better vectorized definitions

base/abstractarray.jl

@@ -994,7 +994,7 @@ function repmat(a::AbstractVector, m::Int)
 end
 
 sub2ind(dims::Tuple{}) = 1
-sub2ind(dims::Tuple{},i1::Integer, I::Integer...) = i1==1 ? sub2ind(dims,I...) : throw(BoundsError())
+sub2ind(dims::Tuple{},I::Integer...) = sum(I) - length(I) + 1
 sub2ind(dims::Tuple{Integer,Vararg{Integer}}, i1::Integer) = i1
 sub2ind(dims::Tuple{Integer,Vararg{Integer}}, i1::Integer, I::Integer...) = i1 + dims[1]*(sub2ind(tail(dims),I...)-1)
 
@@ -1010,20 +1010,38 @@ end
 ind2sub(a::AbstractArray, ind::Integer) = ind2sub(size(a), ind)
 # sub2ind(a::AbstractArray, I::Integer...) = sub2ind(size(a), I...)
 
-sub2ind{T<:Integer}(dims::Tuple{Vararg{Integer}}, I::AbstractVector{T}...) =
-    [ sub2ind(dims, map(X->X[i], I)...)::Int for i=1:length(I[1]) ]
+function sub2ind{T<:Integer}(dims::Tuple{Vararg{Integer}}, I::AbstractVector{T}...)
+    N = length(dims)
+    M = length(I[1])
+    indices = copy(I[1])
+
+    s = dims[1]
+    for j=2:length(I)
+        Ij = I[j]
+        for i=1:M
+            indices[i] += s*(Ij[i]-1)
+        end
+        s*= (j <= N ? dims[j] : 1)
+    end
+    return indices
+end
 
 function ind2sub{T<:Integer}(dims::Tuple{Vararg{Integer}}, ind::AbstractVector{T})
-    n = length(dims)
-    l = length(ind)
-    t = ntuple(n, x->Array(Int, l))
-    for i = 1:l
-        s = ind2sub(dims, ind[i])
-        for j = 1:n
-            t[j][i] = s[j]
+    N = length(dims)
+    M = length(ind)
+    t = [Array{T}(M) for j=1:N]
+    copy!(t[1],ind)
+    for j = 1:N-1
+        d = dims[j]
+        tj = t[j]
+        tj2 = t[j+1]
+        for i = 1:M
+            ind2 = div(tj[i]-1, d)
+            tj[i] -= d*ind2
+            tj2[i] = ind2+1
         end
     end
-    return t
+    return tuple(t...)
 end
 
 function ind2sub!{T<:Integer}(sub::Array{T}, dims::Tuple{Vararg{T}}, ind::T)