runtime/dyninst/arith.c - systemtap

Functions defined

Macros defined

Source code

/* -*- 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_ */