Fast vectorizable math functions approximations
- January 26, 2015
- Last updated on 2015/01/27
How and why I designed my own approximated implementations of
log, exp, sin and
cos. The approximation error is quite small, and the
functions are fast and vectorizable. For example, my
logapprox function is 7.5x faster in tight loops than the
icsi_log
function, while being more precise.
Left-recursive versus right-recursive lists in LR parsers
- January 21, 2015
- Last updated on 2015/01/22
Contrary to top-down (LL) parsers, which do not support left recursion, bottom-up (LR) parsers support both left recursion and right recursion. When defining a list-like construct, a user of an LR parser generator, such as Menhir, faces a choice between these two flavors. Which one should she prefer?
Two considerations guide this choice: expressiveness (which flavor leads to fewer conflicts?) and performance (which flavor leads to a more efficient parser?).
In this post, I am mainly interested in discussing expressiveness. I also comment on performance in the setting of Menhir.
As we will see, the bottom line is that neither formulation seems deeply preferable to the other.