Why is Math.DivRem so inefficient?

Question

In my computer this code takes 17 seconds (1000 millions times):

static void Main(string[] args) {
   var sw = new Stopwatch(); sw.Start();
   int r;
   for          


        

Answer 1

If I had to take a wild guess, I'd say that whoever implemented Math.DivRem had no idea that x86 processors are capable of doing it in a single instruction, so they wrote it as two operations. That's not necessarily a bad thing if the optimizer works correctly, though it is yet another indicator that low-level knowledge is sadly lacking in most programmers nowadays. I would expect the optimizer to collapse modulus and then divide operations into one instruction, and the people who write optimizers should know these sorts of low-level things...