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>

diff --git a/coreutils/factor.c b/coreutils/factor.c
new file mode 100644 (file)
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 (executable)
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