1 /*Written by Timothy B. Terriberry (tterribe@xiph.org) 1999-2009 public domain.
2 Based on the public domain ISAAC implementation by Robert J. Jenkins Jr.*/
6 #include <ccan/ilog/ilog.h>
10 #define ISAAC64_MASK ((uint64_t)0xFFFFFFFFFFFFFFFFULL)
12 /* Extract ISAAC64_SZ_LOG bits (starting at bit 3). */
13 static inline uint32_t lower_bits(uint64_t x)
15 return (x & ((ISAAC64_SZ-1) << 3)) >>3;
18 /* Extract next ISAAC64_SZ_LOG bits (starting at bit ISAAC64_SZ_LOG+2). */
19 static inline uint32_t upper_bits(uint32_t y)
21 return (y >> (ISAAC64_SZ_LOG+3)) & (ISAAC64_SZ-1);
24 static void isaac64_update(isaac64_ctx *_ctx){
35 b=_ctx->b+(++_ctx->c);
36 for(i=0;i<ISAAC64_SZ/2;i++){
38 a=~(a^a<<21)+m[i+ISAAC64_SZ/2];
39 m[i]=y=m[lower_bits(x)]+a+b;
40 r[i]=b=m[upper_bits(y)]+x;
42 a=(a^a>>5)+m[i+ISAAC64_SZ/2];
43 m[i]=y=m[lower_bits(x)]+a+b;
44 r[i]=b=m[upper_bits(y)]+x;
46 a=(a^a<<12)+m[i+ISAAC64_SZ/2];
47 m[i]=y=m[lower_bits(x)]+a+b;
48 r[i]=b=m[upper_bits(y)]+x;
50 a=(a^a>>33)+m[i+ISAAC64_SZ/2];
51 m[i]=y=m[lower_bits(x)]+a+b;
52 r[i]=b=m[upper_bits(y)]+x;
54 for(i=ISAAC64_SZ/2;i<ISAAC64_SZ;i++){
56 a=~(a^a<<21)+m[i-ISAAC64_SZ/2];
57 m[i]=y=m[lower_bits(x)]+a+b;
58 r[i]=b=m[upper_bits(y)]+x;
60 a=(a^a>>5)+m[i-ISAAC64_SZ/2];
61 m[i]=y=m[lower_bits(x)]+a+b;
62 r[i]=b=m[upper_bits(y)]+x;
64 a=(a^a<<12)+m[i-ISAAC64_SZ/2];
65 m[i]=y=m[lower_bits(x)]+a+b;
66 r[i]=b=m[upper_bits(y)]+x;
68 a=(a^a>>33)+m[i-ISAAC64_SZ/2];
69 m[i]=y=m[lower_bits(x)]+a+b;
70 r[i]=b=m[upper_bits(y)]+x;
77 static void isaac64_mix(uint64_t _x[8]){
78 static const unsigned char SHIFT[8]={9,9,23,15,14,20,17,14};
82 _x[(i+5)&7]^=_x[(i+7)&7]>>SHIFT[i];
86 _x[(i+5)&7]^=_x[(i+7)&7]<<SHIFT[i];
92 void isaac64_init(isaac64_ctx *_ctx,const unsigned char *_seed,int _nseed){
93 _ctx->a=_ctx->b=_ctx->c=0;
94 memset(_ctx->r,0,sizeof(_ctx->r));
95 isaac64_reseed(_ctx,_seed,_nseed);
98 void isaac64_reseed(isaac64_ctx *_ctx,const unsigned char *_seed,int _nseed){
106 if(_nseed>ISAAC64_SEED_SZ_MAX)_nseed=ISAAC64_SEED_SZ_MAX;
107 for(i=0;i<_nseed>>3;i++){
108 r[i]^=(uint64_t)_seed[i<<3|7]<<56|(uint64_t)_seed[i<<3|6]<<48|
109 (uint64_t)_seed[i<<3|5]<<40|(uint64_t)_seed[i<<3|4]<<32|
110 (uint64_t)_seed[i<<3|3]<<24|(uint64_t)_seed[i<<3|2]<<16|
111 (uint64_t)_seed[i<<3|1]<<8|_seed[i<<3];
117 for(j=1;j<_nseed;j++)ri|=(uint64_t)_seed[i<<3|j]<<(j<<3);
120 x[0]=x[1]=x[2]=x[3]=x[4]=x[5]=x[6]=x[7]=(uint64_t)0x9E3779B97F4A7C13ULL;
121 for(i=0;i<4;i++)isaac64_mix(x);
122 for(i=0;i<ISAAC64_SZ;i+=8){
123 for(j=0;j<8;j++)x[j]+=r[i+j];
125 memcpy(m+i,x,sizeof(x));
127 for(i=0;i<ISAAC64_SZ;i+=8){
128 for(j=0;j<8;j++)x[j]+=m[i+j];
130 memcpy(m+i,x,sizeof(x));
132 isaac64_update(_ctx);
135 uint64_t isaac64_next_uint64(isaac64_ctx *_ctx){
136 if(!_ctx->n)isaac64_update(_ctx);
137 return _ctx->r[--_ctx->n];
140 uint64_t isaac64_next_uint(isaac64_ctx *_ctx,uint64_t _n){
145 r=isaac64_next_uint64(_ctx);
149 while(((d+_n-1)&ISAAC64_MASK)<d);
153 /*Returns a uniform random float.
154 The expected value is within FLT_MIN (e.g., 1E-37) of 0.5.
155 _bits: An initial set of random bits.
156 _base: This should be -(the number of bits in _bits), up to -64.
157 Return: A float uniformly distributed between 0 (inclusive) and 1
159 The average value was measured over 2**32 samples to be
160 0.499991407275206357.*/
161 static float isaac64_float_bits(isaac64_ctx *_ctx,uint64_t _bits,int _base){
165 if(_base+FLT_MANT_DIG<FLT_MIN_EXP)return 0;
167 _bits=isaac64_next_uint64(_ctx);
169 nbits_needed=FLT_MANT_DIG-ilog64_nz(_bits);
171 ret=ldexpf((float)_bits,_base);
172 # if FLT_MANT_DIG>129
173 while(64-nbits_needed<0){
175 if(64-nbits_needed<0){
179 ret+=ldexpf((float)isaac64_next_uint64(_ctx),_base);
181 _bits=isaac64_next_uint64(_ctx)>>(64-nbits_needed);
182 ret+=ldexpf((float)_bits,_base-nbits_needed);
185 _bits=_bits<<nbits_needed|isaac64_next_uint64(_ctx)>>(64-nbits_needed);
188 else _bits>>=-nbits_needed;
190 ret=ldexpf((float)_bits,_base-nbits_needed);
195 float isaac64_next_float(isaac64_ctx *_ctx){
196 return isaac64_float_bits(_ctx,0,0);
199 float isaac64_next_signed_float(isaac64_ctx *_ctx){
201 bits=isaac64_next_uint64(_ctx);
202 return (1|-((int)bits&1))*isaac64_float_bits(_ctx,bits>>1,-63);
205 /*Returns a uniform random double.
206 _bits: An initial set of random bits.
207 _base: This should be -(the number of bits in _bits), up to -64.
208 Return: A double uniformly distributed between 0 (inclusive) and 1
210 The average value was measured over 2**32 samples to be
211 0.499990992392019273.*/
212 static double isaac64_double_bits(isaac64_ctx *_ctx,uint64_t _bits,int _base){
216 if(_base+DBL_MANT_DIG<DBL_MIN_EXP)return 0;
218 _bits=isaac64_next_uint64(_ctx);
220 nbits_needed=DBL_MANT_DIG-ilog64_nz(_bits);
222 ret=ldexp((double)_bits,_base);
223 # if DBL_MANT_DIG>129
224 while(64-nbits_needed<0){
226 if(64-nbits_needed<0){
230 ret+=ldexp((double)isaac64_next_uint64(_ctx),_base);
232 _bits=isaac64_next_uint64(_ctx)>>(64-nbits_needed);
233 ret+=ldexp((double)_bits,_base-nbits_needed);
236 _bits=_bits<<nbits_needed|isaac64_next_uint64(_ctx)>>(64-nbits_needed);
239 else _bits>>=-nbits_needed;
241 ret=ldexp((double)_bits,_base-nbits_needed);
246 double isaac64_next_double(isaac64_ctx *_ctx){
247 return isaac64_double_bits(_ctx,0,0);
250 double isaac64_next_signed_double(isaac64_ctx *_ctx){
252 bits=isaac64_next_uint64(_ctx);
253 return (1|-((int)bits&1))*isaac64_double_bits(_ctx,bits>>1,-63);