libbb: move isqrt from factor, use it in diff too

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/coreutils/factor.c b/coreutils/factor.c
index f910fdb4494fbf529257201ed9c3ad70bbaf537e..11cc04f926aa70db5002960b94b96e0bac2092f0 100644 (file)
--- a/coreutils/factor.c
+++ b/coreutils/factor.c
@@ -44,24 +44,7 @@ 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;
-       unsigned shift;
-
-       shift = WIDE_BITS - 2;
-       x = 0;
-       do {
-               x = (x << 1) + 1;
-               if ((wide_t)x * x > (N >> shift))
-                       x--; /* whoops, that +1 was too much */
-               shift -= 2;
-       } while ((int)shift >= 0);
-       return x;
-}
-
-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: */

diff --git a/editors/diff.c b/editors/diff.c
index 0eb825cfb144bd193c17975bebd58696287e7e89..3304edb26f9a4c7703ceb1e3a262526b5c685de9 100644 (file)
--- a/editors/diff.c
+++ b/editors/diff.c
@@ -295,17 +295,6 @@ static int search(const int *c, int k, int y, const struct cand *list)
        }
 }
 
-static unsigned isqrt(unsigned n)
-{
-       unsigned x = 1;
-       while (1) {
-               const unsigned y = x;
-               x = ((n / x) + x) >> 1;
-               if (x <= (y + 1) && x >= (y - 1))
-                       return x;
-       }
-}
-
 static void stone(const int *a, int n, const int *b, int *J, int pref)
 {
        const unsigned isq = isqrt(n);

diff --git a/include/libbb.h b/include/libbb.h
index a2c699b54e326f7eab9c289218c6794ae3890bcd..04071639af85a71725f7447bc56b79eeaf0332b4 100644 (file)
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -342,6 +342,8 @@ extern int *const bb_errno;
 uint64_t bb_bswap_64(uint64_t x) FAST_FUNC;
 #endif
 
+unsigned long FAST_FUNC isqrt(unsigned long long N);
+
 unsigned long long monotonic_ns(void) FAST_FUNC;
 unsigned long long monotonic_us(void) FAST_FUNC;
 unsigned long long monotonic_ms(void) FAST_FUNC;

diff --git a/libbb/isqrt.c b/libbb/isqrt.c
new file mode 100644 (file)
index 0000000..817b7d0
--- /dev/null
+++ b/libbb/isqrt.c
@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2017 Denys Vlasenko <vda.linux@googlemail.com>
+ *
+ * Licensed under GPLv2, see file LICENSE in this source tree.
+ */
+
+//kbuild:lib-y += isqrt.o
+
+#ifndef ISQRT_TEST
+# include "libbb.h"
+#else
+/* gcc -DISQRT_TEST -Wall -O2 isqrt.c -oisqrt && ./isqrt $((RANDOM*RANDOM)) */
+# include <stdlib.h>
+# include <stdio.h>
+# include <time.h>
+# define FAST_FUNC /* nothing */
+#endif
+
+/* Returns such x that x+1 > sqrt(N) */
+unsigned long FAST_FUNC isqrt(unsigned long long N)
+{
+       unsigned long x;
+       unsigned shift;
+#define LL_WIDTH_BITS (unsigned)(sizeof(N)*8)
+
+       shift = LL_WIDTH_BITS - 2;
+       x = 0;
+       do {
+               x = (x << 1) + 1;
+               if ((unsigned long long)x * x > (N >> shift))
+                       x--; /* whoops, that +1 was too much */
+               shift -= 2;
+       } while ((int)shift >= 0);
+       return x;
+}
+
+#ifdef ISQRT_TEST
+int main(int argc, char **argv)
+{
+       unsigned long long n = argv[1] ? strtoull(argv[1], NULL, 0) : time(NULL);
+       for (;;) {
+               unsigned long h;
+               n--;
+               h = isqrt(n);
+               if (!(n & 0xffff))
+                       printf("isqrt(%llx)=%lx\n", n, h);
+               if ((unsigned long long)h * h > n) {
+                       printf("BAD1: isqrt(%llx)=%lx\n", n, h);
+                       return 1;
+               }
+               h++;
+               if ((unsigned long long)h * h != 0 /* this can overflow to 0 - not a bug */
+                && (unsigned long long)h * h <= n)
+               {
+                       printf("BAD2: isqrt(%llx)=%lx\n", n, h);
+                       return 1;
+               }
+       }
+}
+#endif