X-Git-Url: https://git.librecmc.org/?a=blobdiff_plain;ds=sidebyside;f=coreutils%2Ffactor.c;h=467e23a4d81aebbda0fcba7cab6f31d05f14c0d8;hb=00bd76728d44901a260f2dcdbeed52b3c85d6b6b;hp=11097c12de046ff0080ab38c4b446c045e9204b2;hpb=cc1f8ba489b809d2c859276ef10094df4bcc74ea;p=oweals%2Fbusybox.git diff --git a/coreutils/factor.c b/coreutils/factor.c index 11097c12d..467e23a4d 100644 --- a/coreutils/factor.c +++ b/coreutils/factor.c @@ -4,17 +4,17 @@ * Licensed under GPLv2, see file LICENSE in this source tree. */ //config:config FACTOR -//config: bool "factor" +//config: bool "factor (2.6 kb)" //config: default y //config: help -//config: factor factorizes integers +//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: "[NUMBER]..." //usage:#define factor_full_usage "\n\n" //usage: "Print prime factors" @@ -27,8 +27,6 @@ #endif typedef unsigned long long wide_t; -#define WIDE_BITS (unsigned)(sizeof(wide_t)*8) -#define TOPMOST_WIDE_BIT ((wide_t)1 << (WIDE_BITS-1)) #if ULLONG_MAX == (UINT_MAX * UINT_MAX + 2 * UINT_MAX) /* "unsigned" is half as wide as ullong */ @@ -44,48 +42,7 @@ typedef unsigned long half_t; #error Cant find an integer type which is half as wide as ullong #endif -/* Returns such x that x+1 > sqrt(N) */ -static inline half_t isqrt(wide_t N) -{ - half_t x; - - // Never called with N < 1 - //if (N == 0) - // return 0; - - x = HALF_MAX; - /* First approximation of x+1 > sqrt(N) - all-ones, half as many bits: - * 1xxxxx -> 111 (six bits to three) - * 01xxxx -> 111 - * 001xxx -> 011 - * 0001xx -> 011 and so on. - */ - // It is actually not performance-critical at all. - // Can simply start Newton loop with very conservative x=0xffffffff. - //wide_t mask_2bits; - //mask_2bits = TOPMOST_WIDE_BIT | (TOPMOST_WIDE_BIT >> 1); - //while (!(N & mask_2bits)) { - // x >>= 1; - // mask_2bits >>= 2; - //} - dbg("x:%"HALF_FMT"x", x); - - for (;;) { - half_t y = (x + N/x) / 2; - dbg("y:%x y^2:%llx", y, (wide_t)y * y); - /* - * "real" y may be one bit wider: 0x100000000 and get truncated to 0. - * In this case, "real" y is > x. The first check below is for this case: - */ - if (y == 0 || y >= x) { - dbg("isqrt(%llx)=%"HALF_FMT"x", N, x); - return x; - } - x = y; - } -} - -static NOINLINE half_t isqrt_odd(wide_t N) +static half_t isqrt_odd(wide_t N) { half_t s = isqrt(N); /* Subtract 1 from even s, odd s won't change: */ @@ -101,7 +58,7 @@ static NOINLINE void factorize(wide_t N) // unsigned count3; // unsigned count5; // unsigned count7; - // ^^^^^^^^^^^^^^^ commented-out simple siving code (easier to grasp). + // ^^^^^^^^^^^^^^^ commented-out simple sieving code (easier to grasp). // Faster sieving, using one word for potentially up to 6 counters: // count upwards in each mask, counter "triggers" when it sets its mask to "100[0]..." // 10987654321098765432109876543210 - bits 31-0 in 32-bit word @@ -116,7 +73,7 @@ static NOINLINE void factorize(wide_t N) MULTIPLE_OF_3 = 1 << 2, MULTIPLE_OF_5 = 1 << 6, MULTIPLE_OF_7 = 1 << 11, - MULTIPLE_3_5_7 = MULTIPLE_OF_3 | MULTIPLE_OF_5 | MULTIPLE_OF_7, + MULTIPLE_DETECTED = MULTIPLE_OF_3 | MULTIPLE_OF_5 | MULTIPLE_OF_7, }; unsigned sieve_word; @@ -137,15 +94,21 @@ static NOINLINE void factorize(wide_t N) * 18446744073709551601 = 53 348051774975651917 * the last factor requires testing up to * 589959129 - about 100 million iterations. + * The slowest case (largest prime) for N < 2^64 is + * factor 18446744073709551557 (0xffffffffffffffc5). */ max_factor = isqrt_odd(N); // count3 = 3; // count5 = 6; // count7 = 9; sieve_word = 0 + /* initial count for SHIFT_n is (n-1)/2*3: */ + (MULTIPLE_OF_3 - 3 * SHIFT_3) + (MULTIPLE_OF_5 - 6 * SHIFT_5) + (MULTIPLE_OF_7 - 9 * SHIFT_7) + //+ (MULTIPLE_OF_11 - 15 * SHIFT_11) + //+ (MULTIPLE_OF_13 - 18 * SHIFT_13) + //+ (MULTIPLE_OF_17 - 24 * SHIFT_17) ; factor = 3; for (;;) { @@ -174,7 +137,7 @@ static NOINLINE void factorize(wide_t N) // if (count3 && count5 && count7) // continue; sieve_word += INCREMENT_EACH; - if (!(sieve_word & MULTIPLE_3_5_7)) + if (!(sieve_word & MULTIPLE_DETECTED)) continue; /* * "factor" is multiple of 3 33% of the time (count3 reached 0), @@ -202,49 +165,54 @@ static NOINLINE void factorize(wide_t N) bb_putchar('\n'); } +static void factorize_numstr(const char *numstr) +{ + wide_t N; + + /* Leading + is ok (coreutils compat) */ + if (*numstr == '+') + numstr++; + N = bb_strtoull(numstr, NULL, 10); + if (errno) + bb_show_usage(); + printf("%llu:", N); + factorize(N); +} + int factor_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; int factor_main(int argc UNUSED_PARAM, char **argv) { -#if 0 /* test isqrt() correctness */ - wide_t n = argv[1] ? bb_strtoull(argv[1], NULL, 0) : time(NULL); - for (;;) { - half_t h; - if (--n == 0) - --n; - h = isqrt(n); - if (!(n & 0xff)) - printf("isqrt(%llx)=%"HALF_FMT"x\n", n, h); - if ((wide_t)h * h > n) - return 1; - h++; - if (h != 0 && (wide_t)h * h <= n) - return 1; - } -#endif - //// coreutils has undocumented option ---debug (three dashes) //getopt32(argv, ""); //argv += optind; argv++; - if (!*argv) - //TODO: read from stdin - bb_show_usage(); + if (!*argv) { + /* Read from stdin, several numbers per line are accepted */ + for (;;) { + char *numstr, *line; + line = xmalloc_fgetline(stdin); + if (!line) + return EXIT_SUCCESS; + numstr = line; + for (;;) { + char *end; + numstr = skip_whitespace(numstr); + if (!numstr[0]) + break; + end = skip_non_whitespace(numstr); + if (*end != '\0') + *end++ = '\0'; + factorize_numstr(numstr); + numstr = end; + } + free(line); + } + } do { - wide_t N; - const char *numstr; - - /* Coreutils compat */ - numstr = skip_whitespace(*argv); - if (*numstr == '+') - numstr++; - - N = bb_strtoull(numstr, NULL, 10); - if (errno) - bb_show_usage(); - printf("%llu:", N); - factorize(N); + /* Leading spaces are ok (coreutils compat) */ + factorize_numstr(skip_whitespace(*argv)); } while (*++argv); return EXIT_SUCCESS;