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(factor): Rewrite inner loop to be more efficient.

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Patch from Torbjorn Granlund.
This commit is contained in:
Jim Meyering
1997-02-20 05:11:12 +00:00
parent 9e2c86c67a
commit 2e31651a02
1 changed files with 11 additions and 7 deletions
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18
src/factor.c
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@@ -20,7 +20,6 @@
#include <config.h>
#include <stdio.h>
#include <math.h>
#include <sys/types.h>
#include <assert.h>
@@ -86,9 +85,8 @@ Print factors of each NUMBER; read standard input with no arguments.\n\
static int
factor (long unsigned int n0, int max_n_factors, long unsigned int *factors)
{
register unsigned long n = n0, d;
register unsigned long n = n0, d, q;
int n_factors = 0;
unsigned int sqrt_n;
if (n < 1)
return n_factors;
@@ -107,16 +105,22 @@ factor (long unsigned int n0, int max_n_factors, long unsigned int *factors)
(3) n is composite but has no factors less than d.
If (1) or (2) obviously the right thing happens.
If (3), then since n is composite it is >= d^2. */
sqrt_n = (unsigned int) sqrt ((double) n);
for (d = 3; d <= sqrt_n; d += 2)
d = 3;
do
{
while (n % d == 0)
q = n / d;
while (n == q * d)
{
assert (n_factors < max_n_factors);
factors[n_factors++] = d;
n /= d;
n = q;
q = n / d;
}
d += 2;
}
while (d <= q);
if (n != 1 || n0 == 1)
{
assert (n_factors < max_n_factors);