cython translation of dns_random.c

coro/dns/surf.pyx

+# -*- Mode: Cython -*-
+
+from libc.stdint cimport uint32_t, uint8_t
+
+# cython translation of Eric Huss' version of djb's dns_random.c
+
+# crummy emulation of the C macros
+cdef inline uint32_t ROTATE (uint32_t x, uint32_t b):
+    return (((x) << (b)) | ((x) >> (32 - (b))))
+
+cdef inline void MUSH (uint32_t i, uint32_t b, uint32_t *x, uint32_t *t, uint32_t s):
+    t[i] += (((x[0] ^ seed[i]) + s) ^ ROTATE (x[0], b))
+    x[0] = t[i]
+
+cdef uint32_t seed[32]
+cdef uint32_t iin[12]
+cdef uint32_t out[8]
+cdef int outleft = 0
+
+#
+#  Simple Unpredictable Random Function
+#
+cdef surf():
+    cdef uint32_t t[12], x, sum = 0
+    cdef int r, i, loop
+    for i in range (12):
+        t[i] = iin[i] ^ seed[12 + i]
+    for i in range (8):
+        out[i] = seed[24 + i]
+    x = t[11]
+    for loop in range (2):
+        for r in range (16):
+            sum += 0x9e3779b9U
+            MUSH(0,5,&x,t,sum)
+            MUSH(1,7,&x,t,sum)
+            MUSH(2,9,&x,t,sum)
+            MUSH(3,13,&x,t,sum)
+            MUSH(4,5,&x,t,sum)
+            MUSH(5,7,&x,t,sum)
+            MUSH(6,9,&x,t,sum)
+            MUSH(7,13,&x,t,sum)
+            MUSH(8,5,&x,t,sum)
+            MUSH(9,7,&x,t,sum)
+            MUSH(10,9,&x,t,sum)
+            MUSH(11,13,&x,t,sum)
+        for i in range (8):
+            out[i] ^= t[i+4]
+
+from cython.operator cimport preincrement as incr, predecrement as decr
+
+#cython: cdivision=True
+def dns_random (uint32_t n):
+    "return an unpredictable random number in the range 0-n"
+    global outleft
+    if not n:
+        return 0
+    elif not outleft:
+        if not incr (iin[0]):
+            if not incr (iin[1]):
+                if not incr (iin[2]):
+                    incr(iin[3])
+        surf()
+        outleft = 8
+    return out[decr(outleft)] % n
+
+def set_seed (bytes b):
+    "set the initial seed for the SURF PRNG"
+    cdef int i
+    cdef uint8_t * p
+    p = <uint8_t *> (&seed[0])
+    cdef unsigned char * x = b
+    for i in range (len (b)):
+        p[i] = <uint8_t> x[i]