random: added random_bytes function

sys/include/random.h

@@ -27,6 +27,7 @@
 #define RANDOM_H
 
 #include <inttypes.h>
+#include <stddef.h>
 
 #ifdef __cplusplus
 extern "C" {
@@ -67,6 +68,11 @@ void random_init_by_array(uint32_t init_key[], int key_length);
  */
 uint32_t random_uint32(void);
 
+/**
+ * @brief writes random bytes in the [0,0xff]-interval to memory
+ */
+void random_bytes(uint8_t *buf, size_t size);
+
 /**
  * @brief   generates a random number r with a <= r < b.
  *

sys/random/tinymt32.c

@@ -6,7 +6,7 @@
  * directory for more details.
  */
 
- /**
+/**
  * @ingroup sys_random
  * @{
  * @file
@@ -20,9 +20,18 @@
  */
 
 #include <stdint.h>
+#include <string.h>
 
 #include "tinymt32/tinymt32.h"
 
+#define _ALIGNMENT_MASK (sizeof(uint32_t) - 1)
+
+/* fits size to byte alignment */
+static inline uint8_t *_align(uint8_t *buf)
+{
+    return (uint8_t *)(((size_t) buf + _ALIGNMENT_MASK) & ~(_ALIGNMENT_MASK));
+}
+
 static tinymt32_t _random;
 
 void random_init(uint32_t seed)
@@ -35,6 +44,36 @@ uint32_t random_uint32(void)
     return tinymt32_generate_uint32(&_random);
 }
 
+void random_bytes(uint8_t *buf, size_t size)
+{
+    size_t iter = size;
+    size_t diff = _align(buf) - buf;
+    uint32_t tmp;
+
+    /* Fill first <4 unaligned bytes */
+    if (diff) {
+        tmp = tinymt32_generate_uint32(&_random);
+        if (diff > size) {
+            diff = size;
+        }
+        memcpy(buf, &tmp, diff);
+        iter -= diff;
+    }
+
+    /* Fill aligned bytes */
+    while (iter >= sizeof(uint32_t)) {
+        *((uint32_t *) buf) = tinymt32_generate_uint32(&_random);
+        buf += sizeof(uint32_t);
+        iter -= sizeof(uint32_t);
+    }
+
+    /* Fill last bytes */
+    if (iter) {
+        tmp = tinymt32_generate_uint32(&_random);
+        memcpy(buf, &tmp, iter);
+    }
+}
+
 void random_init_by_array(uint32_t init_key[], int key_length)
 {
     tinymt32_init_by_array(&_random, init_key, key_length);