#include // Assembly: https://godbolt.org/z/mFLtHY #include // Q&A: https://www.sololearn.com/Discuss/1565316/?ref=app #include #include // fast32, normal and least32 // INPUT: enter an integer up to around 75000000 (75 million) int main() { uint_fast32_t fast = 0; uint32_t normal = 0; uint_least32_t least = 0; clock_t starts[3], stops[3]; // To see types reported by compiler, use %d in printf's below // and use srandom() to force an error dump ("long long unsigned int") srand(time(NULL)); uint32_t iters; printf("iters: "); scanf("%d", &iters); starts[0] = clock(); for(int i=0; i> 15); fast = fast ^ (fast << 4); // QWORD PTR } stops[0] = clock(); starts[1]=clock(); for(int i=0; i> 15); normal = normal ^ (normal << 4); // DWORD PTR } stops[1] = clock(); starts[2] = clock(); for(int i=0; i> 15); least = least ^ (least << 4); // DWORD PTR } stops[2] = clock(); // 8 4 4 on my 64-bit system (QWORD, like GodBolt) // 4 4 4 here (DWORDs) printf("Sizes %I64d %I64d %I64d\n", sizeof(fast), sizeof(normal), sizeof(least)); // Without this, -O1 omits the loops completely printf("Values: %I64d %I64d %I64d\n", fast, normal, least); printf("Times: %.2f %.2f %.2f", (double)stops[0]-starts[0], (double)stops[1]-starts[1], (double)stops[2]-starts[2]); return 0; } /* godbolt.org (using additions) -O0 fast: add QWORD PTR [rbp-8], rax ; 64-bit register normal: add DWORD PTR [rbp-12], eax ; 32-bit least: add DWORD PTR [rbp-16], eax ; 32-bit -O1, -O2, -O3 fast: add rbp, rax ; both 64-bit, see LEA note normal: add r12d, eax ; both 32-bit least: add r13d, eax ; both 32-bit Note that on optimization levels 1+, the compiler would sometimes choose LEA instead of ADD. That was rare (it's consistent / all the same in this code) */

Type timing: fast32, normal and least32