Re: How should unordered_map be used correctly ... ?

James Kanze <>
Tue, 21 Dec 2010 01:21:39 -0800 (PST)
On Dec 20, 10:01 pm, mast4as <> wrote:


You said the hash function I was using isn't good but that's the one
they use in the paper i am following.

I said it's not good in general. It may be perfectly adequate
for the set of values you will probably encounter. (And
creating a truly good hash function for float or double, which
will be effective for almost any set of input, is extremely

I am converting the particles
positions (floating point) into discrete coordinates (grid cell
positions) so at the end my x, y, z values for the hash function are

As for the 256 sorry to show maybe a big hole in my knowledge here but
I assumed that a size_t could only encode 256 values (8 bits). I am
probably mistaken so if you can shred some light on this I would be
more than happy. I want to understand ;-)

According to the standard, size_t is a typedef to an unsigned
integral type large enough to contain the size of the largest
possible object. On most systems (probably all modern systems),
it is the same size as a pointer.

James Kanze

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