Update: the Efficiency cores on Alder Lake are Gracemont, and run inc reg as a single uop, but at only 1/clock, vs. 4/clock for add reg, 1 (https://uops.info/). This may be a false dependency on FLAGS like P4 had; the uops.info tests didn’t try adding a dep-breaking instruction. Other than the TL:DR, I haven’t updated … Read more
i += Increment(ref i); is equivalent to i = i + Increment(ref i); The expression on the right hand side of the assignment is evaluated from left to right, so the next step is i = 0 + Increment(ref i); return i++ returns the current value of i (which is 0), then increments i i … Read more
No, this code is absolutely, demonstrably not threadsafe. import threading i = 0 def test(): global i for x in range(100000): i += 1 threads = [threading.Thread(target=test) for t in range(10)] for t in threads: t.start() for t in threads: t.join() assert i == 1000000, i fails consistently. i += 1 resolves to four opcodes: … Read more
My guess is this was omitted because it would only work for mutable variables, and it would not make sense for immutable values. Perhaps it was decided that the ++ operator doesn’t scream assignment, so including it may lead to mistakes with regard to whether or not you are mutating the variable. I feel that … Read more
In both C and C++, the result of x++ is an rvalue, so you can’t assign to it. In C, ++x is equivalent to x += 1 (C standard ยง6.5.3.1/p2; all C standard cites are to WG14 N1570). In C++, ++x is equivalent to x += 1 if x is not a bool (C++ standard … Read more
The ++ has equal precedence with the * and the associativity is right-to-left. See here. It’s made even more complex because even though the ++ will be associated with the pointer the increment is applied after the statement’s evaluation. The order things happen is: Post increment, remember the post-incremented pointer address value as a temporary … Read more
It comes from the history of using integer values as booleans. If x is an int, but I am using it as a boolean as per if(x)… then incrementing will mean that whatever its truth value before the operation, it will have a truth-value of true after it (barring overflow). However, it’s impossible to predict … Read more
tldr; Although both var++ and ++var increment the variable they are applied to, the result returned by var++ is the value of the variable before incrementing, whereas the result returned by ++var is the value of the variable after the increment is applied. Further Explanation When ++var or var++ form a complete statement (as in … Read more
It’s just a rule, that’s all, and is possibly there to (1) make it easier to write C compilers and (2) nobody has convinced the C standards committee to relax it. Informally speaking you can only write ++foo if foo can appear on the left hand side of an assignment expression like foo = bar. … Read more
In Python 2.x, just use the ord and chr functions: >>> ord(‘c’) 99 >>> ord(‘c’) + 1 100 >>> chr(ord(‘c’) + 1) ‘d’ >>> Python 3.x makes this more organized and interesting, due to its clear distinction between bytes and unicode. By default, a “string” is unicode, so the above works (ord receives Unicode chars … Read more