mips_sys

implement basic pseudo random number generator
Parent c89d999
Stefan Schuermans

Stefan Schuermans commited on 2012-04-04 22:27:02
Showing 2 changed files, with 74 additions and 0 deletions.

fw/random.c
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+#include "random.h"
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+
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+// FIXME: this random number generator is most likely not very good
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+
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+/// state of the linear feedback shift register (LFSR)
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+static unsigned long random_lfsr = 1;
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+
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+/// step LFSR
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+static void random_step(void)
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+{
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+  random_lfsr = (random_lfsr >> 1) ^ (-(random_lfsr & 1U) & 0xD0000001U);
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+}
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+
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+/**
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+ * @brief provide entropy
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+ * @param[in] ptr pointer to buffer containing entropy
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+ * @param[in] sz size of buffer
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+ */
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+void random_provide_entropy(const void *ptr, unsigned int sz)
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+{
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+  const unsigned char *src = ptr;
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+  unsigned char val;
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+  unsigned int bit;
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+
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+  for ( ; sz > 0; --sz) {
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+    val = *src++;
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+    for (bit = 0; bit < 8; ++bit) {
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+      if (val & 1)
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+        random_step();
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+      val >>= 1;
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+    }
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+  }
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+}
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+
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+/**
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+ * @brief get random data
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+ * @param[in] ptr pointer to buffer to fill with random data
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+ * @param[in] sz size of buffer to fill
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+ */
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+void random_get_data(void *ptr, unsigned int sz)
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+{
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+  unsigned char *dest = ptr;
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+  unsigned char val;
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+  unsigned int bit;
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+
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+  for ( ; sz > 0; --sz) {
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+    val = 0;
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+    for (bit = 0; bit < 8; ++bit) {
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+      random_step();
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+      val = val << 1 | (random_lfsr & 1);
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+    }
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+    *dest++ = val;
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+  }
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+}
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+
fw/random.h
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+#ifndef RANDOM_H
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+#define RANDOM_H
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+
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+/**
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+ * @brief provide entropy
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+ * @param[in] ptr pointer to buffer containing entropy
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+ * @param[in] sz size of buffer
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+ */
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+void random_provide_entropy(const void *ptr, unsigned int sz);
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+
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+/**
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+ * @brief get random data
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+ * @param[in] ptr pointer to buffer to fill with random data
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+ * @param[in] sz size of buffer to fill
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+ */
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+void random_get_data(void *ptr, unsigned int sz);
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+
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+#endif // #ifdef RANDOM_H
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+
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