diff options
| author | Denys Vlasenko <vda.linux@googlemail.com> | 2017-04-13 13:34:40 +0200 |
|---|---|---|
| committer | Denys Vlasenko <vda.linux@googlemail.com> | 2017-04-13 13:34:40 +0200 |
| commit | 021d50405b5819df9e86a3f1354e45018885517e (patch) | |
| tree | 1c47f569cd6bc2f165b183cde987d50907f1683b /coreutils/factor.c | |
| parent | a3de0b3b86deb37c2adc993c6357c1a31b7ecb5b (diff) | |
| download | busybox-021d50405b5819df9e86a3f1354e45018885517e.tar.gz | |
factor: improve comments for sieving logic
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Diffstat (limited to 'coreutils/factor.c')
| -rw-r--r-- | coreutils/factor.c | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/coreutils/factor.c b/coreutils/factor.c index 7adc2385a..5e23c6ca7 100644 --- a/coreutils/factor.c +++ b/coreutils/factor.c @@ -73,7 +73,7 @@ static NOINLINE void factorize(wide_t N) MULTIPLE_OF_3 = 1 << 2, MULTIPLE_OF_5 = 1 << 6, MULTIPLE_OF_7 = 1 << 11, - MULTIPLE_3_5_7 = MULTIPLE_OF_3 | MULTIPLE_OF_5 | MULTIPLE_OF_7, + MULTIPLE_DETECTED = MULTIPLE_OF_3 | MULTIPLE_OF_5 | MULTIPLE_OF_7, }; unsigned sieve_word; @@ -102,9 +102,13 @@ static NOINLINE void factorize(wide_t N) // count5 = 6; // count7 = 9; sieve_word = 0 + /* initial count for SHIFT_n is (n-1)/2*3: */ + (MULTIPLE_OF_3 - 3 * SHIFT_3) + (MULTIPLE_OF_5 - 6 * SHIFT_5) + (MULTIPLE_OF_7 - 9 * SHIFT_7) + //+ (MULTIPLE_OF_11 - 15 * SHIFT_11) + //+ (MULTIPLE_OF_11 - 18 * SHIFT_13) + //+ (MULTIPLE_OF_11 - 24 * SHIFT_17) ; factor = 3; for (;;) { @@ -133,7 +137,7 @@ static NOINLINE void factorize(wide_t N) // if (count3 && count5 && count7) // continue; sieve_word += INCREMENT_EACH; - if (!(sieve_word & MULTIPLE_3_5_7)) + if (!(sieve_word & MULTIPLE_DETECTED)) continue; /* * "factor" is multiple of 3 33% of the time (count3 reached 0), |