hash(n+113.0), hash(n+114.),f.x), mix( hash(n+170.), hash(n+171.),f.x ), f.y ),
                    f.z);
}