/** Bob Jenkin's random number generator

 *

 * Bob's random number generator, ISAAC.  Public Domain.

 *

 *  http://burtleburtle.net/bob/rand/isaac.html

 *

 * @file src/lib/util/isaac.c

 *

 * @author Bob Jenkins.

 */

RCSID("$Id: 26a821633e00d0fed1f4db9f17345c271f85a515 $")

#include <freeradius-devel/util/rand.h>

#define RANDSIZL   (8)  /* I recommend 8 for crypto, 4 for simulations */

#define RANDSIZ    (1 << RANDSIZL)

#define ind(mm,x)  ((mm)[(x >> 2) &(RANDSIZ-1)])

#define rngstep(mix, a, b, mm, m, m2, r, x) \

do { \

  x = *m;  \

  a = ((a^(mix)) + *(m2++)) & 0xffffffff; \

  *(m++) = y = (ind(mm, x) + a + b) & 0xffffffff; \

  *(r++) = b = (ind(mm, y >> RANDSIZL) + x) & 0xffffffff; \

} while (0)

#ifdef ISAAC_PLUS

/*

 *  https://eprint.iacr.org/2006/438.pdf

 *

 *  - replace shift by rotate

 *  - replace "a+b" with "a^b"

 *  - change "x+s" to "x+(s^a)"

 */

#define rotr(x, n) (((x) << n) | ((x) >> (32 - n)))

#define ind(mm,x)  ((mm)[rotr(x, 2) & (RANDSIZ-1)])

#define rngstep(mix, a, b, mm, m, m2, r, x) \

do { \

  x = *m;  \

  a = ((a^(mix)) + *(m2++)) & 0xffffffff; \

  *(m++) = y = (ind(mm, x) + (a ^ b)) & 0xffffffff; \

  *(r++) = b = ((ind(mm, y >> RANDSIZL) ^ a) + x) & 0xffffffff; \

} while (0)

#endif

void fr_isaac(fr_randctx *ctx)

{

  register uint32_t a, b, x, y, *m, *mm, *m2, *r, *mend;

  mm = ctx->randmem;

  r = ctx->randrsl;

  a = ctx->randa;

  b = (ctx->randb + (++ctx->randc)) & 0xffffffff;

  for (m = mm, mend = m2 = m + (RANDSIZ / 2); m < mend; ) {

    rngstep(a << 13, a, b, mm, m, m2, r, x);

    rngstep(a >> 6 , a, b, mm, m, m2, r, x);

    rngstep(a << 2 , a, b, mm, m, m2, r, x);

    rngstep(a >> 16, a, b, mm, m, m2, r, x);

  }

  for (m2 = mm; m2 < mend; ) {

    rngstep(a << 13, a, b, mm, m, m2, r, x);

    rngstep(a >> 6 , a, b, mm, m, m2, r, x);

    rngstep(a << 2 , a, b, mm, m, m2, r, x);

    rngstep(a >> 16, a, b, mm, m, m2, r, x);

  }

  ctx->randb = b;

  ctx->randa = a;

}

#define mix(a,b,c,d,e,f,g,h) \

do { \

  a ^= b << 11; d += a; b += c; \

  b ^= c >> 2;  e += b; c += d; \

  c ^= d << 8;  f += c; d += e; \

  d ^= e >> 16; g += d; e += f; \

  e ^= f << 10; h += e; f += g; \

  f ^= g >> 4;  a += f; g += h; \

  g ^= h << 8;  b += g; h += a; \

  h ^= a >> 9;  c += h; a += b; \

} while (0)

/* if (flag==1), then use the contents of randrsl[] to initialize mm[]. */

void fr_isaac_init(fr_randctx *ctx, int flag)

{

  int   i;

  uint32_t  a, b, c, d, e, f, g, h;

  uint32_t  *m, *r;

  ctx->randa = ctx->randb = ctx->randc = 0;

  m = ctx->randmem;

  r = ctx->randrsl;

  a = b = c = d = e = f = g = h = 0x9e3779b9;  /* the golden ratio */

  /* scramble it */

  for (i = 0; i < 4; ++i) {

    /* coverity[overflow_const] */

    mix(a, b, c, d, e, f, g, h);

  }

  if (flag) {

    /* initialize using the contents of r[] as the seed */

    for (i = 0; i < RANDSIZ; i += 8) {

      a += r[i    ]; b += r[i + 1]; c +=r [i + 2]; d += r[i + 3];

      e += r[i + 4]; f += r[i + 5]; g +=r [i + 6]; h += r[i + 7];

      mix(a, b, c, d, e, f, g, h);

      m[i    ] = a; m[i + 1] = b; m[i + 2] = c; m[i + 3] = d;

      m[i + 4] = e; m[i + 5] = f; m[i + 6] = g; m[i + 7] = h;

    }

    /* do a second pass to make all of the seed affect all of m */

    for (i = 0; i < RANDSIZ; i += 8) {

      a += m[i    ]; b += m[i + 1]; c += m[i + 2]; d += m[i + 3];

      e += m[i + 4]; f += m[i + 5]; g += m[i + 6]; h += m[i + 7];

      mix(a, b, c, d, e, f, g, h);

      m[i    ] = a; m[i + 1] = b; m[i + 2] = c; m[i + 3] = d;

      m[i + 4] = e; m[i + 5] = f; m[i + 6] = g; m[i + 7] = h;

    }

  } else {

    for (i = 0; i < RANDSIZ; i += 8) {

      /* fill in mm[] with messy stuff */

      mix(a, b, c, d, e, f, g, h);

      m[i    ] = a; m[i + 1] = b; m[i + 2] = c; m[i + 3] = d;

      m[i + 4] = e; m[i + 5] = f; m[i + 6] = g; m[i + 7] = h;

    }

  }

  fr_isaac(ctx);       /* fill in the first set of results */

  ctx->randcnt = RANDSIZ;  /* prepare to use the first set of results */

}

#ifdef TEST

/*

 *  For testing.  Output should be the same as

 *

 *  http://burtleburtle.net/bob/rand/randvect.txt

 */

int main()

{

  uint32_t  i,j;

  fr_randctx  ctx;

  ctx.randa = ctx.randb = ctx.randc = (uint32_t)0;

  for (i = 0; i < 256; ++i) ctx.randrsl[i] = (uint32_t)0;

  fr_isaac_init(&ctx, 1);

  for (i = 0; i < 2; ++i) {

    fr_isaac(&ctx);

    for (j = 0; j < 256; ++j) {

      printf("%.8lx",ctx.randrsl[j]);

      if ((j & 7) == 7) printf("\n");

    }

  }

}

#endif