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Groups.jl
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slightly more performant version of power_by_squaring

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kalmar 2017-01-31 14:53:41 +01:00
parent 0882b740d3
commit 9e435188e1
1 changed files with 6 additions and 5 deletions
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src/Groups.jl
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@ -158,21 +158,22 @@ function power_by_squaring{T}(x::GWord{T}, p::Integer)
elseif p == 2 elseif p == 2
return x*x return x*x
end end
x = deepcopy(x)
t = trailing_zeros(p) + 1 t = trailing_zeros(p) + 1
p >>= t p >>= t
while (t -= 1) > 0 while (t -= 1) > 0
x *= x r_multiply!(x, x.symbols)
end end
y = x y = deepcopy(x)
while p > 0 while p > 0
t = trailing_zeros(p) + 1 t = trailing_zeros(p) + 1
p >>= t p >>= t
while (t -= 1) >= 0 while (t -= 1) >= 0
x *= x r_multiply!(x, x.symbols)
end end
y *= x r_multiply!(y, x.symbols)
end end
return freegroup_reduce!(y) return Groups.freegroup_reduce!(y)
end end
(^)(x::GWord, n::Integer) = power_by_squaring(x,n) (^)(x::GWord, n::Integer) = power_by_squaring(x,n)