[julia-users] preallocation of dict

[Michele Zaffalon]

Hello,

I am using a dict as a look up table for the result of a computation (it is 
for a Coursera class on cryptography if anybody is wondering):

accum = BigInt(1)
lhs = Dict(accum => 0)
for x1 = 1:2^20-1
    accum = rem(accum * invg, p)
    lhs[accum] = x1
end

and this takes about 20 seconds on my computer. On the other hand, for 
comparison (but not useful for my purpose because I index by the variable 
x1), storing the result in an array of preallocated size is about 2 
seconds. Here is the code:

lhs = Array(Float64, 2^20)
for x1 = 1:2^20-1
    accum = rem(accum * invg, p)
    lhs[x1] = accum
end

Declaring
lhs = Dict{BigInt, Int64}(accum => 0)
does not make any difference.

Is there a way of preallocating the dictionary of a given size?

Thank you,
michele