public static ulong StrToHash(string key)
{
//WARNING! Never use GetHashCode here as it is platform-dependent, but this function must be 100% deterministic
if (key == null)
{
return(0);
}
var sl = key.Length;
if (sl == 0)
{
return(0);
}
ulong hash1 = 0;
for (int i = sl - 1; i > sl - 1 - sizeof(ulong) && i >= 0; i--) //take 8 chars from end (string suffix), for most string the
{ //string tail is the most changing part (i.e. 'Alex Kozloff'/'Alex Richardson'/'System.A'/'System.B'
if (i < sl - 1)
{
hash1 <<= 8;
}
var c = key[i];
var b1 = (c & 0xff00) >> 8;
var b2 = c & 0xff;
hash1 |= (byte)(b1 ^ b2);
}
ulong hash2 = 1566083941ul * (ulong)Adler32.ForString(key);
return(hash1 ^ hash2);
}
/// <summary>
/// Gets sharding ID for string, that is - computes string hash as UInt64 .
/// WARNING! Changing this function will render all existing sharding partitioning invalid. Use extreme care!
/// </summary>
public static ulong StringToShardingID(string key)
{
//WARNING! Never use GetHashCode here as it is platform-dependent, but this function must be 100% deterministic
/*
* From Microsoft on MSDN:
*
* Best Practices for Using Strings in the .NET Framework
*
* Recommendations for String Usage
*
* Use the String.ToUpperInvariant method instead of the String.ToLowerInvariant method when you normalize strings for comparison.
*
* Why? From Microsoft:
*
* Normalize strings to uppercase
*
* There is a small group of characters that when converted to lowercase cannot make a round trip.
*
* What is example of such a character that cannot make a round trip?
*
* Start: Greek Rho Symbol (U+03f1) ϱ
* Uppercase: Capital Greek Rho (U+03a1) Ρ
* Lowercase: Small Greek Rho (U+03c1) ρ
*
* ϱ , Ρ , ρ
*
* That is why, if your want to do case insensitive comparisons you convert the strings to uppercase, and not lowercase.
*/
if (key == null)
{
return(0);
}
#warning DANGER!!!!!!!!! This needs carefull review to not depend on ToUpperInvariant(): todo Dima review!!!
key = key.ToUpperInvariant();
var sl = key.Length;
if (sl == 0)
{
return(0);
}
ulong hash1 = 0;
for (int i = sl - 1; i > sl - 1 - sizeof(ulong) && i >= 0; i--) //take 8 chars from end (string suffix), for most string the
{ //string tail is the most changing part (i.e. 'Alex Kozloff'/'Alex Richardson'/'System.A'/'System.B'
if (i < sl - 1)
{
hash1 <<= 8;
}
var c = key[i];
var b1 = (c & 0xff00) >> 8;
var b2 = c & 0xff;
hash1 |= (byte)(b1 ^ b2);
}
ulong hash2 = 1566083941ul * (ulong)Adler32.ForString(key);
return(hash1 ^ hash2);
}
public void Adler32_5()
{
Assert.AreEqual(UInt32.Parse("11E60398", System.Globalization.NumberStyles.HexNumber),
Adler32.ForString("Wikipedia"));
}
public void Adler32_4()
{
Assert.AreEqual(UInt32.Parse("36E81466", System.Globalization.NumberStyles.HexNumber),
Adler32.ForString("This is an example of a much longer string of characters"));
}
public void Adler32_3()
{
Assert.AreEqual(UInt32.Parse("1BE9043A", System.Globalization.NumberStyles.HexNumber),
Adler32.ForString("Hello Dolly!"));
}