Filling an array

["Pavel A. Romashkin" <pavel.romashkin(at)noaa.gov>]

If I have

a = findgen(10)
b = fix(100* randomu(10, 10))
; N_elements(a) is equal to n_elements(b)
c = findgen(total(b))

how can I fill C with values from A using B as a running index, so that

c[0 : b[0]-1] = a[0]
c[b[0] : b[0]+b[1]-1] = a[1]

etc, without looping through "n_elements(b)-1" iterations?
I have a fast solution with a loop and indexing using total(/cumulative)
and a very slow one with loop and replicate, but I can't come up with a
loop-free one.

Thank you,
Pavel