1 /*
2 ------------------------------------------------------------------------------
3 isaac.c: By Bob Jenkins. My random number generator, ISAAC.
4 MODIFIED:
5 960327: Creation (addition of randinit, really)
6 970719: use context, not global variables, for internal state
7 980324: make a portable version
8 991209: modified for inclusion with GNU Backgammon by Gary Wong
9 070121: modified for inclusion with flam3 by Erik Reckase
10 ------------------------------------------------------------------------------
11 */
12
13 #include "isaacs.h"
14 #include "isaac.h"
15
16 #define ind(mm,x) ((mm)[(x>>2)&(RANDSIZ-1)])
17 #define rngstep(mix,a,b,mm,m,m2,r,x) \
18 { \
19 x = *m; \
20 a = ((a^(mix)) + *(m2++)) & 0xffffffff; \
21 *(m++) = y = (ind(mm,x) + a + b) & 0xffffffff; \
22 *(r++) = b = (ind(mm,y>>RANDSIZL) + x) & 0xffffffff; \
23 }
24
isaac(randctx * ctx)25 void isaac(randctx *ctx)
26 {
27 register ub4 a,b,x,y,*m,*mm,*m2,*r,*mend;
28 mm=ctx->randmem; r=ctx->randrsl;
29 a = ctx->randa; b = (ctx->randb + (++ctx->randc)) & 0xffffffff;
30 for (m = mm, mend = m2 = m+(RANDSIZ/2); m<mend; )
31 {
32 rngstep( a<<13, a, b, mm, m, m2, r, x);
33 rngstep( a>>6 , a, b, mm, m, m2, r, x);
34 rngstep( a<<2 , a, b, mm, m, m2, r, x);
35 rngstep( a>>16, a, b, mm, m, m2, r, x);
36 }
37 for (m2 = mm; m2<mend; )
38 {
39 rngstep( a<<13, a, b, mm, m, m2, r, x);
40 rngstep( a>>6 , a, b, mm, m, m2, r, x);
41 rngstep( a<<2 , a, b, mm, m, m2, r, x);
42 rngstep( a>>16, a, b, mm, m, m2, r, x);
43 }
44 ctx->randb = b; ctx->randa = a;
45 }
46
47
48 #define mix(a,b,c,d,e,f,g,h) \
49 { \
50 a^=b<<11; d+=a; b+=c; \
51 b^=c>>2; e+=b; c+=d; \
52 c^=d<<8; f+=c; d+=e; \
53 d^=e>>16; g+=d; e+=f; \
54 e^=f<<10; h+=e; f+=g; \
55 f^=g>>4; a+=f; g+=h; \
56 g^=h<<8; b+=g; h+=a; \
57 h^=a>>9; c+=h; a+=b; \
58 }
59
60 /* if (flag==TRUE), then use the contents of randrsl[] to initialize mm[]. */
irandinit(randctx * ctx,word flag)61 void irandinit(randctx *ctx, word flag)
62 {
63 word i;
64 ub4 a,b,c,d,e,f,g,h;
65 ub4 *m,*r;
66 ctx->randa = ctx->randb = ctx->randc = 0;
67 m=ctx->randmem;
68 r=ctx->randrsl;
69 a=b=c=d=e=f=g=h=0x9e3779b9; /* the golden ratio */
70
71 for (i=0; i<4; ++i) /* scramble it */
72 {
73 mix(a,b,c,d,e,f,g,h);
74 }
75
76 if (flag)
77 {
78 /* initialize using the contents of r[] as the seed */
79 for (i=0; i<RANDSIZ; i+=8)
80 {
81 a+=r[i ]; b+=r[i+1]; c+=r[i+2]; d+=r[i+3];
82 e+=r[i+4]; f+=r[i+5]; g+=r[i+6]; h+=r[i+7];
83 mix(a,b,c,d,e,f,g,h);
84 m[i ]=a; m[i+1]=b; m[i+2]=c; m[i+3]=d;
85 m[i+4]=e; m[i+5]=f; m[i+6]=g; m[i+7]=h;
86 }
87 /* do a second pass to make all of the seed affect all of m */
88 for (i=0; i<RANDSIZ; i+=8)
89 {
90 a+=m[i ]; b+=m[i+1]; c+=m[i+2]; d+=m[i+3];
91 e+=m[i+4]; f+=m[i+5]; g+=m[i+6]; h+=m[i+7];
92 mix(a,b,c,d,e,f,g,h);
93 m[i ]=a; m[i+1]=b; m[i+2]=c; m[i+3]=d;
94 m[i+4]=e; m[i+5]=f; m[i+6]=g; m[i+7]=h;
95 }
96 }
97 else
98 {
99 for (i=0; i<RANDSIZ; i+=8)
100 {
101 /* fill in mm[] with messy stuff */
102 mix(a,b,c,d,e,f,g,h);
103 m[i ]=a; m[i+1]=b; m[i+2]=c; m[i+3]=d;
104 m[i+4]=e; m[i+5]=f; m[i+6]=g; m[i+7]=h;
105 }
106 }
107
108 isaac(ctx); /* fill in the first set of results */
109 ctx->randcnt=RANDSIZ; /* prepare to use the first set of results */
110 }
111