5 ms·
Btw, XOR swap... probably slower than register-aliased swap, but it swaps two registers without using a third: void swap(char *s, int a, int b) {
by swingline-747 8y ago
Btw, XOR swap...
probably slower than register-aliased swap, but it swaps two registers without using a third:
void swap(char *s, int a, int b)
{
s[b] ^= s[a];
s[a] ^= s[b];
s[b] ^= s[a];
}
- ur-whale 8y agoYou'd better hope that a!=b
- scj 8y agoWhy would a==b be a problem with the XOR swap trick? function xorSwapTest(min, max) { for (var i = min; i < max; i++) { var a = i, b = i; b ^= a; a ^= b; b ^= a; if (a != i || b != i) throw Error("Problem with " + i); } return true; }
- saagarjha 8y agoThe issue is that if a == b, &s[a] == &s[b]; i.e. you're writing to the same address.
- and-then 8y agoEdge-case FUD.
- saagarjha 8y agoMost compilers will optimize this to whatever is faster even if you use the clearer version.
- and-then 8y agoYou're making a sweeping, laughably-false assertion. Clearly you don't understand how compilers work. C compilers are not miraculous magic boxes. They have limited information and limited optimizations. It's very likely an obscure implementation of an algorithm will more-or-less translate one-to-one to nearly equivalent assembly because the compiler can't analyze it.
- saagarjha 8y agoI think you've misrepresented what I said, which was that the compiler is good enough to pick between a register or XOR-swap (in the comment I was replying to), based on the architecture and calling sites.
- foota 8y agoThe "Clearly you don't understand how compilers work" portion of this comment is unnecessary.