libc neutral random function derived from a drand48() implementation added. Will...

[redis.git] / src / rand.c

diff --git a/src/rand.c b/src/rand.c
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+/* Pseudo random number generation functions derived from the drand48()
+ * function obtained from pysam source code.
+ *
+ * This functions are used in order to replace the default math.random()
+ * Lua implementation with something having exactly the same behavior
+ * across different systems (by default Lua uses libc's rand() that is not
+ * required to implement a specific PRNG generating the same sequence
+ * in different systems if seeded with the same integer).
+ *
+ * The original code appears to be under the public domain.
+ * I modified it removing the non needed functions and all the
+ * 1960-style C coding stuff...
+ *
+ * ----------------------------------------------------------------------------
+ *
+ * Copyright (c) 2011, Salvatore Sanfilippo <antirez at gmail dot com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   * Redistributions of source code must retain the above copyright notice,
+ *     this list of conditions and the following disclaimer.
+ *   * Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *   * Neither the name of Redis nor the names of its contributors may be used
+ *     to endorse or promote products derived from this software without
+ *     specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <stdint.h>
+
+#define N      16
+#define MASK   ((1 << (N - 1)) + (1 << (N - 1)) - 1)
+#define LOW(x) ((unsigned)(x) & MASK)
+#define HIGH(x)        LOW((x) >> N)
+#define MUL(x, y, z)   { int32_t l = (long)(x) * (long)(y); \
+               (z)[0] = LOW(l); (z)[1] = HIGH(l); }
+#define CARRY(x, y)    ((int32_t)(x) + (long)(y) > MASK)
+#define ADDEQU(x, y, z)        (z = CARRY(x, (y)), x = LOW(x + (y)))
+#define X0     0x330E
+#define X1     0xABCD
+#define X2     0x1234
+#define A0     0xE66D
+#define A1     0xDEEC
+#define A2     0x5
+#define C      0xB
+#define SET3(x, x0, x1, x2)    ((x)[0] = (x0), (x)[1] = (x1), (x)[2] = (x2))
+#define SETLOW(x, y, n) SET3(x, LOW((y)[n]), LOW((y)[(n)+1]), LOW((y)[(n)+2]))
+#define SEED(x0, x1, x2) (SET3(x, x0, x1, x2), SET3(a, A0, A1, A2), c = C)
+#define REST(v)        for (i = 0; i < 3; i++) { xsubi[i] = x[i]; x[i] = temp[i]; } \
+               return (v);
+#define HI_BIT (1L << (2 * N - 1))
+
+static uint32_t x[3] = { X0, X1, X2 }, a[3] = { A0, A1, A2 }, c = C;
+static void next();
+
+int32_t redisLrand48() {
+    next();
+    return (((int32_t)x[2] << (N - 1)) + (x[1] >> 1));
+}
+
+void redisSrand48(int32_t seedval) {
+    SEED(X0, LOW(seedval), HIGH(seedval));
+}
+
+static void next() {
+    uint32_t p[2], q[2], r[2], carry0, carry1;
+
+    MUL(a[0], x[0], p);
+    ADDEQU(p[0], c, carry0);
+    ADDEQU(p[1], carry0, carry1);
+    MUL(a[0], x[1], q);
+    ADDEQU(p[1], q[0], carry0);
+    MUL(a[1], x[0], r);
+    x[2] = LOW(carry0 + carry1 + CARRY(p[1], r[0]) + q[1] + r[1] +
+            a[0] * x[2] + a[1] * x[1] + a[2] * x[0]);
+    x[1] = LOW(p[1] + r[0]);
+    x[0] = LOW(p[0]);
+}