Messages in this thread | | | Date | Fri, 3 Apr 2020 22:40:37 +0200 | From | Pali Rohár <> | Subject | Re: [PATCH 1/4] exfat: Simplify exfat_utf8_d_hash() for code points above U+FFFF |
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On Friday 03 April 2020 02:18:15 Kohada.Tetsuhiro@dc.MitsubishiElectric.co.jp wrote: > > I guess it was designed for 8bit types, not for long (64bit types) and > > I'm not sure how effective it is even for 16bit types for which it is > > already used. > > In partial_name_hash (), when 8bit value or 16bit value is specified, > upper 8-12bits tend to be 0. > > > So question is, what should we do for either 21bit number (one Unicode > > code point = equivalent of UTF-32) or for sequence of 16bit numbers > > (UTF-16)? > > If you want to get an unbiased hash value by specifying an 8 or 16-bit value,
Hello! In exfat we have sequence of 21-bit values (not 8, not 16).
> the hash32() function is a good choice. > ex1: Prepare by hash32 () function. > hash = partial_name_hash (hash32 (val16,32), hash); > ex2: Use the hash32() function directly. > hash + = hash32 (val16,32);
Did you mean hash_32() function from linux/hash.h?
> > partial_name_hash(unsigned long c, unsigned long prevhash) > > { > > return (prevhash + (c << 4) + (c >> 4)) * 11; > > } > > Another way may replace partial_name_hash(). > > return prevhash + hash32(c,32) >
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