Can someone explain USE_LEFT in pp.h?

Can anyone explain to me just what the USE_LEFT macro in pp.h
accomplishes?  It seems to only be used (in the core anyway) by
pp_add, pp_subtract, pp_bit_or, and pp_bit_xor.

• Can someone explain USE_LEFT in pp.h? by sthoenna
• Re: Can someone explain USE_LEFT in pp.h? by Jarkko Hietaniemi
• Re: Can someone explain USE_LEFT in pp.h? by sthoenna
• Re: Can someone explain USE_LEFT in pp.h? by Jarkko Hietaniemi