There is a performance difference, especially for enter. On modern processors this decodes to some 10 to 20 µops, while the three instruction sequence is about 4 to 6, depending on the architecture. For details consult Agner Fog’s instruction tables. Additionally the enter instruction usually has a quite high latency, for example 8 clocks on … Read more
When you get down to the lowest level (machine code but I’ll use assembly since it maps one-to-one mostly), the difference between an empty loop decrementing to 0 and one incrementing to 50 (for example) is often along the lines of: ld a,50 ld a,0 loop: dec a loop: inc a jnz loop cmp a,50 … Read more
Use the operation that best describes what you are trying to do. If you are treating the number as a sequence of bits, use bitshift. If you are treating it as a numerical value, use division. Note that they are not exactly equivalent. They can give different results for negative integers. For example: -5 / … Read more
It is pretty well known that static inline int is_odd_A(int x) { return x & 1; } is more efficient than static inline int is_odd_B(int x) { return x % 2; } But with the optimizer on, will is_odd_B be no different from is_odd_A? No — with gcc-4.2 -O2, we get, (in ARM assembly): _is_odd_A: … Read more