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-rw-r--r--coreutils/factor.c112
-rwxr-xr-xtestsuite/factor.tests48
2 files changed, 160 insertions, 0 deletions
diff --git a/coreutils/factor.c b/coreutils/factor.c
new file mode 100644
index 0000000..0f838a7
--- /dev/null
+++ b/coreutils/factor.c
@@ -0,0 +1,112 @@
+/*
+ * Copyright (C) 2017 Denys Vlasenko <vda.linux@googlemail.com>
+ *
+ * Licensed under GPLv2, see file LICENSE in this source tree.
+ */
+//config:config FACTOR
+//config: bool "factor"
+//config: default y
+//config: help
+//config: factor factorizes integers
+
+//applet:IF_FACTOR(APPLET(factor, BB_DIR_USR_BIN, BB_SUID_DROP))
+
+//kbuild:lib-$(CONFIG_FACTOR) += factor.o
+
+//usage:#define factor_trivial_usage
+//usage: "NUMBER..."
+//usage:#define factor_full_usage "\n\n"
+//usage: "Print prime factors"
+
+#include "libbb.h"
+
+#if ULLONG_MAX == (UINT_MAX * UINT_MAX + 2 * UINT_MAX)
+/* "unsigned" is half as wide as ullong */
+typedef unsigned half_t;
+#define HALF_FMT ""
+#elif ULLONG_MAX == (ULONG_MAX * ULONG_MAX + 2 * ULONG_MAX)
+/* long is half as wide as ullong */
+typedef unsigned long half_t;
+#define HALF_FMT "l"
+#else
+#error Cant find an integer type which is half as wide as ullong
+#endif
+
+static void factorize(const char *numstr)
+{
+ unsigned long long N, factor2;
+ half_t factor;
+ unsigned count3;
+
+ /* Coreutils compat */
+ numstr = skip_whitespace(numstr);
+ if (*numstr == '+')
+ numstr++;
+
+ N = bb_strtoull(numstr, NULL, 10);
+ if (errno)
+ bb_show_usage();
+
+ printf("%llu:", N);
+
+ if (N < 4)
+ goto end;
+ while (!(N & 1)) {
+ printf(" 2");
+ N >>= 1;
+ }
+
+ count3 = 3;
+ factor = 3;
+ factor2 = 3 * 3;
+ for (;;) {
+ unsigned long long nfactor2;
+
+ while ((N % factor) == 0) {
+ N = N / factor;
+ printf(" %u"HALF_FMT"", factor);
+ }
+ next_factor:
+ /* (f + 2)^2 = f^2 + 4*f + 4 = f^2 + 4*(f+1) */
+ nfactor2 = factor2 + 4 * (factor + 1);
+ if (nfactor2 < factor2) /* overflow? */
+ break;
+ factor2 = nfactor2;
+ if (factor2 > N)
+ break;
+ factor += 2;
+ /* Rudimentary wheel sieving: skip multiples of 3:
+ * Every third odd number is divisible by three and thus isn't a prime:
+ * 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37...
+ * ^ ^ ^ ^ ^ ^ ^ _ ^ ^ _ ^ (^primes)
+ */
+ --count3;
+ if (count3 == 0) {
+ count3 = 3;
+ goto next_factor;
+ }
+ }
+ end:
+ if (N > 1)
+ printf(" %llu", N);
+ bb_putchar('\n');
+}
+
+int factor_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int factor_main(int argc UNUSED_PARAM, char **argv)
+{
+ //// coreutils has undocumented option ---debug (three dashes)
+ //getopt32(argv, "");
+ //argv += optind;
+ argv++;
+
+ if (!*argv)
+ //TODO: read from stdin
+ bb_show_usage();
+
+ do {
+ factorize(*argv);
+ } while (*++argv);
+
+ fflush_stdout_and_exit(EXIT_SUCCESS);
+}
diff --git a/testsuite/factor.tests b/testsuite/factor.tests
new file mode 100755
index 0000000..2cf4a54
--- /dev/null
+++ b/testsuite/factor.tests
@@ -0,0 +1,48 @@
+#!/bin/sh
+
+# Copyright 2017 by Denys Vlasenko <vda.linux@googlemail.com>
+# Licensed under GPLv2, see file LICENSE in this source tree.
+
+. ./testing.sh
+
+# testing "test name" "command" "expected result" "file input" "stdin"
+# file input will be file called "input"
+# test can create a file "actual" instead of writing to stdout
+
+testing "factor ' 0'" \
+ "factor ' 0'" \
+ "0:\n" \
+ "" ""
+testing "factor +1" \
+ "factor +1" \
+ "1:\n" \
+ "" ""
+testing "factor ' +2'" \
+ "factor ' +2'" \
+ "2: 2\n" \
+ "" ""
+
+testing "factor 1024" \
+ "factor 1024" \
+ "1024: 2 2 2 2 2 2 2 2 2 2\n" \
+ "" ""
+
+testing "factor 2^61-1" \
+ "factor 2305843009213693951" \
+ "2305843009213693951: 2305843009213693951\n" \
+ "" ""
+testing "factor 2^62-1" \
+ "factor 4611686018427387903" \
+ "4611686018427387903: 3 715827883 2147483647\n" \
+ "" ""
+testing "factor 2^64-1" \
+ "factor 18446744073709551615" \
+ "18446744073709551615: 3 5 17 257 641 65537 6700417\n" \
+ "" ""
+# This is a 60-bit number (0x888 86ff db34 4692): first few primes multiplied together:
+testing "factor \$((2*3*5*7*11*13*17*19*23*29*31*37*41*43*47))" \
+ "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" \
+ "" ""
+
+exit $FAILCOUNT