For block sizes less than BLOCK_SIZE1, always use the serial algorithm.
For block sizes less than BLOCK_SIZE1, always use the serial algorithm.

A block is generally too small for threading to be an advantage.

pombredanne/numexpr,robbmcleod/numexpr,andreabedini/numexpr,robbmcleod/numexpr,andreabedini/numexpr,pydata/numexpr,andreabedini/numexpr,pydata/numexpr,pombredanne/numexpr,pydata/numexpr,pombredanne/numexpr,robbmcleod/numexpr