/* -*- mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*- */
// vim: ft=cpp:expandtab:ts=8:sw=4:softtabstop=4:
#ident "$Id$"
#ident "Copyright (c) 2007-2013 Tokutek Inc.  All rights reserved."

#ifndef TOKU_RANDOM_H
#define TOKU_RANDOM_H

#include <config.h>
#include <toku_portability.h>
#include <toku_assert.h>
#include <stdlib.h>
#include <stdint.h>
#include <limits.h>

#if defined(HAVE_RANDOM_R)
// Definition of randu62 and randu64 assume myrandom_r generates 31 low-order bits
static_assert(RAND_MAX == INT32_MAX, "Unexpected RAND_MAX");
static inline int
myinitstate_r(unsigned int seed, char *statebuf, size_t statelen, struct random_data *buf)
{
    return initstate_r(seed, statebuf, statelen, buf);
}
static inline int32_t
myrandom_r(struct random_data *buf)
{
    int32_t x;
    int r = random_r(buf, &x);
    lazy_assert_zero(r);
    return x;
}
#elif defined(HAVE_NRAND48)
struct random_data {
    unsigned short xsubi[3];
};
static inline int
myinitstate_r(unsigned int seed, char *UU(statebuf), size_t UU(statelen), struct random_data *buf)
{
    buf->xsubi[0] = (seed & 0xffff0000) >> 16;
    buf->xsubi[0] = (seed & 0x0000ffff);
    buf->xsubi[2] = (seed & 0x00ffff00) >> 8;
    return 0;
}
static inline int32_t
myrandom_r(struct random_data *buf)
{
    int32_t x = nrand48(buf->xsubi);
    return x;
}
#else
# error "no suitable reentrant random function available (checked random_r and nrand48)"
#endif

static inline uint64_t
randu62(struct random_data *buf)
{
    uint64_t a = myrandom_r(buf);
    uint64_t b = myrandom_r(buf);
    return (a | (b << 31));
}

static inline uint64_t
randu64(struct random_data *buf)
{
    uint64_t r62 = randu62(buf);
    uint64_t c = myrandom_r(buf);
    return (r62 | ((c & 0x3) << 62));
}

static inline uint32_t
rand_choices(struct random_data *buf, uint32_t choices) {
    invariant(choices >= 2);
    invariant(choices < INT32_MAX);
    uint32_t bits = 2;
    while (bits < choices) {
        bits *= 2;
    }
    --bits;

    uint32_t result;
    do {
        result = myrandom_r(buf) & bits;
    } while (result >= choices);

    return result;
}

#endif // TOKU_RANDOM_H