140 lines
3.8 KiB
C
140 lines
3.8 KiB
C
/*Written by Timothy B. Terriberry (tterribe@xiph.org) 1999-2009 public domain.
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Based on the public domain implementation by Robert J. Jenkins Jr.*/
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#include <float.h>
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#include <math.h>
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#include <string.h>
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#include "isaac.h"
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#define ISAAC_MASK (0xFFFFFFFFU)
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static void isaac_update(isaac_ctx *_ctx){
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unsigned *m;
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unsigned *r;
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unsigned a;
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unsigned b;
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unsigned x;
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unsigned y;
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int i;
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m=_ctx->m;
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r=_ctx->r;
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a=_ctx->a;
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b=(_ctx->b+(++_ctx->c))&ISAAC_MASK;
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for(i=0;i<ISAAC_SZ/2;i++){
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x=m[i];
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a=((a^a<<13)+m[i+ISAAC_SZ/2])&ISAAC_MASK;
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m[i]=y=(m[(x&(ISAAC_SZ-1)<<2)>>2]+a+b)&ISAAC_MASK;
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r[i]=b=(m[y>>(ISAAC_SZ_LOG+2)&(ISAAC_SZ-1)]+x)&ISAAC_MASK;
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x=m[++i];
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a=((a^a>>6)+m[i+ISAAC_SZ/2])&ISAAC_MASK;
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m[i]=y=(m[(x&(ISAAC_SZ-1)<<2)>>2]+a+b)&ISAAC_MASK;
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r[i]=b=(m[y>>(ISAAC_SZ_LOG+2)&(ISAAC_SZ-1)]+x)&ISAAC_MASK;
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x=m[++i];
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a=((a^a<<2)+m[i+ISAAC_SZ/2])&ISAAC_MASK;
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m[i]=y=(m[(x&(ISAAC_SZ-1)<<2)>>2]+a+b)&ISAAC_MASK;
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r[i]=b=(m[y>>(ISAAC_SZ_LOG+2)&(ISAAC_SZ-1)]+x)&ISAAC_MASK;
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x=m[++i];
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a=((a^a>>16)+m[i+ISAAC_SZ/2])&ISAAC_MASK;
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m[i]=y=(m[(x&(ISAAC_SZ-1)<<2)>>2]+a+b)&ISAAC_MASK;
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r[i]=b=(m[y>>(ISAAC_SZ_LOG+2)&(ISAAC_SZ-1)]+x)&ISAAC_MASK;
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}
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for(i=ISAAC_SZ/2;i<ISAAC_SZ;i++){
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x=m[i];
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a=((a^a<<13)+m[i-ISAAC_SZ/2])&ISAAC_MASK;
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m[i]=y=(m[(x&(ISAAC_SZ-1)<<2)>>2]+a+b)&ISAAC_MASK;
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r[i]=b=(m[y>>(ISAAC_SZ_LOG+2)&(ISAAC_SZ-1)]+x)&ISAAC_MASK;
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x=m[++i];
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a=((a^a>>6)+m[i-ISAAC_SZ/2])&ISAAC_MASK;
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m[i]=y=(m[(x&(ISAAC_SZ-1)<<2)>>2]+a+b)&ISAAC_MASK;
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r[i]=b=(m[y>>(ISAAC_SZ_LOG+2)&(ISAAC_SZ-1)]+x)&ISAAC_MASK;
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x=m[++i];
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a=((a^a<<2)+m[i-ISAAC_SZ/2])&ISAAC_MASK;
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m[i]=y=(m[(x&(ISAAC_SZ-1)<<2)>>2]+a+b)&ISAAC_MASK;
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r[i]=b=(m[y>>(ISAAC_SZ_LOG+2)&(ISAAC_SZ-1)]+x)&ISAAC_MASK;
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x=m[++i];
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a=((a^a>>16)+m[i-ISAAC_SZ/2])&ISAAC_MASK;
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m[i]=y=(m[(x&(ISAAC_SZ-1)<<2)>>2]+a+b)&ISAAC_MASK;
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r[i]=b=(m[y>>(ISAAC_SZ_LOG+2)&(ISAAC_SZ-1)]+x)&ISAAC_MASK;
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}
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_ctx->b=b;
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_ctx->a=a;
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_ctx->n=ISAAC_SZ;
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}
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static void isaac_mix(unsigned _x[8]){
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static const unsigned char SHIFT[8]={11,2,8,16,10,4,8,9};
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int i;
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for(i=0;i<8;i++){
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_x[i]^=_x[(i+1)&7]<<SHIFT[i];
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_x[(i+3)&7]+=_x[i];
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_x[(i+1)&7]+=_x[(i+2)&7];
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i++;
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_x[i]^=_x[(i+1)&7]>>SHIFT[i];
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_x[(i+3)&7]+=_x[i];
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_x[(i+1)&7]+=_x[(i+2)&7];
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}
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}
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void isaac_init(isaac_ctx *_ctx,const void *_seed,int _nseed){
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const unsigned char *seed;
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unsigned *m;
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unsigned *r;
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unsigned x[8];
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int i;
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int j;
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_ctx->a=_ctx->b=_ctx->c=0;
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m=_ctx->m;
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r=_ctx->r;
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x[0]=x[1]=x[2]=x[3]=x[4]=x[5]=x[6]=x[7]=0x9E3779B9;
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for(i=0;i<4;i++)isaac_mix(x);
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if(_nseed>ISAAC_SEED_SZ_MAX)_nseed=ISAAC_SEED_SZ_MAX;
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seed=(const unsigned char *)_seed;
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for(i=0;i<_nseed>>2;i++){
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r[i]=seed[i<<2|3]<<24|seed[i<<2|2]<<16|seed[i<<2|1]<<8|seed[i<<2];
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}
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if(_nseed&3){
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r[i]=seed[i<<2];
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for(j=1;j<(_nseed&3);j++)r[i]+=seed[i<<2|j]<<(j<<3);
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i++;
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}
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memset(r+i,0,(ISAAC_SZ-i)*sizeof(*r));
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for(i=0;i<ISAAC_SZ;i+=8){
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for(j=0;j<8;j++)x[j]+=r[i+j];
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isaac_mix(x);
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memcpy(m+i,x,sizeof(x));
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}
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for(i=0;i<ISAAC_SZ;i+=8){
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for(j=0;j<8;j++)x[j]+=m[i+j];
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isaac_mix(x);
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memcpy(m+i,x,sizeof(x));
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}
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isaac_update(_ctx);
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}
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unsigned isaac_next_uint32(isaac_ctx *_ctx){
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if(!_ctx->n)isaac_update(_ctx);
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return _ctx->r[--_ctx->n];
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}
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/*Returns a uniform random integer less than the given maximum value.
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_n: The upper bound on the range of numbers returned (not inclusive).
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This must be strictly less than 2**32.
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Return: An integer uniformly distributed between 0 (inclusive) and _n
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(exclusive).*/
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unsigned isaac_next_uint(isaac_ctx *_ctx,unsigned _n){
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unsigned r;
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unsigned v;
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unsigned d;
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do{
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r=isaac_next_uint32(_ctx);
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v=r%_n;
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d=r-v;
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}
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while(((d+_n-1)&ISAAC_MASK)<d);
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return v;
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}
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