Working on a Finite element solver for the fun of it, I encountered a math problem where the area of a triangle has to be solved multiple times for different triangular elements on a mesh. Note: This is all being done in Cython: For the 2D case, the determinant formula allows us to do this by the least number of arithmetic operations. A = 0.5|[x_1(y_2-y_3) + x_2(y_3-y_1) + x_3(y_1-y_2)]| However this will be called once for each element and, in the case of adaptive meshing, for every iteration too. So finding the absolute value becomes a problem. Going with a function that does comparisons and if-else branching seems wrong. So i thought that bit manipulation could be a solution here maybe and went with this approach. from libc.stdint cimport uint64_t cdef union DoubleIntUnion: double double_nr uint64_t int_nr cdef double fastABS(double number) nogil: cdef DoubleIntUnion u_number u_number.double_nr = number u_number.int_nr &= <uint64_t>0x7FFFFFFFFFFFFFFF return u_number.double_nr this works. But is there any way to do it better in this case or any suggestions ? Continue reading...
