diff options
Diffstat (limited to 'openbsd-compat/bsd-arc4random.c')
-rw-r--r-- | openbsd-compat/bsd-arc4random.c | 65 |
1 files changed, 65 insertions, 0 deletions
diff --git a/openbsd-compat/bsd-arc4random.c b/openbsd-compat/bsd-arc4random.c index d45fb182a..8bf31e5d3 100644 --- a/openbsd-compat/bsd-arc4random.c +++ b/openbsd-compat/bsd-arc4random.c | |||
@@ -82,3 +82,68 @@ arc4random_stir(void) | |||
82 | rc4_ready = REKEY_BYTES; | 82 | rc4_ready = REKEY_BYTES; |
83 | } | 83 | } |
84 | #endif /* !HAVE_ARC4RANDOM */ | 84 | #endif /* !HAVE_ARC4RANDOM */ |
85 | |||
86 | #ifndef ARC4RANDOM_BUF | ||
87 | void | ||
88 | arc4random_buf(void *_buf, size_t n) | ||
89 | { | ||
90 | size_t i; | ||
91 | u_int32_t r; | ||
92 | char *buf = (char *)_buf; | ||
93 | |||
94 | for (i = 0; i < n; i++) { | ||
95 | if (i % 4 == 0) | ||
96 | r = arc4random(); | ||
97 | buf[i] = r & 0xff; | ||
98 | r >>= 8; | ||
99 | } | ||
100 | i = r = 0; | ||
101 | } | ||
102 | #endif /* !HAVE_ARC4RANDOM_BUF */ | ||
103 | |||
104 | #ifndef ARC4RANDOM_UNIFORM | ||
105 | /* | ||
106 | * Calculate a uniformly distributed random number less than upper_bound | ||
107 | * avoiding "modulo bias". | ||
108 | * | ||
109 | * Uniformity is achieved by generating new random numbers until the one | ||
110 | * returned is outside the range [0, 2**32 % upper_bound). This | ||
111 | * guarantees the selected random number will be inside | ||
112 | * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound) | ||
113 | * after reduction modulo upper_bound. | ||
114 | */ | ||
115 | u_int32_t | ||
116 | arc4random_uniform(u_int32_t upper_bound) | ||
117 | { | ||
118 | u_int32_t r, min; | ||
119 | |||
120 | if (upper_bound < 2) | ||
121 | return 0; | ||
122 | |||
123 | #if (ULONG_MAX > 0xffffffffUL) | ||
124 | min = 0x100000000UL % upper_bound; | ||
125 | #else | ||
126 | /* Calculate (2**32 % upper_bound) avoiding 64-bit math */ | ||
127 | if (upper_bound > 0x80000000) | ||
128 | min = 1 + ~upper_bound; /* 2**32 - upper_bound */ | ||
129 | else { | ||
130 | /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */ | ||
131 | min = ((0xffffffff - (upper_bound << 2)) + 1) % upper_bound; | ||
132 | } | ||
133 | #endif | ||
134 | |||
135 | /* | ||
136 | * This could theoretically loop forever but each retry has | ||
137 | * p > 0.5 (worst case, usually far better) of selecting a | ||
138 | * number inside the range we need, so it should rarely need | ||
139 | * to re-roll. | ||
140 | */ | ||
141 | for (;;) { | ||
142 | r = arc4random(); | ||
143 | if (r >= min) | ||
144 | break; | ||
145 | } | ||
146 | |||
147 | return r % upper_bound; | ||
148 | } | ||
149 | #endif /* !HAVE_ARC4RANDOM_UNIFORM */ | ||