/*
------------------------------------------------------------------------------
rand.c: By Bob Jenkins.  My random number generator, ISAAC.  Public Domain.
MODIFIED:
  960327: Creation (addition of randinit, really)
  970719: use context, not global variables, for internal state
  980324: added main (ifdef'ed out), also rearranged randinit()
  010626: Note that this is public domain
------------------------------------------------------------------------------
*/
#include <stdint.h>
#include "rand.h"

#define ind(mm,x)  (*(uint32_t *)((uint8_t *)(mm) + ((x) & ((RANDSIZ-1)<<2))))
#define rngstep(mix,a,b,mm,m,m2,r,x) \
{ \
  x = *m;  \
  a = (a^(mix)) + *(m2++); \
  *(m++) = y = ind(mm,x) + a + b; \
  *(r++) = b = ind(mm,y>>RANDSIZL) + x; \
}

void isaac(struct 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);
    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) \
{ \
   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; \
}

/* if (flag==TRUE), then use the contents of randrsl[] to initialize mm[]. */
void randinit(struct randctx *ctx, uint_fast8_t flag)
{
    uint_fast32_t 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 */

    for (i = 0; i < 4; ++i) {	/* scramble it */
	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 {
	/* fill in m[] with messy stuff */
	for (i = 0; i < RANDSIZ; i += 8) {
	    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;
	}
    }

    isaac(ctx);			/* fill in the first set of results */
    ctx->randcnt = RANDSIZ;	/* prepare to use the first set of results */
}


#ifdef NEVER

#include <stdio.h>

int main()
{
    uint32_t i, j;
    struct randctx ctx;
    ctx.randa = ctx.randb = ctx.randc = (uint32_t) 0;
    for (i = 0; i < 256; ++i)
	ctx.randrsl[i] = (uint32_t) 0;
    randinit(&ctx, 1);
    for (i = 0; i < 2; ++i) {
	isaac(&ctx);
	for (j = 0; j < 256; ++j) {
	    printf("%.8x", ctx.randrsl[j]);
	    if ((j & 7) == 7)
		printf("\n");
	}
    }
}
#endif