factor: expand comments

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 7 insertions, 4 deletions

diff --git a/coreutils/factor.c b/coreutils/factor.c
index e01190150..1c01e3f27 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;