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factor: improve comments for sieving logic

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Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko
2017-04-13 13:34:40 +02:00
parent a3de0b3b86
commit 021d50405b
1 changed files with 6 additions and 2 deletions
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8
coreutils/factor.c
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@@ -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),