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

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Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2017-04-11 07:34:56 +02:00
parent 10673c44f1
commit 8a134ec680
4 changed files with 63 additions and 29 deletions
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19
coreutils/factor.c
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@ -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: */

11
editors/diff.c
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@ -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);

2
include/libbb.h
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@ -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;

60
libbb/isqrt.c Normal file
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@ -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