factor: new applet
thus far only able to factor up to ULLONG_MAX function old new delta factor_main - 378 +378 packed_usage 31427 31502 +75 applet_names 2590 2597 +7 applet_main 1500 1504 +4 ------------------------------------------------------------------------------ (add/remove: 2/0 grow/shrink: 3/0 up/down: 464/0) Total: 464 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
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Denys Vlasenko
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112
coreutils/factor.c
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112
coreutils/factor.c
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/*
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* Copyright (C) 2017 Denys Vlasenko <vda.linux@googlemail.com>
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*
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* Licensed under GPLv2, see file LICENSE in this source tree.
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*/
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//config:config FACTOR
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//config: bool "factor"
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//config: default y
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//config: help
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//config: factor factorizes integers
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//applet:IF_FACTOR(APPLET(factor, BB_DIR_USR_BIN, BB_SUID_DROP))
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//kbuild:lib-$(CONFIG_FACTOR) += factor.o
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//usage:#define factor_trivial_usage
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//usage: "NUMBER..."
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//usage:#define factor_full_usage "\n\n"
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//usage: "Print prime factors"
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#include "libbb.h"
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#if ULLONG_MAX == (UINT_MAX * UINT_MAX + 2 * UINT_MAX)
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/* "unsigned" is half as wide as ullong */
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typedef unsigned half_t;
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#define HALF_FMT ""
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#elif ULLONG_MAX == (ULONG_MAX * ULONG_MAX + 2 * ULONG_MAX)
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/* long is half as wide as ullong */
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typedef unsigned long half_t;
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#define HALF_FMT "l"
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#else
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#error Cant find an integer type which is half as wide as ullong
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#endif
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static void factorize(const char *numstr)
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{
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unsigned long long N, factor2;
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half_t factor;
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unsigned count3;
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/* Coreutils compat */
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numstr = skip_whitespace(numstr);
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if (*numstr == '+')
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numstr++;
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N = bb_strtoull(numstr, NULL, 10);
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if (errno)
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bb_show_usage();
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printf("%llu:", N);
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if (N < 4)
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goto end;
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while (!(N & 1)) {
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printf(" 2");
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N >>= 1;
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}
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count3 = 3;
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factor = 3;
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factor2 = 3 * 3;
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for (;;) {
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unsigned long long nfactor2;
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while ((N % factor) == 0) {
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N = N / factor;
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printf(" %u"HALF_FMT"", factor);
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}
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next_factor:
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/* (f + 2)^2 = f^2 + 4*f + 4 = f^2 + 4*(f+1) */
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nfactor2 = factor2 + 4 * (factor + 1);
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if (nfactor2 < factor2) /* overflow? */
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break;
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factor2 = nfactor2;
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if (factor2 > N)
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break;
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factor += 2;
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/* Rudimentary wheel sieving: skip multiples of 3:
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* Every third odd number is divisible by three and thus isn't a prime:
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* 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37...
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* ^ ^ ^ ^ ^ ^ ^ _ ^ ^ _ ^ (^primes)
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*/
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--count3;
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if (count3 == 0) {
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count3 = 3;
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goto next_factor;
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}
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}
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end:
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if (N > 1)
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printf(" %llu", N);
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bb_putchar('\n');
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}
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int factor_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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int factor_main(int argc UNUSED_PARAM, char **argv)
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{
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//// coreutils has undocumented option ---debug (three dashes)
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//getopt32(argv, "");
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//argv += optind;
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argv++;
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if (!*argv)
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//TODO: read from stdin
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bb_show_usage();
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do {
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factorize(*argv);
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} while (*++argv);
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fflush_stdout_and_exit(EXIT_SUCCESS);
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}
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48
testsuite/factor.tests
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48
testsuite/factor.tests
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#!/bin/sh
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# Copyright 2017 by Denys Vlasenko <vda.linux@googlemail.com>
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# Licensed under GPLv2, see file LICENSE in this source tree.
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. ./testing.sh
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# testing "test name" "command" "expected result" "file input" "stdin"
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# file input will be file called "input"
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# test can create a file "actual" instead of writing to stdout
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testing "factor ' 0'" \
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"factor ' 0'" \
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"0:\n" \
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"" ""
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testing "factor +1" \
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"factor +1" \
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"1:\n" \
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"" ""
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testing "factor ' +2'" \
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"factor ' +2'" \
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"2: 2\n" \
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"" ""
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testing "factor 1024" \
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"factor 1024" \
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"1024: 2 2 2 2 2 2 2 2 2 2\n" \
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"" ""
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testing "factor 2^61-1" \
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"factor 2305843009213693951" \
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"2305843009213693951: 2305843009213693951\n" \
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"" ""
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testing "factor 2^62-1" \
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"factor 4611686018427387903" \
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"4611686018427387903: 3 715827883 2147483647\n" \
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"" ""
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testing "factor 2^64-1" \
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"factor 18446744073709551615" \
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"18446744073709551615: 3 5 17 257 641 65537 6700417\n" \
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"" ""
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# This is a 60-bit number (0x888 86ff db34 4692): first few primes multiplied together:
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testing "factor \$((2*3*5*7*11*13*17*19*23*29*31*37*41*43*47))" \
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"factor \$((2*3*5*7*11*13*17*19*23*29*31*37*41*43*47))" \
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"614889782588491410: 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47\n" \
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"" ""
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exit $FAILCOUNT
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