Dictionary GetHashCode Inconsistant

i am using this hash for 开发者_Go百科data retrival, but the data retrival is very uniform sometimes i get data under 200 millisecs and sometimes its over a sec.. can any give me some suggestions

public override int GetHashCode()

{

return   
this.DomainID.GetHashCode() *(851) *    
(this.A.HasValue ? this.A.GetHashCode() : 1) * (851) *    
((this.C != null ? this.C.ToLower().GetHashCode() : 1)^     
(this.Ap != null ? this.Ap.ToLower().GetHashCode() : 1) * (851) *    
(this.Ks != null ? this.Ks.ToLower().GetHashCode() : 1)) *  
(this.Le != null ? Le.ToLower().GetHashCode() : 1);

}

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The code itself looks alright at a first glance, but there is a lot of things that we don't see. What types are DomainID, A, C, Ap, Ks and Le for example? And how are their GetHashCode-methods implemented?

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It might suggest that one of your conditions is slower than the rest. Maybe the ToLower() is an expensive call dependant on which values in the the this are null