factor: improve comments for sieving logic

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

diff --git a/coreutils/factor.c b/coreutils/factor.c
index 7adc2385af9b7954d9e187b92896605923c450bb..5e23c6ca70446d19d02138adccdb6ebc7777f1a4 100644 (file)
--- 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),