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/* -*- linux-c -*- */
/* Math functions
* Copyright (C) 2005-2012 Red Hat Inc.
*
* This file is part of systemtap, and is free software. You can
* redistribute it and/or modify it under the terms of the GNU General
* Public License (GPL); either version 2, or (at your option) any
* later version.
*/
#ifndef _STAPDYN_ARITH_C_
#define _STAPDYN_ARITH_C_
/** @file arith.
* @brief Implements various arithmetic-related helper functions
*/
/** Divide x by y. In case of division-by-zero,
* set context error string, and return 0
*/
static int64_t _stp_div64 (const char **error, int64_t x, int64_t y)
{
// check for division-by-zero
if (unlikely (y == 0)) {
if (error) *error = "division by 0";
return 0;
}
if (unlikely (y == -1))
return -x;
return x/y;
}
/** Modulo x by y. In case of division-by-zero,
* set context error string, and return any 0
*/
static int64_t _stp_mod64 (const char **error, int64_t x, int64_t y)
{
// check for division-by-zero
if (unlikely (y == 0)) {
if (error) *error = "division by 0";
return 0;
}
if (unlikely (y == 1 || y == -1))
return 0;
return x%y;
}
static unsigned long _stp_random_u_init(void)
{
unsigned long seed;
ssize_t count = 0;
int fd = open("/dev/urandom", O_RDONLY);
if (fd >= 0) {
count = read(fd, &seed, sizeof(seed));
close(fd);
}
/* If urandom fails for any reason, this is a crude fallback */
if (count != sizeof(seed)) {
struct timespec ts;
(void)clock_gettime(CLOCK_MONOTONIC_RAW, &ts);
seed = ts.tv_sec * NSEC_PER_SEC + ts.tv_nsec;
}
return seed;
}
/** Return a random integer between 0 and n - 1.
* @param n how far from zero to go. Make it positive but less than a million or so.
*/
static unsigned long _stp_random_u (unsigned long n)
{
static unsigned long seed;
static int initialized_p = 0;
if (unlikely (! initialized_p)) {
seed = _stp_random_u_init();
initialized_p = 1;
}
/* from glibc rand man page */
seed = seed * 1103515245 + 12345;
return (n == 0 ? 0 : seed % n);
}
/** Return a random integer between -n and n.
* @param n how far from zero to go. Make it positive but less than a million or so.
*/
static int _stp_random_pm (unsigned n)
{
return -(int)n + (int)_stp_random_u (2*n + 1);
}
#endif /* _STAPDYN_ARITH_C_ */
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