Created
January 12, 2018 08:54
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Fuck java random
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| public class Psychic { | |
| private static FuckRandom fuckRandom = new FuckRandom(); | |
| static { | |
| fuckRandom.reverse(Math.random()); | |
| } | |
| public static double guess(){ | |
| return fuckRandom.nextDouble(); | |
| } | |
| public static void main(String[] args) { | |
| System.out.println(Psychic.guess()); | |
| System.out.println(Math.random()); | |
| } | |
| } | |
| class FuckRandom extends Random{ | |
| private static final long multiplier = 0x5DEECE66DL; | |
| private static final long addend = 0xBL; | |
| private static final long mask = (1L << 48) - 1; | |
| public void reverse(double prev){ | |
| // return (((long)(next(26)) << 27) + next(27)) * DOUBLE_UNIT; | |
| long numeric = (long) (prev * (1L << 53)); | |
| int old26 = (int) (numeric >>> 27); | |
| int new27 = (int)(numeric & ((1L << 27) - 1)); | |
| long oldSeed26 = ((long) old26 << (48 - 26)) & mask; | |
| long newSeed27 = ((long) new27 << (48 - 27)) & mask; | |
| // BruteForce the old seed | |
| for(long oldSeed = oldSeed26; oldSeed<=(oldSeed26|((1L << (48-26)))); oldSeed++){ | |
| long newSeed = (oldSeed * multiplier + addend) & mask; | |
| if((newSeed & ((1L << 27) - 1) << (48 - 27)) == newSeed27){ | |
| setSeed(newSeed^multiplier); | |
| } | |
| } | |
| } | |
| } |
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More fucker solution is to modify Random class use reflect.