Introduce a random module that is a subset of CPython's random. It

also initializes in the same way where it takes from a true random
source when available through os.urandom(). After initializing, it
produces deterministic results until the seed is set.

This replaces urandom!

Fixes #139.

12 files changed, 416 insertions, 11 deletions

diff --git a/atmel-samd/Makefile b/atmel-samd/Makefile
index 239c80189..ec8cd9b26 100644
--- a/atmel-samd/Makefile
+++ b/atmel-samd/Makefile
@@ -272,6 +272,7 @@ SRC_SHARED_MODULE = \
 	bitbangio/SPI.c \
 	busio/OneWire.c \
 	os/__init__.c \
+	random/__init__.c \
 	storage/__init__.c \
 	uheap/__init__.c \
 
diff --git a/atmel-samd/common-hal/os/__init__.c b/atmel-samd/common-hal/os/__init__.c
index 2d2067ee0..2df4e40ff 100644
--- a/atmel-samd/common-hal/os/__init__.c
+++ b/atmel-samd/common-hal/os/__init__.c
@@ -55,3 +55,7 @@ STATIC MP_DEFINE_ATTRTUPLE(
 mp_obj_t common_hal_os_uname(void) {
     return (mp_obj_t)&os_uname_info_obj;
 }
+
+bool common_hal_os_urandom(uint8_t* buffer, uint32_t length) {
+    return false;
+}
diff --git a/atmel-samd/mpconfigport.h b/atmel-samd/mpconfigport.h
index 06e789ed1..228518a1e 100644
--- a/atmel-samd/mpconfigport.h
+++ b/atmel-samd/mpconfigport.h
@@ -57,8 +57,8 @@
 #define MICROPY_PY_MATH             (1)
 #define MICROPY_PY_CMATH            (0)
 #define MICROPY_PY_IO               (0)
-#define MICROPY_PY_URANDOM          (1)
-#define MICROPY_PY_URANDOM_EXTRA_FUNCS (1)
+#define MICROPY_PY_URANDOM          (0)
+#define MICROPY_PY_URANDOM_EXTRA_FUNCS (0)
 #define MICROPY_PY_STRUCT           (1)
 #define MICROPY_PY_SYS              (1)
 #define MICROPY_CPYTHON_COMPAT      (0)
@@ -138,6 +138,7 @@ extern const struct _mp_obj_module_t pulseio_module;
 extern const struct _mp_obj_module_t busio_module;
 extern const struct _mp_obj_module_t board_module;
 extern const struct _mp_obj_module_t os_module;
+extern const struct _mp_obj_module_t random_module;
 extern const struct _mp_obj_module_t storage_module;
 extern const struct _mp_obj_module_t time_module;
 extern const struct _mp_obj_module_t neopixel_write_module;
@@ -176,6 +177,7 @@ extern const struct _mp_obj_module_t usb_hid_module;
     { MP_OBJ_NEW_QSTR(MP_QSTR_busio), (mp_obj_t)&busio_module }, \
     { MP_OBJ_NEW_QSTR(MP_QSTR_board), (mp_obj_t)&board_module }, \
     { MP_OBJ_NEW_QSTR(MP_QSTR_os), (mp_obj_t)&os_module }, \
+    { MP_OBJ_NEW_QSTR(MP_QSTR_random), (mp_obj_t)&random_module }, \
     { MP_OBJ_NEW_QSTR(MP_QSTR_storage), (mp_obj_t)&storage_module }, \
     { MP_OBJ_NEW_QSTR(MP_QSTR_time), (mp_obj_t)&time_module }, \
     { MP_OBJ_NEW_QSTR(MP_QSTR_neopixel_write),(mp_obj_t)&neopixel_write_module }, \
diff --git a/esp8266/Makefile b/esp8266/Makefile
index 54c826351..168e74383 100644
--- a/esp8266/Makefile
+++ b/esp8266/Makefile
@@ -139,6 +139,7 @@ SRC_SHARED_MODULE = \
 	busio/I2C.c \
 	busio/OneWire.c \
 	os/__init__.c \
+	random/__init__.c \
 	storage/__init__.c \
 
 SRC_SHARED_MODULE_EXPANDED = $(addprefix shared-bindings/, $(SRC_SHARED_MODULE)) \
diff --git a/esp8266/common-hal/os/__init__.c b/esp8266/common-hal/os/__init__.c
index df241ecae..4f82a79e0 100644
--- a/esp8266/common-hal/os/__init__.c
+++ b/esp8266/common-hal/os/__init__.c
@@ -27,6 +27,7 @@
 
 #include <string.h>
 
+#include "etshal.h"
 #include "py/objtuple.h"
 #include "py/objstr.h"
 #include "genhdr/mpversion.h"
@@ -60,3 +61,20 @@ mp_obj_t common_hal_os_uname(void) {
     os_uname_info_obj.items[2] = mp_obj_new_str(ver, strlen(ver), false);
     return (mp_obj_t)&os_uname_info_obj;
 }
+
+static uint32_t last_random;
+bool common_hal_os_urandom(uint8_t* buffer, uint32_t length) {
+    uint32_t i = 0;
+    while (i < length) {
+        uint32_t new_random = last_random;
+        while (new_random == last_random) {
+            new_random = *WDEV_HWRNG;
+        }
+        for (int j = 0; j < 4 && i < length; j++) {
+            buffer[i] = new_random & 0xff;
+            i++;
+            new_random >>= 8;
+        }
+    }
+    return true;
+}
diff --git a/esp8266/mpconfigport.h b/esp8266/mpconfigport.h
index 066788832..faff05bba 100644
--- a/esp8266/mpconfigport.h
+++ b/esp8266/mpconfigport.h
@@ -68,7 +68,7 @@
 #define MICROPY_PY_UHEAPQ           (1)
 #define MICROPY_PY_UTIMEQ           (1)
 #define MICROPY_PY_UJSON            (1)
-#define MICROPY_PY_URANDOM          (1)
+#define MICROPY_PY_URANDOM          (0)
 #define MICROPY_PY_URE              (1)
 #define MICROPY_PY_USELECT          (1)
 #define MICROPY_PY_UTIME_MP_HAL     (1)
@@ -155,8 +155,8 @@ void *esp_native_code_commit(void*, size_t);
 // extra built in modules to add to the list of known ones
 extern const struct _mp_obj_module_t esp_module;
 extern const struct _mp_obj_module_t network_module;
-extern const struct _mp_obj_module_t utime_module;
 extern const struct _mp_obj_module_t os_module;
+extern const struct _mp_obj_module_t random_module;
 extern const struct _mp_obj_module_t storage_module;
 extern const struct _mp_obj_module_t mp_module_lwip;
 extern const struct _mp_obj_module_t mp_module_machine;
@@ -186,6 +186,7 @@ extern const struct _mp_obj_module_t time_module;
     { MP_OBJ_NEW_QSTR(MP_QSTR_busio), (mp_obj_t)&busio_module }, \
     { MP_OBJ_NEW_QSTR(MP_QSTR_bitbangio), (mp_obj_t)&bitbangio_module }, \
     { MP_OBJ_NEW_QSTR(MP_QSTR_storage), (mp_obj_t)&storage_module }, \
+    { MP_OBJ_NEW_QSTR(MP_QSTR_random), (mp_obj_t)&random_module }, \
     { MP_OBJ_NEW_QSTR(MP_QSTR_time), (mp_obj_t)&time_module }, \
 
 #define MICROPY_PORT_BUILTIN_MODULE_WEAK_LINKS \
diff --git a/shared-bindings/index.rst b/shared-bindings/index.rst
index 918fb5675..4c0741554 100644
--- a/shared-bindings/index.rst
+++ b/shared-bindings/index.rst
@@ -12,13 +12,13 @@ limited. For example, a microcontroller without analog features will not have
 Support Matrix
 ---------------
 
-===============  ==========  =========  ===========  =======  =======  ===========  =================  ================  =======  =========  =========  ========  =========  =======  =========
-Port             `analogio`  `audioio`  `bitbangio`  `board`  `busio`  `digitalio`  `microcontroller`  `neopixel_write`  `os`     `pulseio`  `storage`  `time`    `touchio`  `uheap`  `usb_hid`
-===============  ==========  =========  ===========  =======  =======  ===========  =================  ================  =======  =========  =========  ========  =========  =======  =========
-SAMD21           **Yes**     No         No           **Yes**  **Yes**  **Yes**      **Yes**            **Yes**           **Yes**  No         **Yes**    **Yes**   **Yes**    Debug    **Yes**
-SAMD21 Express   **Yes**     **Yes**    **Yes**      **Yes**  **Yes**  **Yes**      **Yes**            **Yes**           **Yes**  **Yes**    **Yes**    **Yes**   **Yes**    Debug    **Yes**
-ESP8266          **Yes**     No         **Yes**      **Yes**  **Yes**  **Yes**      **Yes**            **Yes**           **Yes**  No         **Yes**    **Yes**   No         Debug    No
-===============  ==========  =========  ===========  =======  =======  ===========  =================  ================  =======  =========  =========  ========  =========  =======  =========
+===============  ==========  =========  ===========  =======  =======  ===========  =================  ================  =======  =========  ========  =========  ========  =========  =======  =========
+Port             `analogio`  `audioio`  `bitbangio`  `board`  `busio`  `digitalio`  `microcontroller`  `neopixel_write`  `os`     `pulseio`  `random`  `storage`  `time`    `touchio`  `uheap`  `usb_hid`
+===============  ==========  =========  ===========  =======  =======  ===========  =================  ================  =======  =========  ========  =========  ========  =========  =======  =========
+SAMD21           **Yes**     No         No           **Yes**  **Yes**  **Yes**      **Yes**            **Yes**           **Yes**  No         **Yes**   **Yes**    **Yes**   **Yes**    Debug    **Yes**
+SAMD21 Express   **Yes**     **Yes**    **Yes**      **Yes**  **Yes**  **Yes**      **Yes**            **Yes**           **Yes**  **Yes**    **Yes**   **Yes**    **Yes**   **Yes**    Debug    **Yes**
+ESP8266          **Yes**     No         **Yes**      **Yes**  **Yes**  **Yes**      **Yes**            **Yes**           **Yes**  No         **Yes**   **Yes**    **Yes**   No         Debug    No
+===============  ==========  =========  ===========  =======  =======  ===========  =================  ================  =======  =========  ========  =========  ========  =========  =======  =========
 
 Modules
 ---------
diff --git a/shared-bindings/os/__init__.c b/shared-bindings/os/__init__.c
index 6185f0bf2..277224538 100644
--- a/shared-bindings/os/__init__.c
+++ b/shared-bindings/os/__init__.c
@@ -33,6 +33,7 @@
 #include "lib/oofatfs/diskio.h"
 #include "py/mpstate.h"
 #include "py/obj.h"
+#include "py/runtime.h"
 #include "shared-bindings/os/__init__.h"
 
 //| :mod:`os` --- functions that an OS normally provides
@@ -187,6 +188,20 @@ STATIC mp_obj_t os_sync(void) {
 }
 MP_DEFINE_CONST_FUN_OBJ_0(os_sync_obj, os_sync);
 
+//| .. function:: urandom(size)
+//|
+//|   Returns a string of *size* random bytes based on a hardware True Random
+//|   Number Generator. When not available, it will raise a NotImplementedError.
+//|
+STATIC mp_obj_t os_urandom(mp_obj_t size_in) {
+    mp_int_t size = mp_obj_get_int(size_in);
+    uint8_t tmp[size];
+    if (!common_hal_os_urandom(tmp, size)) {
+        mp_raise_NotImplementedError("");
+    }
+    return mp_obj_new_bytes(tmp, size);
+}
+MP_DEFINE_CONST_FUN_OBJ_1(os_urandom_obj, os_urandom);
 
 STATIC const mp_rom_map_elem_t os_module_globals_table[] = {
     { MP_OBJ_NEW_QSTR(MP_QSTR___name__), MP_OBJ_NEW_QSTR(MP_QSTR_os) },
@@ -206,6 +221,8 @@ STATIC const mp_rom_map_elem_t os_module_globals_table[] = {
 
     { MP_OBJ_NEW_QSTR(MP_QSTR_sync), MP_ROM_PTR(&os_sync_obj) },
 
+    { MP_OBJ_NEW_QSTR(MP_QSTR_urandom), MP_ROM_PTR(&os_urandom_obj) },
+
 //| .. data:: sep
 //|
 //|   Separator used to dileneate path components such as folder and file names.
diff --git a/shared-bindings/os/__init__.h b/shared-bindings/os/__init__.h
index e04a39319..41715e7ac 100644
--- a/shared-bindings/os/__init__.h
+++ b/shared-bindings/os/__init__.h
@@ -45,4 +45,7 @@ void common_hal_os_rmdir(const char* path);
 mp_obj_t common_hal_os_stat(const char* path);
 mp_obj_t common_hal_os_statvfs(const char* path);
 
+// Returns true if data was correctly sourced from a true random number generator.
+bool common_hal_os_urandom(uint8_t* buffer, mp_uint_t length);
+
 #endif  // __MICROPY_INCLUDED_SHARED_BINDINGS_OS___INIT___H__
diff --git a/shared-bindings/random/__init__.c b/shared-bindings/random/__init__.c
new file mode 100644
index 000000000..fe52c1fc0
--- /dev/null
+++ b/shared-bindings/random/__init__.c
@@ -0,0 +1,188 @@
+/*
+ * This file is part of the Micro Python project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016 Paul Sokolovsky
+ * Copyright (c) 2016 Scott Shawcroft for Adafruit Industries
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <assert.h>
+#include <string.h>
+
+#include "py/obj.h"
+#include "py/runtime.h"
+#include "shared-bindings/random/__init__.h"
+
+//| :mod:`random` --- psuedo-random numbers and choices
+//| ========================================================
+//|
+//| .. module:: random
+//|   :synopsis: psuedo-random numbers and choices
+//|   :platform: SAMD21, ESP8266
+//|
+//| The `random` module is a strict subset of the CPython `cpython:random`
+//| module. So, code written in CircuitPython will work in CPython but not
+//| necessarily the other way around.
+//|
+//| Like its CPython cousin, CircuitPython's random seeds itself on first use
+//| with a true random from os.urandom() when available or the uptime otherwise.
+//| Once seeded, it will be deterministic, which is why its bad for cryptography.
+//|
+//| .. warning:: Numbers from this module are not cryptographically strong! Use
+//|   bytes from `os.urandom` directly for true randomness.
+//|
+
+//| .. function:: seed(seed)
+//|
+//|   Sets the starting seed of the random  number generation. Further calls to
+//|   `random` will return deterministic results afterwards.
+//|
+STATIC mp_obj_t random_seed(mp_obj_t seed_in) {
+    mp_uint_t seed = mp_obj_get_int_truncated(seed_in);
+    shared_modules_random_seed(seed);
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(random_seed_obj, random_seed);
+
+//| .. function:: getrandbits(k)
+//|
+//|   Returns an integer with *k* random bits.
+//|
+STATIC mp_obj_t random_getrandbits(mp_obj_t num_in) {
+    int n = mp_obj_get_int(num_in);
+    if (n > 32 || n == 0) {
+        mp_raise_ValueError(NULL);
+    }
+    return mp_obj_new_int_from_uint(shared_modules_random_getrandbits((uint8_t) n));
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(random_getrandbits_obj, random_getrandbits);
+
+//| .. function:: randrange(stop)
+//|               randrange(start, stop, step=1)
+//|
+//|   Returns a randomly selected integer from `range(start, stop, step)`.
+//|
+STATIC mp_obj_t random_randrange(size_t n_args, const mp_obj_t *args) {
+    mp_int_t start = 0;
+    mp_int_t stop = mp_obj_get_int(args[0]);
+    mp_int_t step = 1;
+    if (n_args == 1) {
+        // range(stop)
+        if (stop <= 0) {
+            mp_raise_ValueError("stop not reachable from start");
+        }
+    } else {
+        start = stop;
+        stop = mp_obj_get_int(args[1]);
+        if (n_args == 2) {
+            // range(start, stop)
+            if (start >= stop) {
+                mp_raise_ValueError("stop not reachable from start");
+            }
+        } else {
+            // range(start, stop, step)
+            step = mp_obj_get_int(args[2]);
+            mp_int_t n;
+            if (step > 0) {
+                n = (stop - start + step - 1) / step;
+            } else if (step < 0) {
+                n = (stop - start + step + 1) / step;
+            } else {
+                mp_raise_ValueError("step must be non-zero");
+            }
+            if (n <= 0) {
+                mp_raise_ValueError("invalid step");
+            }
+        }
+    }
+
+    return mp_obj_new_int(shared_modules_random_randrange(start, stop, step));
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(random_randrange_obj, 1, 3, random_randrange);
+
+//| .. function:: randint(a, b)
+//|
+//|   Returns a randomly selected integer between a and b inclusive. Equivalent
+//|   to `randrange(a, b + 1, 1)`
+//|
+STATIC mp_obj_t random_randint(mp_obj_t a_in, mp_obj_t b_in) {
+    mp_int_t a = mp_obj_get_int(a_in);
+    mp_int_t b = mp_obj_get_int(b_in);
+    if (a > b) {
+        mp_raise_ValueError(NULL);
+    }
+    return mp_obj_new_int(shared_modules_random_randrange(a, b + 1, 1));
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_2(random_randint_obj, random_randint);
+
+//| .. function:: choice(seq)
+//|
+//|   Returns a randomly selected element from the given sequence. Raises
+//|   IndexError when the sequence is empty.
+//|
+STATIC mp_obj_t random_choice(mp_obj_t seq) {
+    mp_int_t len = mp_obj_get_int(mp_obj_len(seq));
+    if (len == 0) {
+        mp_raise_IndexError("empty sequence");
+    }
+    return mp_obj_subscr(seq, mp_obj_new_int(shared_modules_random_randrange(0, len, 1)), MP_OBJ_SENTINEL);
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(random_choice_obj, random_choice);
+
+//| .. function:: random()
+//|
+//|   Returns a random float between 0 and 1.0.
+//|
+STATIC mp_obj_t random_random(void) {
+    return mp_obj_new_float(shared_modules_random_random());
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_0(random_random_obj, random_random);
+
+//| .. function:: uniform(a, b)
+//|
+//|   Returns a random float between a and b. It may or may not be inclusive
+//|   depending on float rounding.
+//|
+STATIC mp_obj_t random_uniform(mp_obj_t a_in, mp_obj_t b_in) {
+    mp_float_t a = mp_obj_get_float(a_in);
+    mp_float_t b = mp_obj_get_float(b_in);
+    return mp_obj_new_float(shared_modules_random_uniform(a, b));
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_2(random_uniform_obj, random_uniform);
+
+STATIC const mp_rom_map_elem_t mp_module_random_globals_table[] = {
+    { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_random) },
+    { MP_ROM_QSTR(MP_QSTR_seed), MP_ROM_PTR(&random_seed_obj) },
+    { MP_ROM_QSTR(MP_QSTR_getrandbits), MP_ROM_PTR(&random_getrandbits_obj) },
+    { MP_ROM_QSTR(MP_QSTR_randrange), MP_ROM_PTR(&random_randrange_obj) },
+    { MP_ROM_QSTR(MP_QSTR_randint), MP_ROM_PTR(&random_randint_obj) },
+    { MP_ROM_QSTR(MP_QSTR_choice), MP_ROM_PTR(&random_choice_obj) },
+    { MP_ROM_QSTR(MP_QSTR_random), MP_ROM_PTR(&random_random_obj) },
+    { MP_ROM_QSTR(MP_QSTR_uniform), MP_ROM_PTR(&random_uniform_obj) },
+};
+
+STATIC MP_DEFINE_CONST_DICT(mp_module_random_globals, mp_module_random_globals_table);
+
+const mp_obj_module_t random_module = {
+    .base = { &mp_type_module },
+    .globals = (mp_obj_dict_t*)&mp_module_random_globals,
+};
diff --git a/shared-bindings/random/__init__.h b/shared-bindings/random/__init__.h
new file mode 100644
index 000000000..558b5f194
--- /dev/null
+++ b/shared-bindings/random/__init__.h
@@ -0,0 +1,40 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2017 Scott Shawcroft for Adafruit Industries
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef __MICROPY_INCLUDED_SHARED_BINDINGS_RANDOM___INIT___H__
+#define __MICROPY_INCLUDED_SHARED_BINDINGS_RANDOM___INIT___H__
+
+// This depends on shared_module because nearly all functionality is port
+// agnostic. The random module only depends on the common_hal_os_urandom or
+// common_hal_time_monotonic to seed it initially.
+
+void shared_modules_random_seed(mp_uint_t seed);
+mp_uint_t shared_modules_random_getrandbits(uint8_t n);
+mp_int_t shared_modules_random_randrange(mp_int_t start, mp_int_t stop, mp_int_t step);
+mp_float_t shared_modules_random_random(void);
+mp_float_t shared_modules_random_uniform(mp_float_t a, mp_float_t b);
+
+#endif  // __MICROPY_INCLUDED_SHARED_BINDINGS_RANDOM___INIT___H__
diff --git a/shared-module/random/__init__.c b/shared-module/random/__init__.c
new file mode 100644
index 000000000..5cc20e5b5
--- /dev/null
+++ b/shared-module/random/__init__.c
@@ -0,0 +1,130 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016 Paul Sokolovsky
+ * Copyright (c) 2017 Scott Shawcroft for Adafruit Industries
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <assert.h>
+#include <string.h>
+
+#include "py/runtime.h"
+#include "shared-bindings/os/__init__.h"
+#include "shared-bindings/time/__init__.h"
+
+// Yasmarang random number generator
+// by Ilya Levin
+// http://www.literatecode.com/yasmarang
+// Public Domain
+
+STATIC uint32_t yasmarang_pad = 0xeda4baba, yasmarang_n = 69, yasmarang_d = 233;
+STATIC uint8_t yasmarang_dat = 0;
+
+STATIC uint32_t yasmarang(void)
+{
+    if (yasmarang_pad == 0xeda4baba) {
+        if (!common_hal_os_urandom((uint8_t *)&yasmarang_pad, sizeof(uint32_t))) {
+            yasmarang_pad = common_hal_time_monotonic() & 0xffffffff;
+        }
+    }
+   yasmarang_pad += yasmarang_dat + yasmarang_d * yasmarang_n;
+   yasmarang_pad = (yasmarang_pad<<3) + (yasmarang_pad>>29);
+   yasmarang_n = yasmarang_pad | 2;
+   yasmarang_d ^= (yasmarang_pad<<31) + (yasmarang_pad>>1);
+   yasmarang_dat ^= (char) yasmarang_pad ^ (yasmarang_d>>8) ^ 1;
+
+   return (yasmarang_pad^(yasmarang_d<<5)^(yasmarang_pad>>18)^(yasmarang_dat<<1));
+}  /* yasmarang */
+
+// End of Yasmarang
+
+// returns an unsigned integer below the given argument
+// n must not be zero
+STATIC uint32_t yasmarang_randbelow(uint32_t n) {
+    uint32_t mask = 1;
+    while ((n & mask) < n) {
+        mask = (mask << 1) | 1;
+    }
+    uint32_t r;
+    do {
+        r = yasmarang() & mask;
+    } while (r >= n);
+    return r;
+}
+
+void shared_modules_random_seed(mp_uint_t seed) {
+    yasmarang_pad = seed;
+    yasmarang_n = 69;
+    yasmarang_d = 233;
+    yasmarang_dat = 0;
+}
+
+mp_uint_t shared_modules_random_getrandbits(uint8_t n) {
+    uint32_t mask = ~0;
+    // Beware of C undefined behavior when shifting by >= than bit size
+    mask >>= (32 - n);
+    return yasmarang() & mask;
+}
+
+mp_int_t shared_modules_random_randrange(mp_int_t start, mp_int_t stop, mp_int_t step) {
+    mp_int_t n;
+    if (step > 0) {
+        n = (stop - start + step - 1) / step;
+    } else {
+        n = (stop - start + step + 1) / step;
+    }
+    return start + step * yasmarang_randbelow(n);
+}
+
+// returns a number in the range [0..1) using Yasmarang to fill in the fraction bits
+STATIC mp_float_t yasmarang_float(void) {
+    #if MICROPY_FLOAT_IMPL == MICROPY_FLOAT_IMPL_DOUBLE
+    typedef uint64_t mp_float_int_t;
+    #elif MICROPY_FLOAT_IMPL == MICROPY_FLOAT_IMPL_FLOAT
+    typedef uint32_t mp_float_int_t;
+    #endif
+    union {
+        mp_float_t f;
+        #if MP_ENDIANNESS_LITTLE
+        struct { mp_float_int_t frc:MP_FLOAT_FRAC_BITS, exp:MP_FLOAT_EXP_BITS, sgn:1; } p;
+        #else
+        struct { mp_float_int_t sgn:1, exp:MP_FLOAT_EXP_BITS, frc:MP_FLOAT_FRAC_BITS; } p;
+        #endif
+    } u;
+    u.p.sgn = 0;
+    u.p.exp = (1 << (MP_FLOAT_EXP_BITS - 1)) - 1;
+    if (MP_FLOAT_FRAC_BITS <= 32) {
+        u.p.frc = yasmarang();
+    } else {
+        u.p.frc = ((uint64_t)yasmarang() << 32) | (uint64_t)yasmarang();
+    }
+    return u.f - 1;
+}
+
+mp_float_t shared_modules_random_random(void) {
+    return yasmarang_float();
+}
+
+mp_float_t shared_modules_random_uniform(mp_float_t a, mp_float_t b) {
+    return a + (b - a) * yasmarang_float();
+}