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Zero/ZeroLevel.HNSW/Utils/FastRandom.cs

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Update HNSW
3 years ago
using System;
using System.Runtime.CompilerServices;
namespace ZeroLevel.HNSW
{
public sealed class DefaultRandomGenerator
{
/// <summary>
/// This is the default configuration (it supports the optimization process to be executed on multiple threads)
/// </summary>
public static DefaultRandomGenerator Instance { get; } = new DefaultRandomGenerator(allowParallel: true);
/// <summary>
/// This uses the same random number generator but forces the optimization process to run on a single thread (which may be desirable if multiple requests may be processed concurrently
/// or if it is otherwise not desirable to let a single request access all of the CPUs)
/// </summary>
public static DefaultRandomGenerator DisableThreading { get; } = new DefaultRandomGenerator(allowParallel: false);
private DefaultRandomGenerator(bool allowParallel) => IsThreadSafe = allowParallel;
public bool IsThreadSafe { get; }
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public int Next(int minValue, int maxValue) => ThreadSafeFastRandom.Next(minValue, maxValue);
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public float NextFloat() => ThreadSafeFastRandom.NextFloat();
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public void NextFloats(Span<float> buffer) => ThreadSafeFastRandom.NextFloats(buffer);
}
internal static class ThreadSafeFastRandom
{
private static readonly Random _global = new Random();
[ThreadStatic]
private static FastRandom _local;
private static int GetGlobalSeed()
{
int seed;
lock (_global)
{
seed = _global.Next();
}
return seed;
}
/// <summary>
/// Returns a non-negative random integer.
/// </summary>
/// <returns>A 32-bit signed integer that is greater than or equal to 0 and less than System.Int32.MaxValue.</returns>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static int Next()
{
var inst = _local;
if (inst == null)
{
int seed;
seed = GetGlobalSeed();
_local = inst = new FastRandom(seed);
}
return inst.Next();
}
/// <summary>
/// Returns a non-negative random integer that is less than the specified maximum.
/// </summary>
/// <param name="maxValue">The exclusive upper bound of the random number to be generated. maxValue must be greater than or equal to 0.</param>
/// <returns>A 32-bit signed integer that is greater than or equal to 0, and less than maxValue; that is, the range of return values ordinarily includes 0 but not maxValue. However,
// if maxValue equals 0, maxValue is returned.</returns>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static int Next(int maxValue)
{
var inst = _local;
if (inst == null)
{
int seed;
seed = GetGlobalSeed();
_local = inst = new FastRandom(seed);
}
int ans;
do
{
ans = inst.Next(maxValue);
} while (ans == maxValue);
return ans;
}
/// <summary>
/// Returns a random integer that is within a specified range.
/// </summary>
/// <param name="minValue">The inclusive lower bound of the random number returned.</param>
/// <param name="maxValue">The exclusive upper bound of the random number returned. maxValue must be greater than or equal to minValue.</param>
/// <returns>A 32-bit signed integer greater than or equal to minValue and less than maxValue; that is, the range of return values includes minValue but not maxValue. If minValue
// equals maxValue, minValue is returned.</returns>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static int Next(int minValue, int maxValue)
{
var inst = _local;
if (inst == null)
{
int seed;
seed = GetGlobalSeed();
_local = inst = new FastRandom(seed);
}
return inst.Next(minValue, maxValue);
}
/// <summary>
/// Generates a random float. Values returned are from 0.0 up to but not including 1.0.
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static float NextFloat()
{
var inst = _local;
if (inst == null)
{
int seed;
seed = GetGlobalSeed();
_local = inst = new FastRandom(seed);
}
return inst.NextFloat();
}
/// <summary>
/// Fills the elements of a specified array of bytes with random numbers.
/// </summary>
/// <param name="buffer">An array of bytes to contain random numbers.</param>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static void NextFloats(Span<float> buffer)
{
var inst = _local;
if (inst == null)
{
int seed;
seed = GetGlobalSeed();
_local = inst = new FastRandom(seed);
}
inst.NextFloats(buffer);
}
}
/// <summary>
/// A fast random number generator for .NET, from https://www.codeproject.com/Articles/9187/A-fast-equivalent-for-System-Random
/// Colin Green, January 2005
///
/// September 4th 2005
/// Added NextBytesUnsafe() - commented out by default.
/// Fixed bug in Reinitialise() - y,z and w variables were not being reset.
///
/// Key points:
/// 1) Based on a simple and fast xor-shift pseudo random number generator (RNG) specified in:
/// Marsaglia, George. (2003). Xorshift RNGs.
/// http://www.jstatsoft.org/v08/i14/xorshift.pdf
///
/// This particular implementation of xorshift has a period of 2^128-1. See the above paper to see
/// how this can be easily extened if you need a longer period. At the time of writing I could find no
/// information on the period of System.Random for comparison.
///
/// 2) Faster than System.Random. Up to 8x faster, depending on which methods are called.
///
/// 3) Direct replacement for System.Random. This class implements all of the methods that System.Random
/// does plus some additional methods. The like named methods are functionally equivalent.
///
/// 4) Allows fast re-initialisation with a seed, unlike System.Random which accepts a seed at construction
/// time which then executes a relatively expensive initialisation routine. This provides a vast speed improvement
/// if you need to reset the pseudo-random number sequence many times, e.g. if you want to re-generate the same
/// sequence many times. An alternative might be to cache random numbers in an array, but that approach is limited
/// by memory capacity and the fact that you may also want a large number of different sequences cached. Each sequence
/// can each be represented by a single seed value (int) when using FastRandom.
///
/// Notes.
/// A further performance improvement can be obtained by declaring local variables as static, thus avoiding
/// re-allocation of variables on each call. However care should be taken if multiple instances of
/// FastRandom are in use or if being used in a multi-threaded environment.
///
/// </summary>
internal class FastRandom
{
// The +1 ensures NextDouble doesn't generate 1.0
const float FLOAT_UNIT_INT = 1.0f / ((float)int.MaxValue + 1.0f);
const double REAL_UNIT_INT = 1.0 / ((double)int.MaxValue + 1.0);
const double REAL_UNIT_UINT = 1.0 / ((double)uint.MaxValue + 1.0);
const uint Y = 842502087, Z = 3579807591, W = 273326509;
uint x, y, z, w;
/// <summary>
/// Initialises a new instance using time dependent seed.
/// </summary>
public FastRandom()
{
// Initialise using the system tick count.
Reinitialise(Environment.TickCount);
}
/// <summary>
/// Initialises a new instance using an int value as seed.
/// This constructor signature is provided to maintain compatibility with
/// System.Random
/// </summary>
public FastRandom(int seed)
{
Reinitialise(seed);
}
/// <summary>
/// Reinitialises using an int value as a seed.
/// </summary>
public void Reinitialise(int seed)
{
// The only stipulation stated for the xorshift RNG is that at least one of
// the seeds x,y,z,w is non-zero. We fulfill that requirement by only allowing
// resetting of the x seed
x = (uint)seed;
y = Y;
z = Z;
w = W;
}
/// <summary>
/// Generates a random int over the range 0 to int.MaxValue-1.
/// MaxValue is not generated in order to remain functionally equivalent to System.Random.Next().
/// This does slightly eat into some of the performance gain over System.Random, but not much.
/// For better performance see:
///
/// Call NextInt() for an int over the range 0 to int.MaxValue.
///
/// Call NextUInt() and cast the result to an int to generate an int over the full Int32 value range
/// including negative values.
/// </summary>
public int Next()
{
uint t = (x ^ (x << 11));
x = y; y = z; z = w;
w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));
// Handle the special case where the value int.MaxValue is generated. This is outside of
// the range of permitted values, so we therefore call Next() to try again.
uint rtn = w & 0x7FFFFFFF;
if (rtn == 0x7FFFFFFF)
return Next();
return (int)rtn;
}
/// <summary>
/// Generates a random int over the range 0 to upperBound-1, and not including upperBound.
/// </summary>
public int Next(int upperBound)
{
if (upperBound < 0)
throw new ArgumentOutOfRangeException("upperBound", upperBound, "upperBound must be >=0");
uint t = (x ^ (x << 11));
x = y; y = z; z = w;
// The explicit int cast before the first multiplication gives better performance.
// See comments in NextDouble.
return (int)((REAL_UNIT_INT * (int)(0x7FFFFFFF & (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8))))) * upperBound);
}
/// <summary>
/// Generates a random int over the range lowerBound to upperBound-1, and not including upperBound.
/// upperBound must be >= lowerBound. lowerBound may be negative.
/// </summary>
public int Next(int lowerBound, int upperBound)
{
if (lowerBound > upperBound)
throw new ArgumentOutOfRangeException("upperBound", upperBound, "upperBound must be >=lowerBound");
uint t = (x ^ (x << 11));
x = y; y = z; z = w;
// The explicit int cast before the first multiplication gives better performance.
// See comments in NextDouble.
int range = upperBound - lowerBound;
if (range < 0)
{ // If range is <0 then an overflow has occured and must resort to using long integer arithmetic instead (slower).
// We also must use all 32 bits of precision, instead of the normal 31, which again is slower.
return lowerBound + (int)((REAL_UNIT_UINT * (double)(w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)))) * (double)((long)upperBound - (long)lowerBound));
}
// 31 bits of precision will suffice if range<=int.MaxValue. This allows us to cast to an int and gain
// a little more performance.
return lowerBound + (int)((REAL_UNIT_INT * (double)(int)(0x7FFFFFFF & (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8))))) * (double)range);
}
/// <summary>
/// Generates a random double. Values returned are from 0.0 up to but not including 1.0.
/// </summary>
public double NextDouble()
{
uint t = (x ^ (x << 11));
x = y; y = z; z = w;
// Here we can gain a 2x speed improvement by generating a value that can be cast to
// an int instead of the more easily available uint. If we then explicitly cast to an
// int the compiler will then cast the int to a double to perform the multiplication,
// this final cast is a lot faster than casting from a uint to a double. The extra cast
// to an int is very fast (the allocated bits remain the same) and so the overall effect
// of the extra cast is a significant performance improvement.
//
// Also note that the loss of one bit of precision is equivalent to what occurs within
// System.Random.
return (REAL_UNIT_INT * (int)(0x7FFFFFFF & (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)))));
}
/// <summary>
/// Generates a random double. Values returned are from 0.0 up to but not including 1.0.
/// </summary>
public float NextFloat()
{
uint x = this.x, y = this.y, z = this.z, w = this.w;
uint t = (x ^ (x << 11));
x = y; y = z; z = w;
w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));
var value = FLOAT_UNIT_INT * (int)(0x7FFFFFFF & w);
this.x = x; this.y = y; this.z = z; this.w = w;
return value;
}
/// <summary>
/// Fills the provided byte array with random floats.
/// </summary>
public void NextFloats(Span<float> buffer)
{
uint x = this.x, y = this.y, z = this.z, w = this.w;
int i = 0;
uint t;
for (int bound = buffer.Length; i < bound;)
{
t = (x ^ (x << 11));
x = y; y = z; z = w;
w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));
buffer[i++] = FLOAT_UNIT_INT * (int)(0x7FFFFFFF & w);
}
this.x = x; this.y = y; this.z = z; this.w = w;
}
/// <summary>
/// Fills the provided byte array with random bytes.
/// This method is functionally equivalent to System.Random.NextBytes().
/// </summary>
public void NextBytes(byte[] buffer)
{
// Fill up the bulk of the buffer in chunks of 4 bytes at a time.
uint x = this.x, y = this.y, z = this.z, w = this.w;
int i = 0;
uint t;
for (int bound = buffer.Length - 3; i < bound;)
{
// Generate 4 bytes.
// Increased performance is achieved by generating 4 random bytes per loop.
// Also note that no mask needs to be applied to zero out the higher order bytes before
// casting because the cast ignores thos bytes. Thanks to Stefan Troschütz for pointing this out.
t = (x ^ (x << 11));
x = y; y = z; z = w;
w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));
buffer[i++] = (byte)w;
buffer[i++] = (byte)(w >> 8);
buffer[i++] = (byte)(w >> 16);
buffer[i++] = (byte)(w >> 24);
}
// Fill up any remaining bytes in the buffer.
if (i < buffer.Length)
{
// Generate 4 bytes.
t = (x ^ (x << 11));
x = y; y = z; z = w;
w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));
buffer[i++] = (byte)w;
if (i < buffer.Length)
{
buffer[i++] = (byte)(w >> 8);
if (i < buffer.Length)
{
buffer[i++] = (byte)(w >> 16);
if (i < buffer.Length)
{
buffer[i] = (byte)(w >> 24);
}
}
}
}
this.x = x; this.y = y; this.z = z; this.w = w;
}
/// <summary>
/// Fills the provided byte array with random bytes.
/// This method is functionally equivalent to System.Random.NextBytes().
/// </summary>
public void NextBytes(Span<byte> buffer)
{
// Fill up the bulk of the buffer in chunks of 4 bytes at a time.
uint x = this.x, y = this.y, z = this.z, w = this.w;
int i = 0;
uint t;
for (int bound = buffer.Length - 3; i < bound;)
{
// Generate 4 bytes.
// Increased performance is achieved by generating 4 random bytes per loop.
// Also note that no mask needs to be applied to zero out the higher order bytes before
// casting because the cast ignores thos bytes. Thanks to Stefan Troschütz for pointing this out.
t = (x ^ (x << 11));
x = y; y = z; z = w;
w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));
buffer[i++] = (byte)w;
buffer[i++] = (byte)(w >> 8);
buffer[i++] = (byte)(w >> 16);
buffer[i++] = (byte)(w >> 24);
}
// Fill up any remaining bytes in the buffer.
if (i < buffer.Length)
{
// Generate 4 bytes.
t = (x ^ (x << 11));
x = y; y = z; z = w;
w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));
buffer[i++] = (byte)w;
if (i < buffer.Length)
{
buffer[i++] = (byte)(w >> 8);
if (i < buffer.Length)
{
buffer[i++] = (byte)(w >> 16);
if (i < buffer.Length)
{
buffer[i] = (byte)(w >> 24);
}
}
}
}
this.x = x; this.y = y; this.z = z; this.w = w;
}
/// <summary>
/// Generates a uint. Values returned are over the full range of a uint,
/// uint.MinValue to uint.MaxValue, inclusive.
///
/// This is the fastest method for generating a single random number because the underlying
/// random number generator algorithm generates 32 random bits that can be cast directly to
/// a uint.
/// </summary>
public uint NextUInt()
{
uint t = (x ^ (x << 11));
x = y; y = z; z = w;
return (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)));
}
/// <summary>
/// Generates a random int over the range 0 to int.MaxValue, inclusive.
/// This method differs from Next() only in that the range is 0 to int.MaxValue
/// and not 0 to int.MaxValue-1.
///
/// The slight difference in range means this method is slightly faster than Next()
/// but is not functionally equivalent to System.Random.Next().
/// </summary>
public int NextInt()
{
uint t = (x ^ (x << 11));
x = y; y = z; z = w;
return (int)(0x7FFFFFFF & (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8))));
}
// Buffer 32 bits in bitBuffer, return 1 at a time, keep track of how many have been returned
// with bitBufferIdx.
uint bitBuffer;
uint bitMask = 1;
/// <summary>
/// Generates a single random bit.
/// This method's performance is improved by generating 32 bits in one operation and storing them
/// ready for future calls.
/// </summary>
public bool NextBool()
{
if (bitMask == 1)
{
// Generate 32 more bits.
uint t = (x ^ (x << 11));
x = y; y = z; z = w;
bitBuffer = w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));
// Reset the bitMask that tells us which bit to read next.
bitMask = 0x80000000;
return (bitBuffer & bitMask) == 0;
}
return (bitBuffer & (bitMask >>= 1)) == 0;
}
}
}

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