On Fri, Jul 31, 2015 at 04:54:00PM +0100, Alex Bennée wrote: > It's often useful to introduce some sort of random variation when > testing several racing CPU conditions. Instead of each test implementing > some half-arsed PRNG bring in a a decent one which has good statistical > randomness. Obviously it is deterministic for a given seed value which > is likely the behaviour you want. > > I've pulled in the ISAAC library from CCAN: > > http://ccodearchive.net/info/isaac.html > > I shaved off the float related stuff which is less useful for unit > testing and re-indented to fit the style. The original license was > CC0 (Public Domain) which is compatible with the LGPL v2 of > kvm-unit-tests. > > Signed-off-by: Alex Bennée <alex.bennee@xxxxxxxxxx> > CC: Timothy B. Terriberry <tterribe@xxxxxxxx> > --- > config/config-arm-common.mak | 1 + > lib/prng.c | 162 +++++++++++++++++++++++++++++++++++++++++++ > lib/prng.h | 82 ++++++++++++++++++++++ > 3 files changed, 245 insertions(+) > create mode 100644 lib/prng.c > create mode 100644 lib/prng.h > > diff --git a/config/config-arm-common.mak b/config/config-arm-common.mak > index 9c7607b..67a9dda 100644 > --- a/config/config-arm-common.mak > +++ b/config/config-arm-common.mak > @@ -34,6 +34,7 @@ cflatobjs += lib/devicetree.o > cflatobjs += lib/virtio.o > cflatobjs += lib/virtio-mmio.o > cflatobjs += lib/chr-testdev.o > +cflatobjs += lib/prng.o > cflatobjs += lib/arm/io.o > cflatobjs += lib/arm/setup.o > cflatobjs += lib/arm/mmu.o > diff --git a/lib/prng.c b/lib/prng.c > new file mode 100644 > index 0000000..ebd6df7 > --- /dev/null > +++ b/lib/prng.c > @@ -0,0 +1,162 @@ > +/* > + * Pseudo Random Number Generator > + * > + * Lifted from ccan modules ilog/isaac under CC0 > + * - http://ccodearchive.net/info/isaac.html > + * - http://ccodearchive.net/info/ilog.html > + * > + * And lightly hacked to compile under the KVM unit test environment. > + * This provides a handy RNG for torture tests that want to vary > + * delays and the like. > + * > + */ > + > +/*Written by Timothy B. Terriberry (tterribe@xxxxxxxx) 1999-2009. > + CC0 (Public domain) - see LICENSE file for details > + Based on the public domain implementation by Robert J. Jenkins Jr.*/ > + > +#include "libcflat.h" > + > +#include <string.h> > +#include "prng.h" > + > +#define ISAAC_MASK (0xFFFFFFFFU) > + > +/* Extract ISAAC_SZ_LOG bits (starting at bit 2). */ > +static inline uint32_t lower_bits(uint32_t x) > +{ > + return (x & ((ISAAC_SZ-1) << 2)) >> 2; > +} > + > +/* Extract next ISAAC_SZ_LOG bits (starting at bit ISAAC_SZ_LOG+2). */ > +static inline uint32_t upper_bits(uint32_t y) > +{ > + return (y >> (ISAAC_SZ_LOG+2)) & (ISAAC_SZ-1); > +} > + > +static void isaac_update(isaac_ctx *_ctx){ > + uint32_t *m; > + uint32_t *r; > + uint32_t a; > + uint32_t b; > + uint32_t x; > + uint32_t y; > + int i; > + m=_ctx->m; > + r=_ctx->r; > + a=_ctx->a; > + b=_ctx->b+(++_ctx->c); > + for(i=0;i<ISAAC_SZ/2;i++){ > + x=m[i]; > + a=(a^a<<13)+m[i+ISAAC_SZ/2]; > + m[i]=y=m[lower_bits(x)]+a+b; > + r[i]=b=m[upper_bits(y)]+x; > + x=m[++i]; > + a=(a^a>>6)+m[i+ISAAC_SZ/2]; > + m[i]=y=m[lower_bits(x)]+a+b; > + r[i]=b=m[upper_bits(y)]+x; > + x=m[++i]; > + a=(a^a<<2)+m[i+ISAAC_SZ/2]; > + m[i]=y=m[lower_bits(x)]+a+b; > + r[i]=b=m[upper_bits(y)]+x; > + x=m[++i]; > + a=(a^a>>16)+m[i+ISAAC_SZ/2]; > + m[i]=y=m[lower_bits(x)]+a+b; > + r[i]=b=m[upper_bits(y)]+x; > + } > + for(i=ISAAC_SZ/2;i<ISAAC_SZ;i++){ > + x=m[i]; > + a=(a^a<<13)+m[i-ISAAC_SZ/2]; > + m[i]=y=m[lower_bits(x)]+a+b; > + r[i]=b=m[upper_bits(y)]+x; > + x=m[++i]; > + a=(a^a>>6)+m[i-ISAAC_SZ/2]; > + m[i]=y=m[lower_bits(x)]+a+b; > + r[i]=b=m[upper_bits(y)]+x; > + x=m[++i]; > + a=(a^a<<2)+m[i-ISAAC_SZ/2]; > + m[i]=y=m[lower_bits(x)]+a+b; > + r[i]=b=m[upper_bits(y)]+x; > + x=m[++i]; > + a=(a^a>>16)+m[i-ISAAC_SZ/2]; > + m[i]=y=m[lower_bits(x)]+a+b; > + r[i]=b=m[upper_bits(y)]+x; > + } > + _ctx->b=b; > + _ctx->a=a; > + _ctx->n=ISAAC_SZ; > +} > + > +static void isaac_mix(uint32_t _x[8]){ > + static const unsigned char SHIFT[8]={11,2,8,16,10,4,8,9}; > + int i; > + for(i=0;i<8;i++){ > + _x[i]^=_x[(i+1)&7]<<SHIFT[i]; > + _x[(i+3)&7]+=_x[i]; > + _x[(i+1)&7]+=_x[(i+2)&7]; > + i++; > + _x[i]^=_x[(i+1)&7]>>SHIFT[i]; > + _x[(i+3)&7]+=_x[i]; > + _x[(i+1)&7]+=_x[(i+2)&7]; > + } > +} > + > + > +void isaac_init(isaac_ctx *_ctx,const unsigned char *_seed,int _nseed){ > + _ctx->a=_ctx->b=_ctx->c=0; > + memset(_ctx->r,0,sizeof(_ctx->r)); > + isaac_reseed(_ctx,_seed,_nseed); > +} > + > +void isaac_reseed(isaac_ctx *_ctx,const unsigned char *_seed,int _nseed){ > + uint32_t *m; > + uint32_t *r; > + uint32_t x[8]; > + int i; > + int j; > + m=_ctx->m; > + r=_ctx->r; > + if(_nseed>ISAAC_SEED_SZ_MAX)_nseed=ISAAC_SEED_SZ_MAX; > + for(i=0;i<_nseed>>2;i++){ > + r[i]^=(uint32_t)_seed[i<<2|3]<<24|(uint32_t)_seed[i<<2|2]<<16| > + (uint32_t)_seed[i<<2|1]<<8|_seed[i<<2]; > + } > + _nseed-=i<<2; > + if(_nseed>0){ > + uint32_t ri; > + ri=_seed[i<<2]; > + for(j=1;j<_nseed;j++)ri|=(uint32_t)_seed[i<<2|j]<<(j<<3); > + r[i++]^=ri; > + } > + x[0]=x[1]=x[2]=x[3]=x[4]=x[5]=x[6]=x[7]=0x9E3779B9U; > + for(i=0;i<4;i++)isaac_mix(x); > + for(i=0;i<ISAAC_SZ;i+=8){ > + for(j=0;j<8;j++)x[j]+=r[i+j]; > + isaac_mix(x); > + memcpy(m+i,x,sizeof(x)); > + } > + for(i=0;i<ISAAC_SZ;i+=8){ > + for(j=0;j<8;j++)x[j]+=m[i+j]; > + isaac_mix(x); > + memcpy(m+i,x,sizeof(x)); > + } > + isaac_update(_ctx); > +} > + > +uint32_t isaac_next_uint32(isaac_ctx *_ctx){ > + if(!_ctx->n)isaac_update(_ctx); > + return _ctx->r[--_ctx->n]; > +} > + > +uint32_t isaac_next_uint(isaac_ctx *_ctx,uint32_t _n){ > + uint32_t r; > + uint32_t v; > + uint32_t d; > + do{ > + r=isaac_next_uint32(_ctx); > + v=r%_n; > + d=r-v; > + } > + while(((d+_n-1)&ISAAC_MASK)<d); > + return v; > +} > diff --git a/lib/prng.h b/lib/prng.h > new file mode 100644 > index 0000000..bf5776d > --- /dev/null > +++ b/lib/prng.h > @@ -0,0 +1,82 @@ > +/* > + * PRNG Header > + */ > +#ifndef __PRNG_H__ > +#define __PRNG_H__ > + > +# include <stdint.h> > + > + > + > +typedef struct isaac_ctx isaac_ctx; > + > + > + > +/*This value may be lowered to reduce memory usage on embedded platforms, at > + the cost of reducing security and increasing bias. > + Quoting Bob Jenkins: "The current best guess is that bias is detectable after > + 2**37 values for [ISAAC_SZ_LOG]=3, 2**45 for 4, 2**53 for 5, 2**61 for 6, > + 2**69 for 7, and 2**77 values for [ISAAC_SZ_LOG]=8."*/ > +#define ISAAC_SZ_LOG (8) > +#define ISAAC_SZ (1<<ISAAC_SZ_LOG) > +#define ISAAC_SEED_SZ_MAX (ISAAC_SZ<<2) > + > + > + > +/*ISAAC is the most advanced of a series of pseudo-random number generators > + designed by Robert J. Jenkins Jr. in 1996. > + http://www.burtleburtle.net/bob/rand/isaac.html > + To quote: > + No efficient method is known for deducing their internal states. > + ISAAC requires an amortized 18.75 instructions to produce a 32-bit value. > + There are no cycles in ISAAC shorter than 2**40 values. > + The expected cycle length is 2**8295 values.*/ > +struct isaac_ctx{ > + unsigned n; > + uint32_t r[ISAAC_SZ]; > + uint32_t m[ISAAC_SZ]; > + uint32_t a; > + uint32_t b; > + uint32_t c; > +}; > + > + > +/** > + * isaac_init - Initialize an instance of the ISAAC random number generator. > + * @_ctx: The instance to initialize. > + * @_seed: The specified seed bytes. > + * This may be NULL if _nseed is less than or equal to zero. > + * @_nseed: The number of bytes to use for the seed. > + * If this is greater than ISAAC_SEED_SZ_MAX, the extra bytes are > + * ignored. > + */ > +void isaac_init(isaac_ctx *_ctx,const unsigned char *_seed,int _nseed); > + > +/** > + * isaac_reseed - Mix a new batch of entropy into the current state. > + * To reset ISAAC to a known state, call isaac_init() again instead. > + * @_ctx: The instance to reseed. > + * @_seed: The specified seed bytes. > + * This may be NULL if _nseed is zero. > + * @_nseed: The number of bytes to use for the seed. > + * If this is greater than ISAAC_SEED_SZ_MAX, the extra bytes are > + * ignored. > + */ > +void isaac_reseed(isaac_ctx *_ctx,const unsigned char *_seed,int _nseed); > +/** > + * isaac_next_uint32 - Return the next random 32-bit value. > + * @_ctx: The ISAAC instance to generate the value with. > + */ > +uint32_t isaac_next_uint32(isaac_ctx *_ctx); > +/** > + * isaac_next_uint - Uniform random integer less than the given value. > + * @_ctx: The ISAAC instance to generate the value with. > + * @_n: The upper bound on the range of numbers returned (not inclusive). > + * This must be greater than zero and less than 2**32. > + * To return integers in the full range 0...2**32-1, use > + * isaac_next_uint32() instead. > + * Return: An integer uniformly distributed between 0 and _n-1 (inclusive). > + */ > +uint32_t isaac_next_uint(isaac_ctx *_ctx,uint32_t _n); > + > +#endif > -- > 2.5.0 > > Agreed that (pseudo) random numbers could be useful in unit tests. Acked-by: Andrew Jones <drjones@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
