1 /* 2 * Copyright (C) 2003 Sean Chittenden <seanc@FreeBSD.org> 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND 15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17 * ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE 18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24 * SUCH DAMAGE. 25 */ 26 27 #ifndef __RANDOMIZE_FD__ 28 #define __RANDOMIZE_FD__ 29 30 #define RANDOM_TYPE_UNSET 0 31 #define RANDOM_TYPE_LINES 1 32 #define RANDOM_TYPE_WORDS 2 33 34 /* The multiple instance single integer key */ 35 struct rand_node { 36 u_char *cp; 37 u_int len; 38 struct rand_node *next; 39 }; 40 41 int randomize_fd(int fd, int type, int unique, double denom); 42 43 /* 44 * Generates a random number uniformly in the range [0.0, 1.0). 45 */ 46 static inline double 47 random_unit_float(void) 48 { 49 static const uint64_t denom = (1ull << 53); 50 static const uint64_t mask = denom - 1; 51 52 uint64_t rand64; 53 54 /* 55 * arc4random_buf(...) in this use generates integer outputs in [0, 56 * UINT64_MAX]. 57 * 58 * The double mantissa only has 53 bits, so we uniformly mask off the 59 * high 11 bits and then floating-point divide by 2^53 to achieve a 60 * result in [0, 1). 61 * 62 * We are not allowed to emit 1.0, so denom must be one greater than 63 * the possible range of the preceeding step. 64 */ 65 arc4random_buf(&rand64, sizeof(rand64)); 66 rand64 &= mask; 67 return ((double)rand64 / denom); 68 } 69 70 /* 71 * Returns true with probability 1 / denom (a floating point number >= 1). 72 * Otherwise, returns false. 73 */ 74 static inline bool 75 random_uniform_denom(double denom) 76 { 77 return ((uint64_t)(denom * random_unit_float()) == 0); 78 } 79 #endif 80