This is actually a variant of the Lilius/Clavius algorithm.
I have only reorganised it in an attempt to make it as compact as possible
(for example by moving some constants to other places).
A = year MOD 19
B = year DIV 100
C = (3 x B - 5) DIV 4
D = ( (12 + 11 x A + (8 x B + 13) DIV 25 - C) MOD 30 + 30) MOD 30
if D = 0
or (D = 1
and A > 10)
then E = 56 - D
else E = 57 - D