2 * The UCW Library -- Random numbers
4 * (c) 2020--2022 Pavel Charvat <pchar@ucw.cz>
6 * This software may be freely distributed and used according to the terms
7 * of the GNU Lesser General Public License.
13 #ifdef CONFIG_UCW_CLEAN_ABI
14 #define fastrand_new ucw_fastrand_new
15 #define fastrand_delete ucw_fastrand_delete
16 #define fastrand_set_seed ucw_fastrand_set_seed
17 #define fastrand_gen_seed_value ucw_fastrand_gen_seed_value
18 #define fastrand_gen_seed ucw_fastrand_gen_seed
19 #define fastrand_has_seed ucw_fastrand_has_seed
20 #define fastrand_reset ucw_fastrand_reset
21 #define fastrand_u32 ucw_fastrand_u32
22 #define fastrand_u64 ucw_fastrand_u64
23 #define fastrand_bits_u64 ucw_fastrand_bits_u64
24 #define fastrand_max ucw_fastrand_max
25 #define fastrand_max_u64 ucw_fastrand_max_u64
26 #define fastrand_mem ucw_fastrand_mem
27 #define fastrand_double ucw_fastrand_double
28 #define strongrand_close ucw_strongrand_close
29 #define strongrand_reset ucw_strongrand_reset
30 #define strongrand_mem ucw_strongrand_mem
31 #define strongrand_std_open ucw_strongrand_std_open
32 #define strongrand_getrandom_mem_try ucw_strongrand_getrandom_mem_try
38 * Context structure for a fast pseudo-random generator.
39 * Useful for generating numbers in randomized algorithms, but not in critical things like cryptography.
40 * The library is generally thread-safe, but each context must be used by at most one thread at one time.
41 * Also be careful with fork() if you want to avoid the same numbers in subprocesses.
46 * Type for a seed value. Beware that some generators are only able to use the lowest 32 bits.
48 typedef u64 fastrand_seed_t;
51 * Allocate a new context. Should be paired with fastrand_delete().
52 * Don't forget to supply a seed before started to read randomness.
54 struct fastrand *fastrand_new(void);
55 void fastrand_delete(struct fastrand *c);
57 /** (Re)seed the context with given value. **/
58 void fastrand_set_seed(struct fastrand *c, fastrand_seed_t seed);
61 * Generate a seed for fastrand_set_seed().
63 * Since glibc 2.25 and kernel 3.17, we use getrandom() syscall
64 * to read kernel's urandom.
66 * Otherwise we mix these things:
68 * -- process id to deal with frequent fork() or startups
69 * -- counter to deal with multiple contexts, for example in threaded application
71 fastrand_seed_t fastrand_gen_seed_value(void);
73 /** (Re)seed the context with fastrand_gen_seed_value(). **/
74 fastrand_seed_t fastrand_gen_seed(struct fastrand *c);
76 /** Is the context seeded? **/
77 bool fastrand_has_seed(struct fastrand *c);
79 /** Reset the context to its initial state. Useful after a fork() to assert forgotten reseed. **/
80 void fastrand_reset(struct fastrand *c);
82 /** Uniformly generate 32 random bits. **/
83 u32 fastrand_u32(struct fastrand *c);
85 /** Uniformly generate 64 random bits. **/
86 u64 fastrand_u64(struct fastrand *c);
88 /** Uniformly generate [0, 64] random bits. **/
89 u64 fastrand_bits_u64(struct fastrand *c, uint bits);
91 /** Uniformly generate [0, 8*sizeof(uint)] random bits. **/
92 static inline uint fastrand_bits(struct fastrand *c, uint bits)
94 return fastrand_bits_u64(c, bits);
97 /** Uniformly generate a random number from range [0, bound-1], where @bound is [1, UINT_MAX]. **/
98 uint fastrand_max(struct fastrand *c, uint bound);
100 /** Uniformly generate a random number from range [0, bound-1], where @bound is [1, UINT64_MAX]. **/
101 u64 fastrand_max_u64(struct fastrand *c, u64 bound);
103 /** Generate @size random bytes. **/
104 void fastrand_mem(struct fastrand *c, void *ptr, size_t size);
106 /** Uniformly generate a random number from range [0.0, 1.0) + possible inaccuracies from basic floating point operations. **/
107 double fastrand_double(struct fastrand *c);
109 /* random-strong.c */
112 * Context structure for a strong random generator.
113 * Useful for things like generating random ids or cryptography.
114 * The library is generally thread-safe, but each context must be used by at most one thread at one time.
116 * Also be careful with fork(). Unless said otherwise, it's forbidden to use the context
117 * in a forked child, we can even assert changes of pid. See strongrand_reset() if you
121 const char *name; /* (mandatory) Context name for logging. */
122 void (*read)(struct strongrand *sr, byte *ptr, int size); /* (mandatory) Generate @size random bytes. */
123 void (*close)(struct strongrand *sr); /* Called from strongrand_close(). */
124 void (*reset)(struct strongrand *sr); /* Called from strongrand_reset(). */
127 /** Close a previously opened context. **/
128 void strongrand_close(struct strongrand *c);
131 * If you want to use the same context in multiple forked subprocesses, you must
132 * call this function after the fork() to flush any buffered randomness.
133 * Some future back-ends could use it for even more things, for example
134 * to re-connect somewhere.
136 void strongrand_reset(struct strongrand *sr);
138 /** Generate @size random bytes. **/
139 void strongrand_mem(struct strongrand *c, void *ptr, size_t size);
142 * Open kernel's random generator.
143 * Requires exactly one of these flags, among others:
144 * -- STRONGRAND_STD_URANDOM
145 * -- STRONGRAND_STD_RANDOM
147 * Since glibc 2.25 and kernel 3.17, we use getrandom() syscall,
148 * otherwise we open and read from "/dev/[u]random" device.
150 * @buf_size can be 0 for unbuffered reading.
152 * STRONGRAND_STD_x_RESET flags are only useful for buffered reading.
154 * If at least one of the following conditions are met, strongrand_reset()
155 * after fork() is not necessary:
157 * -- STRONGRAND_STD_AUTO_RESET flag
158 * -- no read since open or last reset (empty buffer)
160 struct strongrand *strongrand_std_open(uint buf_size, uint flags);
162 enum strongrand_std_flags {
163 STRONGRAND_STD_URANDOM = 0x1, // Use kernel's "urandom" source.
164 STRONGRAND_STD_RANDOM = 0x2, // Use kernel's "random" source.
165 STRONGRAND_STD_DELAYED = 0x4, // Delay non-trivial initializations like opening file descriptor to first read.
166 STRONGRAND_STD_AUTO_RESET = 0x8, // Automatically do strongrand_reset() after changes of getpid(); adds overhead to each read.
167 STRONGRAND_STD_ASSERT_RESET = 0x10, // Assert correct usage of strongrand_reset() after changes of getpid(); for debugging.
171 bool strongrand_getrandom_mem_try(void *buf, size_t size);