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Make xorshift128 re-entrant so that we do do have to suffer the overhad of serialization controls.

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This commit is contained in:
Gregory Nutt
2016-08-21 07:47:53 -06:00
parent 757023a909
commit 60b70f7dbb
4 changed files with 91 additions and 143 deletions
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libc/misc/lib_xorshift128.c
+20 -92
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@@ -43,10 +43,11 @@
#include <nuttx/config.h>
#include <sys/types.h>
#include <stdint.h>
#include <sched.h>
#include <assert.h>
#include <nuttx/irq.h>
#include <nuttx/lib/xorshift128.h>
/****************************************************************************
* Private Types
@@ -56,119 +57,46 @@
# define CONFIG_CPULOAD_ONESHOT_ENTROPY 0
#endif
/****************************************************************************
* Private Types
****************************************************************************/
struct xorshift128_state_s
{
uint32_t x;
uint32_t y;
uint32_t z;
uint32_t w;
};
/****************************************************************************
* Private Data
****************************************************************************/
static struct xorshift128_state_s g_prng;
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: xorshift128_seed
*
* Description:
* Seed the XorShift128 PRNG
*
* Input Parameters:
* w, x, y, z: Values for XorShift128 generation state.
*
* Returned Value:
* No
*
****************************************************************************/
void xorshift128_seed(uint32_t w, uint32_t x, uint32_t y, uint32_t z)
{
/* With CONFIG_CPULOAD_ONESHOT_ENTROPY > 0, this PRNG could be called from
* the interrupt handling state (currently is not).
*/
#if CONFIG_CPULOAD_ONESHOT_ENTROPY > 0
irqstate_t flags;
flags = enter_critical_section();
#else
sched_lock();
#endif
/* Seed the PRNG */
g_prng.w = w;
g_prng.x = x;
g_prng.y = y;
g_prng.z = z;
#if CONFIG_CPULOAD_ONESHOT_ENTROPY > 0
leave_critical_section(flags);
#else
sched_unlock();
#endif
}
/****************************************************************************
* Name: xorshift128
*
* Description:
* Generate one 32-bit pseudo-random number
* Generate one 32-bit pseudo-random number.
*
* NOTE: Because the PRNG state is passed as a parameter, this function is
* fully re-entrant and may be called from an interrupt handler.
*
* The downside to this is that users of the PRNG might not get as much
* entropy as if it were a common state structure.
*
* Input Parameters:
* None
* state - The current XorShift128 state.
*
* Returned Value:
* The generated pseudo-random number
*
****************************************************************************/
uint32_t xorshift128(void)
uint32_t xorshift128(FAR struct xorshift128_state_s *state)
{
uint32_t ret;
uint32_t t;
/* With CONFIG_CPULOAD_ONESHOT_ENTROPY > 0, this PRNG will be called from
* the interrupt handling state.
*/
DEBUGASSERT(state != NULL);
#if CONFIG_CPULOAD_ONESHOT_ENTROPY > 0
irqstate_t flags;
flags = enter_critical_section();
#else
sched_lock();
#endif
t = g_prng.x;
t = state->x;
t ^= t << 11;
t ^= t >> 8;
g_prng.x = g_prng.y;
g_prng.y = g_prng.z;
g_prng.z = g_prng.w;
state->x = state->y;
state->y = state->z;
state->z = state->w;
g_prng.w ^= g_prng.w >> 19;
g_prng.w ^= t;
state->w ^= state->w >> 19;
state->w ^= t;
ret = g_prng.w;
#if CONFIG_CPULOAD_ONESHOT_ENTROPY > 0
leave_critical_section(flags);
#else
sched_unlock();
#endif
return ret;
return state->w;
}