5 ms·

All those if statements inside loops... would be a lot cleaner (and faster!) to just use a single goto statement: goto cont; for (; ; ++z) for (; x <=

by zwegner 12y ago

All those if statements inside loops... would be a lot cleaner (and faster!) to just use a single goto statement: goto cont; for (; ; ++z) for (; x <= z; ++x) for (; y <= z; ++y) { if (x*x + y*y == z*z) return *this; cont: }

jzwinck 12y ago
I totally agree--thank you for bringing this up. I'm not sure it would be faster, but it is an interesting case for goto. I saw another proposal referencing the original article which used a trio of functions in a nice way to achieve something similar without the goto (and without the ifs). My main point was to illustrate the use of custom iterators.
- zwegner 12y ago
  Consider me nerd-sniped. I typed the last post on my phone, but just had to bust out the laptop to check. Noticed a couple bugs I had: the for-loop initializers need to be set, and there needs to be an empty statement after the cont: label. The goto version only has one unconditional branch outside of a loop, rather than three conditional branches inside loops. Anyways, the speed difference shouldn't be too big, as the branches are pretty predictable (pretty much always not taken). Quick benchmark of the original and mine, up to the first 3000 triples: $ c++ -O3 pyth1.cpp && time ./a.out | md5 33aa33d6cad59951489757e06aeb5a15 real 0m5.492s user 0m5.484s sys 0m0.007s $ c++ -O3 pyth2.cpp && time ./a.out | md5 33aa33d6cad59951489757e06aeb5a15 real 0m4.248s user 0m4.238s sys 0m0.011s
5hoom 12y ago
I'm always looking for a legitimate excuse to use a goto in my C++ code because I'm perverse. It's very rare to find one but this looks like it might be okay.
Pxtl 12y ago
All the crazy crap they added to C/C++, how was named loops and corresponding named break/continue not one of them?
- tspiteri 12y ago
  In this case, the goto is into the loop, not out of it, so named break/continue would not help. And the only point of having named break/continue would be to not use goto. I don't see the point in that, since to me, this: for (i = 0; i < ie; i++) { continue_i: for (j = 0; j < je; j++) { if (cond1) goto break_i; if (cond2) goto continue_i; /* ... */ } } break_i: is as readable as this: loop_i: for (i = 0; i < ie; i++) { for (j = 0; j < je; j++) { if (cond1) break loop_i; if (cond2) continue loop_i; /* ... */ } }
deleted 12y ago
[deleted]

by zwegner 12y ago

jzwinck 12y ago

I totally agree--thank you for bringing this up. I'm not sure it would be faster, but it is an interesting case for goto. I saw another proposal referencing the original article which used a trio of functions in a nice way to achieve something similar without the goto (and without the ifs). My main point was to illustrate the use of custom iterators.

zwegner 12y ago
Consider me nerd-sniped. I typed the last post on my phone, but just had to bust out the laptop to check. Noticed a couple bugs I had: the for-loop initializers need to be set, and there needs to be an empty statement after the cont: label. The goto version only has one unconditional branch outside of a loop, rather than three conditional branches inside loops. Anyways, the speed difference shouldn't be too big, as the branches are pretty predictable (pretty much always not taken). Quick benchmark of the original and mine, up to the first 3000 triples: $ c++ -O3 pyth1.cpp && time ./a.out | md5 33aa33d6cad59951489757e06aeb5a15 real 0m5.492s user 0m5.484s sys 0m0.007s $ c++ -O3 pyth2.cpp && time ./a.out | md5 33aa33d6cad59951489757e06aeb5a15 real 0m4.248s user 0m4.238s sys 0m0.011s

5hoom 12y ago

I'm always looking for a legitimate excuse to use a goto in my C++ code because I'm perverse. It's very rare to find one but this looks like it might be okay.

Pxtl 12y ago

All the crazy crap they added to C/C++, how was named loops and corresponding named break/continue not one of them?

tspiteri 12y ago
In this case, the goto is into the loop, not out of it, so named break/continue would not help. And the only point of having named break/continue would be to not use goto. I don't see the point in that, since to me, this: for (i = 0; i < ie; i++) { continue_i: for (j = 0; j < je; j++) { if (cond1) goto break_i; if (cond2) goto continue_i; /* ... */ } } break_i: is as readable as this: loop_i: for (i = 0; i < ie; i++) { for (j = 0; j < je; j++) { if (cond1) break loop_i; if (cond2) continue loop_i; /* ... */ } }

deleted 12y ago

[deleted]