/*
------------------------------------------------------------------------------
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
------------------------------------------------------------------------------
*/
#ifndef STANDARD
#include "standard.h"
#endif
#ifndef RAND
#include "rand.h"
#endif


#define ind(mm, x) (*(ub4 *)((ub1 *)(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(ctx) randctx *ctx;
{
	register ub4 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(ctx, flag) randctx *ctx;
word flag;
{
	word i;
	ub4 a, b, c, d, e, f, g, h;
	ub4 *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
int main()
{
	ub4 i, j;
	randctx ctx;
	ctx.randa = ctx.randb = ctx.randc = (ub4)0;
	for(i = 0; i < 256; ++i)
		ctx.randrsl[i] = (ub4)0;
	randinit(&ctx, TRUE);
	for(i = 0; i < 2; ++i) {
		isaac(&ctx);
		for(j = 0; j < 256; ++j) {
			printf("%.8lx", ctx.randrsl[j]);
			if((j & 7) == 7)
				printf("\n");
		}
	}
}
#endif
