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factor: detect squares

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If we have a square, the speedup can be extremely large
(in best case example below, it's ~40000 times faster):

$ time ./busybox_old factor 18446743988964486098
18446743988964486098: 2 3037000493 3037000493
real	0m4.246s
$ time ./busybox factor 18446743988964486098
18446743988964486098: 2 3037000493 3037000493
real	0m0.000s

function                                             old     new   delta
isqrt_odd                                              -      57     +57
print_w                                                -      36     +36
factorize                                            218     236     +18
print_h                                                -       7      +7
factorize_numstr                                      65      72      +7
------------------------------------------------------------------------------
(add/remove: 3/0 grow/shrink: 2/0 up/down: 125/0)             Total: 125 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko
2020-12-22 20:08:40 +01:00
parent 96717d9fb4
commit 6452c30036
2 changed files with 62 additions and 3 deletions
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23
testsuite/factor.tests
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@@ -45,4 +45,27 @@ testing "factor \$((2*3*5*7*11*13*17*19*23*29*31*37*41*43*47))" \
"614889782588491410: 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47\n" \
"" ""
# Test that square-detection code is not buggy
testing "factor 2 * 3037000493 * 3037000493" \
"factor 18446743988964486098" \
"18446743988964486098: 2 3037000493 3037000493\n" \
"" ""
testing "factor 3 * 2479700513 * 2479700513" \
"factor 18446743902517389507" \
"18446743902517389507: 3 2479700513 2479700513\n" \
"" ""
# including square-of-square cases:
testing "factor 3 * 37831 * 37831 * 37831 * 37831" \
"factor 6144867742934288163" \
"6144867742934288163: 3 37831 37831 37831 37831\n" \
"" ""
testing "factor 3 * 13^16" \
"factor 1996249827549539523" \
"1996249827549539523: 3 13 13 13 13 13 13 13 13 13 13 13 13 13 13 13 13\n" \
"" ""
testing "factor 13^16" \
"factor 665416609183179841" \
"665416609183179841: 13 13 13 13 13 13 13 13 13 13 13 13 13 13 13 13\n" \
"" ""
exit $FAILCOUNT