Package io.sentry.util

Class Random

java.lang.Object

io.sentry.util.Random

All Implemented Interfaces:

Serializable

@Internal
public final class Random
extends Object
implements Serializable

A simplified version of Random that we use for sampling, which is much faster than SecureRandom. This is necessary so that some security tools do not flag our Random usage as potentially insecure.

See Also:

• Serialized Form

Constructor Summary

Constructors

Constructor	Description
Random()	Creates a new random number generator.
Random(long seed)	Creates a new random number generator using a single long seed.

Method Summary

Modifier and Type	Method	Description
boolean	nextBoolean()	Returns the next pseudorandom, uniformly distributed boolean value from this random number generator's sequence.
void	nextBytes(byte[] bytes)	Generates random bytes and places them into a user-supplied byte array.
double	nextDouble()	Returns the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence.
float	nextFloat()	Returns the next pseudorandom, uniformly distributed float value between 0.0 and 1.0 from this random number generator's sequence.
int	nextInt()	Returns the next pseudorandom, uniformly distributed int value from this random number generator's sequence.
int	nextInt(int bound)	Returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence.
long	nextLong()	Returns the next pseudorandom, uniformly distributed long value from this random number generator's sequence.
void	setSeed(long seed)	Sets the seed of this random number generator using a single long seed.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

Random

public Random()

Creates a new random number generator. This constructor sets the seed of the random number generator to a value very likely to be distinct from any other invocation of this constructor.

Random

public Random(long seed)

Creates a new random number generator using a single long seed. The seed is the initial value of the internal state of the pseudorandom number generator which is maintained by method next(int).

The invocation new Random(seed) is equivalent to:

 Random rnd = new Random();
 rnd.setSeed(seed);
 

Parameters:

seed - the initial seed

See Also:

• setSeed(long)

Method Details

setSeed

public void setSeed(long seed)

Sets the seed of this random number generator using a single long seed. The general contract of setSeed is that it alters the state of this random number generator object so as to be in exactly the same state as if it had just been created with the argument seed as a seed. The method setSeed is implemented by class Random by atomically updating the seed to

(seed ^ 0x5DEECE66DL) & ((1L << 48) - 1)

The implementation of setSeed by class Random happens to use only 48 bits of the given seed. In general, however, an overriding method may use all 64 bits of the long argument as a seed value.

Parameters:

seed - the initial seed

nextBytes

public void nextBytes(byte[] bytes)

Generates random bytes and places them into a user-supplied byte array. The number of random bytes produced is equal to the length of the byte array.

The method nextBytes is implemented by class Random as if by:

 public void nextBytes(byte[] bytes) {
   for (int i = 0; i < bytes.length; )
     for (int rnd = nextInt(), n = Math.min(bytes.length - i, 4);
          n-- > 0; rnd >>= 8)
       bytes[i++] = (byte)rnd;
 }
 

Parameters:

bytes - the byte array to fill with random bytes

Throws:

NullPointerException - if the byte array is null

Since:

1.1

nextInt

public int nextInt()

Returns the next pseudorandom, uniformly distributed int value from this random number generator's sequence. The general contract of nextInt is that one int value is pseudorandomly generated and returned. All 2³² possible int values are produced with (approximately) equal probability.

The method nextInt is implemented by class Random as if by:

 public int nextInt() {
   return next(32);
 }
 

Returns:

the next pseudorandom, uniformly distributed int value from this random number generator's sequence

nextInt

public int nextInt(int bound)

Returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence. The general contract of nextInt is that one int value in the specified range is pseudorandomly generated and returned. All bound possible int values are produced with (approximately) equal probability. The method nextInt(int bound) is implemented by class Random as if by:

 public int nextInt(int bound) {
   if (bound <= 0)
     throw new IllegalArgumentException("bound must be positive");

   if ((bound & -bound) == bound)  // i.e., bound is a power of 2
     return (int)((bound * (long)next(31)) >> 31);

   int bits, val;
   do {
       bits = next(31);
       val = bits % bound;
   } while (bits - val + (bound-1) < 0);
   return val;
 }
 

The hedge "approximately" is used in the foregoing description only because the next method is only approximately an unbiased source of independently chosen bits. If it were a perfect source of randomly chosen bits, then the algorithm shown would choose int values from the stated range with perfect uniformity.

The algorithm is slightly tricky. It rejects values that would result in an uneven distribution (due to the fact that 2^31 is not divisible by n). The probability of a value being rejected depends on n. The worst case is n=2^30+1, for which the probability of a reject is 1/2, and the expected number of iterations before the loop terminates is 2.

The algorithm treats the case where n is a power of two specially: it returns the correct number of high-order bits from the underlying pseudo-random number generator. In the absence of special treatment, the correct number of low-order bits would be returned. Linear congruential pseudo-random number generators such as the one implemented by this class are known to have short periods in the sequence of values of their low-order bits. Thus, this special case greatly increases the length of the sequence of values returned by successive calls to this method if n is a small power of two.

Parameters:

bound - the upper bound (exclusive). Must be positive.

Returns:

the next pseudorandom, uniformly distributed int value between zero (inclusive) and bound (exclusive) from this random number generator's sequence

Throws:

IllegalArgumentException - if bound is not positive

Since:

1.2

nextLong

public long nextLong()

Returns the next pseudorandom, uniformly distributed long value from this random number generator's sequence. The general contract of nextLong is that one long value is pseudorandomly generated and returned.

The method nextLong is implemented by class Random as if by:

 public long nextLong() {
   return ((long)next(32) << 32) + next(32);
 }
 

Because class Random uses a seed with only 48 bits, this algorithm will not return all possible long values.

Returns:

the next pseudorandom, uniformly distributed long value from this random number generator's sequence

nextBoolean

public boolean nextBoolean()

Returns the next pseudorandom, uniformly distributed boolean value from this random number generator's sequence. The general contract of nextBoolean is that one boolean value is pseudorandomly generated and returned. The values true and false are produced with (approximately) equal probability.

The method nextBoolean is implemented by class Random as if by:

 public boolean nextBoolean() {
   return next(1) != 0;
 }
 

Returns:

the next pseudorandom, uniformly distributed boolean value from this random number generator's sequence

Since:

1.2

nextFloat

public float nextFloat()

Returns the next pseudorandom, uniformly distributed float value between 0.0 and 1.0 from this random number generator's sequence.

The general contract of nextFloat is that one float value, chosen (approximately) uniformly from the range 0.0f (inclusive) to 1.0f (exclusive), is pseudorandomly generated and returned. All 2²⁴ possible float values of the form m x 2^-24, where m is a positive integer less than 2²⁴, are produced with (approximately) equal probability.

The method nextFloat is implemented by class Random as if by:

 public float nextFloat() {
   return next(24) / ((float)(1 << 24));
 }
 

The hedge "approximately" is used in the foregoing description only because the next method is only approximately an unbiased source of independently chosen bits. If it were a perfect source of randomly chosen bits, then the algorithm shown would choose float values from the stated range with perfect uniformity.

[In early versions of Java, the result was incorrectly calculated as:

 return next(30) / ((float)(1 << 30));
 

This might seem to be equivalent, if not better, but in fact it introduced a slight nonuniformity because of the bias in the rounding of floating-point numbers: it was slightly more likely that the low-order bit of the significand would be 0 than that it would be 1.]

Returns:

the next pseudorandom, uniformly distributed float value between 0.0 and 1.0 from this random number generator's sequence

nextDouble

public double nextDouble()

Returns the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence.

The general contract of nextDouble is that one double value, chosen (approximately) uniformly from the range 0.0d (inclusive) to 1.0d (exclusive), is pseudorandomly generated and returned.

The method nextDouble is implemented by class Random as if by:

 public double nextDouble() {
   return (((long)next(26) << 27) + next(27))
     / (double)(1L << 53);
 }
 

The hedge "approximately" is used in the foregoing description only because the next method is only approximately an unbiased source of independently chosen bits. If it were a perfect source of randomly chosen bits, then the algorithm shown would choose double values from the stated range with perfect uniformity.

[In early versions of Java, the result was incorrectly calculated as:

 return (((long)next(27) << 27) + next(27))
   / (double)(1L << 54);
 

This might seem to be equivalent, if not better, but in fact it introduced a large nonuniformity because of the bias in the rounding of floating-point numbers: it was three times as likely that the low-order bit of the significand would be 0 than that it would be 1! This nonuniformity probably doesn't matter much in practice, but we strive for perfection.]

Returns:

the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence

See Also:

• Math.random()