4 ms·

Agreed, I think the real lesson is: reading is 10x cheaper than branching, so if you can do something with 10 non-branching ops it'll be just as fast as a singl

• seabee 14y ago
  Conversely: if you can do something with a branch that's correctly predicted 90% of the time it'll be just as fast as 10 non-branching ops. Branch prediction is a tool like any other - don't neglect it when it can help you.
  • marshray 14y ago
    As a coder, how can I predict the branch predictor?
    • CamperBob2 14y ago
      There are definite rules, documented by the CPU vendor. A forward branch is assumed not taken, while a backward branch is assumed to come at the end of a loop that will probably iterate more than once. See http://software.intel.com/en-us/articles/branch-and-loop-reorganization-to-prevent-mispredicts/ http://software.intel.com/en-us/articles/branch-and-loop-reo... for example. I'd assume the particulars will vary between CPU manufacturers and families, but the idea that backward branches will probably be taken seems fairly universal.
      • haberman 14y ago
        This is outdated information; Intel chips have not used static prediction for conditional branches since NetBurst (Pentium 4). "Pentium M, Intel Core Solo and Intel Core Duo processors do not statically predict conditional branches according to the jump direction. All conditional branches are dynamically predicted, even at first appearance." --http://www.intel.com/content/dam/doc/manual/64-ia-32-architectures-optimization-manual.pdf http://www.intel.com/content/dam/doc/manual/64-ia-32-archite...