Tiny PRNG (xorshift128), seeded with a string, 175 chars

tinyprng.js

// By Piter Pasma

// (using the xorshift128 PRNG algorithm by Marsaglia)

  seed="Flurp";
  S=Uint32Array.of(9,7,5,3);
  R=(a=1)=>a*(a=S[3],S[3]=S[2],S[2]=S[1],a^=a<<11,S[0]^=a^a>>>8^(S[1]=S[0])>>>19,S[0]/2**32);
  [...seed+'ThxPiter'].map(c=>R(S[3]^=c.charCodeAt()*S[0]));

  // R() is now a function that returns a value between 0 and 1
  // R(a) will return a value between 0 and a

  console.log(1 + Math.floor(R(100))); // outputs integer number between 1 and 100