Measure the cost of a 64-bit divide. Divides don't take a constant number of cycles. Values were chosen here semi-randomly to depict a fairly expensive scenario. Someone with fancy ALU knowledge could probably pick worse values.
| 446 | // fairly expensive scenario. Someone with fancy ALU knowledge could |
| 447 | // probably pick worse values. |
| 448 | double div64() |
| 449 | { |
| 450 | int count = 1000000; |
| 451 | // NB: Expect an x86 processor exception is there's overflow. |
| 452 | uint64_t start = Cycles::rdtsc(); |
| 453 | uint64_t numeratorHi = 0x5a5a5a5a5a5UL; |
| 454 | uint64_t numeratorLo = 0x55aa55aa55aa55aaUL; |
| 455 | uint64_t divisor = 0xaa55aa55aa55aa55UL; |
| 456 | uint64_t quotient; |
| 457 | uint64_t remainder; |
| 458 | for (int i = 0; i < count; i++) { |
| 459 | __asm__ __volatile__("divq %4" : |
| 460 | "=a"(quotient), "=d"(remainder) : |
| 461 | "a"(numeratorLo), "d"(numeratorHi), "r"(divisor) : |
| 462 | "cc"); |
| 463 | } |
| 464 | uint64_t stop = Cycles::rdtsc(); |
| 465 | return Cycles::toSeconds(stop - start)/count; |
| 466 | } |
| 467 | |
| 468 | // Measure the cost of calling a non-inlined function. |
| 469 | double functionCall() |