diff options
Diffstat (limited to 'libgcompat/random_r.c')
| -rw-r--r-- | libgcompat/random_r.c | 157 |
1 files changed, 157 insertions, 0 deletions
diff --git a/libgcompat/random_r.c b/libgcompat/random_r.c new file mode 100644 index 0000000..5bc7053 --- /dev/null +++ b/libgcompat/random_r.c @@ -0,0 +1,157 @@ +/* + * ------------------------------------------------------------------- + * Copyright © 2005-2020 Rich Felker, et al. + * + * Permission is hereby granted, free of charge, to any person + * obtaining a copy of this software and associated documentation + * files (the "Software"), to deal in the Software without + * restriction, including without limitation the rights to use, copy, + * modify, merge, publish, distribute, sublicense, and/or sell copies + * of the Software, and to permit persons to whom the Software is + * furnished to do so, subject to the following conditions: + * + * The above copyright notice and this permission notice shall be + * included in all copies or substantial portions of the Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, + * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF + * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND + * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS + * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN + * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN + * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE + * SOFTWARE. + * ------------------------------------------------------------------- + */ + +/* This is an adaptation of musl's random() implementation, adding + * random_data buffers to make reentrant variants + */ + +#include <stddef.h> /* NULL, size_t */ +#include <stdint.h> /* int32_t, uint32_t */ +#include <errno.h> /* errno */ + +/* This code uses the same lagged fibonacci generator as the + * original bsd random implementation except for the seeding + * which was broken in the original + */ + +/* This must use the same struct layout as used by glibc + * and specified in LSB + * ref: https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/libc-ddefs.html + */ +struct random_data { + int32_t *x; /* int32_t *fptr */ + int32_t *unused_1; /* int32_t *rptr */ + int32_t *unused_2; /* int32_t *state */ + int n; /* int rand_type */ + int i; /* int rand_deg */ + int j; /* int rand_sep */ + int32_t *unused_3; /* int32_t *end_ptr */ +}; + +static uint32_t lcg31(uint32_t x) { + return (1103515245*x + 12345) & 0x7fffffff; +} + +static uint64_t lcg64(uint64_t x) { + return 6364136223846793005ull*x + 1; +} + +static void savestate_r(struct random_data *buf) { + buf->x[-1] = (buf->n<<16)|(buf->i<<8)|buf->j; +} + +static void loadstate_r(uint32_t *state, struct random_data *buf) { + buf->x = (int32_t *)state + 1; + buf->n = buf->x[-1]>>16; + buf->i = (buf->x[-1]>>8)&0xff; + buf->j = buf->x[-1]&0xff; +} + +int srandom_r(unsigned seed, struct random_data *buf) { + int k; + uint64_t s = seed; + + if (buf == NULL) { + return -1; + } + + if (buf->n > 63) { + return -1; + } else if (buf->n == 0) { + buf->x[0] = s; + return 0; + } + buf->i = buf->n == 31 || buf->n == 7 ? 3 : 1; + buf->j = 0; + for (k = 0; k < buf->n; k++) { + s = lcg64(s); + buf->x[k] = s>>32; + } + /* make sure x contains at least one odd number */ + buf->x[0] |= 1; + + return 0; +} + +int initstate_r(unsigned seed, char *restrict state, size_t size, + struct random_data *restrict buf) { + if (size < 8) { + errno = EINVAL; + return -1; + } + + savestate_r(buf); + if (size < 32) { + buf->n = 0; + } else if (size < 64) { + buf->n = 7; + } else if (size < 128) { + buf->n = 15; + } else if (size < 256) { + buf->n = 31; + } else { + buf->n = 63; + } + buf->x = (int32_t*)state + 1; + srandom_r(seed, buf); + savestate_r(buf); + return 0; +} + +int setstate_r(char *restrict state, struct random_data *restrict buf) { + if (!state || !buf) { + errno = EINVAL; + return -1; + } + + savestate_r(buf); + loadstate_r((uint32_t*)state, buf); + return 0; +} + +int random_r(struct random_data *restrict buf, int32_t *restrict result) { + long k; + + if (result == NULL || buf == NULL) { + errno = EINVAL; + return -1; + } + + if (buf->n == 0) { + k = buf->x[0] = lcg31(buf->x[0]); + goto end; + } + buf->x[buf->i] += buf->x[buf->j]; + k = buf->x[buf->i]>>1; + if (++(buf->i) == buf->n) { + buf->i = 0; + } if (++(buf->j) == buf->n) { + buf->j = 0; + } +end: + *result = k; + return 0; +} |