Can you help me to find the best way to calculate hashcode for the class that has 3 int params (let say a, b, c) and each param may have values in the predefined range? I mean that a should be in some range from a1 to a2, b correspondingly from b1 to b2 and c as you may guess from c1 to c2. All these a1, a2, b1... are constant and known when the hashcode builds. I wish to avoid collisions.
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1Well if the three ranges end up with more than 2^32 possible values, it's impossible to avoid collisions. What *are* the ranges? – Jon Skeet Jun 10 '18 at 13:31
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assuming that the product of ranges does not exceed Integer.MAX_VALUE – Bizon4ik Jun 10 '18 at 14:26
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First of all, make sure that total number of variants - product (a2 - a1) * (b2 - b1) * (c2 - c1) fits into your hashcode capacity. If you are going to use 32-bit unsigned int, that value should be less than 2^32.
Start constructing hashcode by picking some initial value s (you can pick zero thus effectively omitting the initial value). Then for each param do the following:
- Multiply current hashcode value by current param range (i.e.
a2 - a1) - Add current adjusted to range param value to the hashcode value
For your case of three params the formula is
((s*(a2 - a1) + (a - a1))*(b2 - b1) + (b - b1))*(c2 - c1) + (c - c1)
where s is optional starting value
EDIT
Param value added should be adjusted to its range
Vasily Liaskovsky
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