hash64 generate different value as other language implements

[d3m3vilurr]

similar #27
hash32/64 families generated wrong value (idk reason fingerprint family generated correct value)

for example
python

>>> farmhash.hash64('foo')
6150913649986995171
>>> farmhash.fingerprint64('foo')
6150913649986995171
>>>

farmhash-modern

> x.hash64('foo')
6150913649986995171n
> x.fingerprint64('foo')
6150913649986995171n

but farmhash

> fh.hash64('foo')
'444527491298465133'
> fh.fingerprint64('foo')
'6150913649986995171'

is it bug or do i miss something?

[lovell]

Did you see https://github.com/lovell/farmhash?tab=readme-ov-file#hash ?

The hash methods are platform dependent. Different CPU architectures, for example 32-bit vs 64-bit, Intel vs ARM, SSE4.2 vs AVX might produce different results for a given input.

WebAssembly provides what is essentially a virtual CPU so the hash-based methods will produce a different result from an implementation that can take advantage of SIMD features of a physical CPU.

If you need consistency, please use the fingerprint-based methods.

The fingerprint methods are platform independent, producing the same results for a given input on any machine.

https://github.com/lovell/farmhash?tab=readme-ov-file#fingerprint

[d3m3vilurr]

well...that might be...
I was ignored this possibility that because I tested with manual build python lib & this in same computer.

both projects use cc source code for lib implementation and imo, these cc files are almost same.
only node version made different result.
I'll recheck compile option and others.

[d3m3vilurr]

OK. I got a problem.

first in my case, a input string lengthis 3 (foo).
normal hash function calls NAMESPACE_FOR_HASH_FUNCTIONS::Hash64 and Fingerprint64 uses farmhashna version.

main logic is really same when a length is too small.
(because all HashLen0to16 with <= 3 has same implementation withoutSIMD or CPU accelations)

but still node version call makes differents values.

a main problem is, last step.

#if !defined(FARMHASH_DEBUG) && (!defined(NDEBUG) || defined(_DEBUG))
#define FARMHASH_DEBUG 1
#endif

...

template <typename T> STATIC_INLINE T DebugTweak(T x) {
    if (debug_mode) {
      if (sizeof(x) == 4) {
        x = ~Bswap32(x * c1);
      } else {
        x = ~Bswap64(x * k1);
      }
  }
  return x;
}

...

uint64_t Hash64(const char* s, size_t len) {
  return DebugTweak(
      (can_use_sse42 & x86_64) ?
      farmhashte::Hash64(s, len) :
      farmhashxo::Hash64(s, len))
  );
}

and also (unlike python building), node-gyp never set NDEBUG

so, default suggestiong is correct. differenct cpu can makes different result.
but at least, project have to prevent debug swap :)

diff --git a/binding.gyp b/binding.gyp
index 511a782..f3d3483 100644
--- a/binding.gyp
+++ b/binding.gyp
@@ -25,6 +25,9 @@
         ]
       }]
     ],
+    'defines': [
+      'FARMHASH_DEBUG=0'
+    ],
     'xcode_settings': {
       'CLANG_CXX_LIBRARY': 'libc++',
       'GCC_ENABLE_CPP_EXCEPTIONS': 'YES',

after the patch, result makes same result :)

[lovell]

Ah, great spot about the (lack of) FARMHASH_DEBUG define, that makes sense and I agree we should set this.