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authorDenys Vlasenko2017-04-09 23:12:38 +0200
committerDenys Vlasenko2017-04-09 23:12:38 +0200
commit7e5f2f3b5163a3c7c6b20a311f1177f9c4f04b81 (patch)
tree7f3b277b887c0a841120eac95db964f6ac63c5c6
parent1d232fd44026deae94c88200766152aec9d6c5e5 (diff)
downloadbusybox-7e5f2f3b5163a3c7c6b20a311f1177f9c4f04b81.zip
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factor: expand comments
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
-rw-r--r--coreutils/factor.c11
1 files changed, 7 insertions, 4 deletions
diff --git a/coreutils/factor.c b/coreutils/factor.c
index e011901..1c01e3f 100644
--- a/coreutils/factor.c
+++ b/coreutils/factor.c
@@ -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;