fw/random.c (af6f67d) - mips_sys · BlinkenArea

random.c

#include "random.h"

// FIXME: this random number generator is most likely not very good

/// state of the linear feedback shift register (LFSR)
static unsigned long random_lfsr = 1;

/// step LFSR
static void random_step(void)
{
  random_lfsr = (random_lfsr >> 1) ^ (-(random_lfsr & 1U) & 0xD0000001U);
}

/**
 * @brief provide entropy
 * @param[in] ptr pointer to buffer containing entropy
 * @param[in] sz size of buffer
 */
void random_provide_entropy(const void *ptr, unsigned int sz)
{
  const unsigned char *src = ptr;
  unsigned char val;
  unsigned int bit;

for ( ; sz > 0; --sz) {
    val = *src++;
    for (bit = 0; bit < 8; ++bit) {
      if (val & 1)
        random_step();
      val >>= 1;
    }
  }
}

/**
 * @brief get random data
 * @param[in] ptr pointer to buffer to fill with random data
 * @param[in] sz size of buffer to fill
 */
void random_get_data(void *ptr, unsigned int sz)
{
  unsigned char *dest = ptr;
  unsigned char val;
  unsigned int bit;

for ( ; sz > 0; --sz) {
    val = 0;
    for (bit = 0; bit < 8; ++bit) {
      random_step();
      val = val << 1 | (random_lfsr & 1);
    }
    *dest++ = val;
  }
}

mips_sys

implement basic pseudo random number generator