Rate  u32  u64
u32 54.9/s   -- -13%
u64 63.3/s  15%   --

##</code><code>##

#!/usr/bin/perl

use strict;
use warnings;
use Digest::JHash;
use Benchmark qw(cmpthese);

my @dat;
for my $i (1..100) {
    $dat[$i] = '';
    $dat[$i] .= chr(int(rand(256))) for 1..100000;
}

cmpthese (100,
{
    u32 => sub {
               for (1..100) {
                   my $h = Digest::JHash::jhash($dat[$_]);
               }
           },

    u64 => sub {
               for (1..100) {
                   my $h = Digest::JHash::jhash_orig($dat[$_]);
               }
           },
} );

##</code><code>##

#define MASK32 0xffffffff

#define MIX(a,b,c) \
{ \
  a -= b; a &= MASK32; a -= c; a &= MASK32; a ^= ((c>>13)); \
  b -= c; b &= MASK32; b -= a; b &= MASK32; b ^= ((a<<8)  & MASK32); \
  c -= a; c &= MASK32; c -= b; c &= MASK32; c ^= ((b>>13)); \
  a -= b; a &= MASK32; a -= c; a &= MASK32; a ^= ((c>>12)); \
  b -= c; b &= MASK32; b -= a; b &= MASK32; b ^= ((a<<16) & MASK32); \
  c -= a; c &= MASK32; c -= b; c &= MASK32; c ^= ((b>>5) ); \
  a -= b; a &= MASK32; a -= c; a &= MASK32; a ^= ((c>>3) ); \
  b -= c; b &= MASK32; b -= a; b &= MASK32; b ^= ((a<<10) & MASK32); \
  c -= a; c &= MASK32; c -= b; c &= MASK32; c ^= ((b>>15)); \
}

unsigned long jhash( SV* str )
{
    STRLEN rawlen;
    char* p;
    unsigned long a, b, c, len, length;

    /* extract the string data and string length from the perl scalar */
    p = (char*)SvPV(str, rawlen);
    length = len = (unsigned long)rawlen;

    /* Test for undef or null string case and return 0 */
    if ( length == 0 ) {
        DEBUG && printf( "Recieved a null or undef string!\n" );
      return 0;
    }

    DEBUG && printf( "Received string '%.*s'.\n", (int)len, p );

    a = b = 0x9e3779b9;        /* golden ratio suggested by Jenkins */
    c = 0;
    while (len >= 12)
    {
        a += (p[0] + ((((unsigned long)p[1]) <<  8) & MASK32 )
                   + ((((unsigned long)p[2]) << 16) & MASK32 )
                   + ((((unsigned long)p[3]) << 24) & MASK32 )); a &= MASK32;
        b += (p[4] + ((((unsigned long)p[5]) <<  8) & MASK32 )
                   + ((((unsigned long)p[6]) << 16) & MASK32 )
                   + ((((unsigned long)p[7]) << 24) & MASK32 )); b &= MASK32;
        c += (p[8] + ((((unsigned long)p[9]) <<  8) & MASK32 )
                   + ((((unsigned long)p[10])<< 16) & MASK32 )
                   + ((((unsigned long)p[11])<< 24) & MASK32 )); c &= MASK32;
        MIX(a, b, c);
        p += 12;
        len -= 12;
    }
    c += length;
    switch(len) {
    case 11: c+=(((unsigned int)p[10]<< 24) & MASK32 ); c &= MASK32;
    case 10: c+=(((unsigned int)p[9] << 16) & MASK32 ); c &= MASK32;
    case 9:  c+=(((unsigned int)p[8] <<  8) & MASK32 ); c &= MASK32;
    case 8:  b+=(((unsigned int)p[7] << 24) & MASK32 ); b &= MASK32;
    case 7:  b+=(((unsigned int)p[6] << 16) & MASK32 ); b &= MASK32;
    case 6:  b+=(((unsigned int)p[5] <<  8) & MASK32 ); b &= MASK32;
    case 5:  b+= ((unsigned int)p[4]);                  b &= MASK32;
    case 4:  a+=(((unsigned int)p[3] << 24) & MASK32 ); a &= MASK32;
    case 3:  a+=(((unsigned int)p[2] << 16) & MASK32 ); a &= MASK32;
    case 2:  a+=(((unsigned int)p[1] <<  8) & MASK32 ); a &= MASK32;
    case 1:  a+= ((unsigned int)p[0]);                  a &= MASK32;
    }
    MIX(a, b, c);

    DEBUG && printf( "Hash value is %d.\n", (int)(c) );

    return(c);
}