/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*      Copyright (c) 1988 AT&T */
/*        All Rights Reserved   */

/*
 *      drand48, etc. pseudo-random number generator
 *      This implementation assumes unsigned short integers of at least
 *      16 bits, long integers of at least 32 bits, and ignores
 *      overflows on adding or multiplying two unsigned integers.
 *      Two's-complement representation is assumed in a few places.
 *      Some extra masking is done if unsigneds are exactly 16 bits
 *      or longs are exactly 32 bits, but so what?
 *      An assembly-language implementation would run significantly faster.
 */
/*
 *      New assumptions (supercede those stated above) for 64-bit work.
 *      Longs are now 64 bits, and we are bound by standards to return
 *      type long, hovever all internal calculations where long was
 *      previously used (32 bit precision) are now using the int32_t
 *      type (32 bit precision in both ILP32 and LP64 worlds).
 */

#include <sys/mutex.h>

static kmutex_t seed_lock;
static int      init48done = 0;

#define EXPORT0(TYPE, fn, fnu)  TYPE fn() { \
        TYPE res; \
        mutex_enter(&seed_lock); \
        res = fnu(); \
        mutex_exit(&seed_lock); \
        return (res); }
#define EXPORT1(TYPE, fn, fnu)  TYPE fn(unsigned short xsubi[3]) { \
        TYPE res; \
        mutex_enter(&seed_lock); \
        res = fnu(xsubi); \
        mutex_exit(&seed_lock); \
        return (res); }

#define N       16
#define MASK    ((unsigned)(1 << (N - 1)) + (1 << (N - 1)) - 1)
#define LOW(x)  ((unsigned)(x) & MASK)
#define HIGH(x) LOW((x) >> N)
#define MUL(x, y, z)    { int32_t l = (int32_t)(x) * (int32_t)(y); \
                (z)[0] = LOW(l); (z)[1] = HIGH(l); }
#define CARRY(x, y)     ((int32_t)(x) + (int32_t)(y) > MASK)
#define ADDEQU(x, y, z) (z = CARRY(x, (y)), x = LOW(x + (y)))
#define X0      0x330E
#define X1      0xABCD
#define X2      0x1234
#define A0      0xE66D
#define A1      0xDEEC
#define A2      0x5
#define C       0xB
#define SET3(x, x0, x1, x2)     ((x)[0] = (x0), (x)[1] = (x1), (x)[2] = (x2))
#define SETLOW(x, y, n) SET3(x, LOW((y)[n]), LOW((y)[(n)+1]), LOW((y)[(n)+2]))
#define SEED(x0, x1, x2) (SET3(x, x0, x1, x2), SET3(a, A0, A1, A2), c = C)
#define REST(v) for (i = 0; i < 3; i++) { xsubi[i] = x[i]; x[i] = temp[i]; } \
                return (v)
#define NEST(TYPE, f, F) static TYPE f(unsigned short *xsubi) { \
        int i; TYPE v; unsigned temp[3]; \
        for (i = 0; i < 3; i++) { temp[i] = x[i]; x[i] = LOW(xsubi[i]); }  \
        v = F(); REST(v); }

/* Way ugly solution to problem names, but it works */
#define x       _drand48_x
#define a       _drand48_a
#define c       _drand48_c
/* End way ugly */
static unsigned x[3] = { X0, X1, X2 }, a[3] = { A0, A1, A2 }, c = C;
static unsigned short lastx[3];
static void next(void);

static long
ipf_r_lrand48_u(void)
{
        next();
        return ((long)((int32_t)x[2] << (N - 1)) + (x[1] >> 1));
}

static void
init48(void)
{
        mutex_init(&seed_lock, 0L, MUTEX_DRIVER, 0L);
        init48done = 1;
}

static long
ipf_r_mrand48_u(void)
{
        next();
        return ((long)((int32_t)x[2] << N) + x[1]);
}

static void
next(void)
{
        unsigned p[2], q[2], r[2], carry0, carry1;

        MUL(a[0], x[0], p);
        ADDEQU(p[0], c, carry0);
        ADDEQU(p[1], carry0, carry1);
        MUL(a[0], x[1], q);
        ADDEQU(p[1], q[0], carry0);
        MUL(a[1], x[0], r);
        x[2] = LOW(carry0 + carry1 + CARRY(p[1], r[0]) + q[1] + r[1] +
                a[0] * x[2] + a[1] * x[1] + a[2] * x[0]);
        x[1] = LOW(p[1] + r[0]);
        x[0] = LOW(p[0]);
}

void
ipf_r_srand48(long seedval)
{
        int32_t fixseed = (int32_t)seedval;     /* limit to 32 bits */

        if (init48done == 0)
                init48();
        mutex_enter(&seed_lock);
        SEED(X0, LOW(fixseed), HIGH(fixseed));
        mutex_exit(&seed_lock);
}

EXPORT0(long, ipf_r_lrand48, ipf_r_lrand48_u)

#include <sys/random.h>

unsigned
ipf_random()
{
        static int seeded = 0;

        if (seeded == 0) {
                long seed;

                /*
                 * Keep reseeding until some good randomness comes from the
                 * kernel. One of two things will happen: it will succeed or
                 * it will fail (with poor randomness), thus creating NAT
                 * sessions will be "slow" until enough randomness is gained
                 * to not need to get more. It isn't necessary to initialise
                 * seed as it will just pickup whatever random garbage has
                 * been left on the heap and that's good enough until we
                 * get some good garbage.
                 */
                if (random_get_bytes((uint8_t *)&seed, sizeof (seed)) == 0)
                        seeded = 1;
                ipf_r_srand48(seed);
        }

        return (unsigned)ipf_r_lrand48();
}