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authorDenys Vlasenko <vda.linux@googlemail.com>2017-04-11 05:34:56 (GMT)
committerDenys Vlasenko <vda.linux@googlemail.com>2017-04-11 05:34:56 (GMT)
commit8a134ec68075fc2fd415558bcf6a37cda3ff285f (patch)
treee6c4927ebcb071b6dcb6e9832ebe6d7f4b721461
parent10673c44f11045a0c99b19f32930097e9b3ae148 (diff)
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libbb: move isqrt from factor, use it in diff too
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
-rw-r--r--coreutils/factor.c19
-rw-r--r--editors/diff.c11
-rw-r--r--include/libbb.h2
-rw-r--r--libbb/isqrt.c60
4 files changed, 63 insertions, 29 deletions
diff --git a/coreutils/factor.c b/coreutils/factor.c
index f910fdb..11cc04f 100644
--- 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 0eb825c..3304edb 100644
--- 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 a2c699b..0407163 100644
--- 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
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