hash in SGObject

[yorkerlin]

@vigsterkr , @lisitsyn , @karlnapf
there may be a bug.
If CSGObject::update_parameter_hash() is called more than once, CSGObject::parameter_hash_changed() always returns true even when variables remain the same.

for example

void CExactInferenceMethod::update()
{

    CInferenceMethod::update();
    update_chol();
    update_alpha();
    update_deriv();
    update_mean();
    update_cov();

    update_parameter_hash();
    SG_SPRINT("hash value1 %d \n", m_hash);  
    update_parameter_hash();
    SG_SPRINT("hash value2 %d \n", m_hash);  

}

hash value1 and hash value2 are different since

void CSGObject::update_parameter_hash()
{
    uint32_t carry=0;
    uint32_t length=0;

    get_parameter_incremental_hash(m_hash, carry, length); 
    m_hash=CHash::FinalizeIncrementalMurmurHash3(m_hash, carry, length);
}

where m_hash becomes non-zero after update_parameter_hash() is called

what is worse,

bool CSGObject::parameter_hash_changed()
{
    uint32_t hash=0;
    uint32_t carry=0;
    uint32_t length=0;

    get_parameter_incremental_hash(hash, carry, length); 
    hash=CHash::FinalizeIncrementalMurmurHash3(hash, carry, length);

    return (m_hash!=hash);
}

Note that hash is zero, which means if update_parameter_hash() is called more than once, CSGObject::parameter_hash_changed() always returns true even when variables remain the same.

[yorkerlin]

I am not sure whether the hash value should be changed if parameter_hash_changed() is called even when values of variables in the object remain unchanged

[yorkerlin]

if you think this is a bug, the fix is quite simple.

void CSGObject::update_parameter_hash()
{
    uint32_t carry=0;
    uint32_t length=0;

    //CHANGE m_hash to 0
    get_parameter_incremental_hash(0, carry, length);  
    m_hash=CHash::FinalizeIncrementalMurmurHash3(m_hash, carry, length);
}

[karlnapf]

I think this is a bug! This should not be. Do unit tests break if you fix it?
Make sure to add unit tests for the hashing if you do fix it
Thanks!

[yorkerlin]

this issue is solved.
I close this