7e5f2f3b5
Denys Vlasenko
2017-04-09
Subject
factor: expand comments
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coreutils/factor.c+7 -4
| @@ -107,9 +107,12 @@ static NOINLINE void factorize(wide_t N) | |
| factor = 3; | |
| factor2 = 3 * 3; | |
| for (;;) { | |
| - | while ((N % factor) == 0) { |
| + | /* The division is the most costly part of the loop. |
| + | * On 64bit CPUs, takes at best 12 cycles, often ~20. |
| + | */ |
| + | while ((N % factor) == 0) { /* not likely */ |
| N = N / factor; | |
| - | printf(" %u"HALF_FMT"", factor); |
| + | printf(" %u"HALF_FMT, factor); |
| max_factor = isqrt_odd(N); | |
| } | |
| next_factor: | |
| @@ -122,8 +125,8 @@ static NOINLINE void factorize(wide_t N) | |
| factor += 2; | |
| /* Rudimentary wheel sieving: skip multiples of 3: | |
| * Every third odd number is divisible by three and thus isn't a prime: | |
| - | * 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37... |
| - | * ^ ^ ^ ^ ^ ^ ^ _ ^ ^ _ ^ |
| + | * 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47... |
| + | * ^ ^ ^ ^ ^ ^ ^ _ ^ ^ _ ^ ^ ^ ^ |
| * (^ = primes, _ = would-be-primes-if-not-divisible-by-5) | |
| */ | |
| --count3; | |