add file for the isaac64 random number generator

This is the version from the Comprehensive C Archive Network, licensed
under the CC0 "No Rights Reserved" Creative Common License.
http://ccodearchive.net/info/isaac.html

include/isaac64.h

@@ -0,0 +1,131 @@
+/* CC0 (Public domain) - see LICENSE file for details */
+#if !defined(_isaac64_H)
+# define _isaac64_H (1)
+# include <stdint.h>
+
+
+
+typedef struct isaac64_ctx isaac64_ctx;
+
+
+
+#define ISAAC64_SZ_LOG      (8)
+#define ISAAC64_SZ          (1<<ISAAC64_SZ_LOG)
+#define ISAAC64_SEED_SZ_MAX (ISAAC64_SZ<<3)
+
+
+
+/*ISAAC is the most advanced of a series of pseudo-random number generators
+   designed by Robert J. Jenkins Jr. in 1996.
+  http://www.burtleburtle.net/bob/rand/isaac.html
+  This is the 64-bit version.
+  To quote:
+    ISAAC-64 generates a different sequence than ISAAC, but it uses the same
+     principles.
+    It uses 64-bit arithmetic.
+    It generates a 64-bit result every 19 instructions.
+    All cycles are at least 2**72 values, and the average cycle length is
+     2**16583.*/
+struct isaac64_ctx{
+  unsigned n;
+  uint64_t r[ISAAC64_SZ];
+  uint64_t m[ISAAC64_SZ];
+  uint64_t a;
+  uint64_t b;
+  uint64_t c;
+};
+
+
+/**
+ * isaac64_init - Initialize an instance of the ISAAC64 random number generator.
+ * @_ctx:   The ISAAC64 instance to initialize.
+ * @_seed:  The specified seed bytes.
+ *          This may be NULL if _nseed is less than or equal to zero.
+ * @_nseed: The number of bytes to use for the seed.
+ *          If this is greater than ISAAC64_SEED_SZ_MAX, the extra bytes are
+ *           ignored.
+ */
+void isaac64_init(isaac64_ctx *_ctx,const unsigned char *_seed,int _nseed);
+
+/**
+ * isaac64_reseed - Mix a new batch of entropy into the current state.
+ * To reset ISAAC64 to a known state, call isaac64_init() again instead.
+ * @_ctx:   The instance to reseed.
+ * @_seed:  The specified seed bytes.
+ *          This may be NULL if _nseed is zero.
+ * @_nseed: The number of bytes to use for the seed.
+ *          If this is greater than ISAAC64_SEED_SZ_MAX, the extra bytes are
+ *           ignored.
+ */
+void isaac64_reseed(isaac64_ctx *_ctx,const unsigned char *_seed,int _nseed);
+/**
+ * isaac64_next_uint64 - Return the next random 64-bit value.
+ * @_ctx: The ISAAC64 instance to generate the value with.
+ */
+uint64_t isaac64_next_uint64(isaac64_ctx *_ctx);
+/**
+ * isaac64_next_uint - Uniform random integer less than the given value.
+ * @_ctx: The ISAAC64 instance to generate the value with.
+ * @_n:   The upper bound on the range of numbers returned (not inclusive).
+ *        This must be greater than zero and less than 2**64.
+ *        To return integers in the full range 0...2**64-1, use
+ *         isaac64_next_uint64() instead.
+ * Return: An integer uniformly distributed between 0 and _n-1 (inclusive).
+ */
+uint64_t isaac64_next_uint(isaac64_ctx *_ctx,uint64_t _n);
+/**
+ * isaac64_next_float - Uniform random float in the range [0,1).
+ * @_ctx: The ISAAC64 instance to generate the value with.
+ * Returns a high-quality float uniformly distributed between 0 (inclusive)
+ *  and 1 (exclusive).
+ * All of the float's mantissa bits are random, e.g., the least significant bit
+ *  may still be non-zero even if the value is less than 0.5, and any
+ *  representable float in the range [0,1) has a chance to be returned, though
+ *  values very close to zero become increasingly unlikely.
+ * To generate cheaper float values that do not have these properties, use
+ *   ldexpf((float)isaac64_next_uint64(_ctx),-64);
+ */
+float isaac64_next_float(isaac64_ctx *_ctx);
+/**
+ * isaac64_next_signed_float - Uniform random float in the range (-1,1).
+ * @_ctx: The ISAAC64 instance to generate the value with.
+ * Returns a high-quality float uniformly distributed between -1 and 1
+ *  (exclusive).
+ * All of the float's mantissa bits are random, e.g., the least significant bit
+ *  may still be non-zero even if the magnitude is less than 0.5, and any
+ *  representable float in the range (-1,1) has a chance to be returned, though
+ *  values very close to zero become increasingly unlikely.
+ * To generate cheaper float values that do not have these properties, use
+ *   ldexpf((float)isaac64_next_uint64(_ctx),-63)-1;
+ *  though this returns values in the range [-1,1).
+ */
+float isaac64_next_signed_float(isaac64_ctx *_ctx);
+/**
+ * isaac64_next_double - Uniform random double in the range [0,1).
+ * @_ctx: The ISAAC64 instance to generate the value with.
+ * Returns a high-quality double uniformly distributed between 0 (inclusive)
+ *  and 1 (exclusive).
+ * All of the double's mantissa bits are random, e.g., the least significant
+ *  bit may still be non-zero even if the value is less than 0.5, and any
+ *  representable double in the range [0,1) has a chance to be returned, though
+ *  values very close to zero become increasingly unlikely.
+ * To generate cheaper double values that do not have these properties, use
+ *   ldexp((double)isaac64_next_uint64(_ctx),-64);
+ */
+double isaac64_next_double(isaac64_ctx *_ctx);
+/**
+ * isaac64_next_signed_double - Uniform random double in the range (-1,1).
+ * @_ctx: The ISAAC64 instance to generate the value with.
+ * Returns a high-quality double uniformly distributed between -1 and 1
+ *  (exclusive).
+ * All of the double's mantissa bits are random, e.g., the least significant
+ *  bit may still be non-zero even if the value is less than 0.5, and any
+ *  representable double in the range (-1,1) has a chance to be returned,
+ *  though values very close to zero become increasingly unlikely.
+ * To generate cheaper double values that do not have these properties, use
+ *   ldexp((double)isaac64_next_uint64(_ctx),-63)-1;
+ *  though this returns values in the range [-1,1).
+ */
+double isaac64_next_signed_double(isaac64_ctx *_ctx);
+
+#endif