git.squeep.com Git - reservoir_sample/blob - randomness.c

   1 #include <stdlib.h>
   2 #include <unistd.h>
   3 #include <fcntl.h>
   4 #include <string.h>
   5 #include <time.h>
   6 #include <errno.h>
   7 #include <assert.h>
   8
   9 #include "randomness.h"
  10 #include "notify.h"
  11
  12 static int randomness_fd_ = -1;
  13
  14 int randomness_init(const char *filename) {
  15         if (filename != NULL) {
  16                 randomness_fd_ = open(filename, O_RDONLY);
  17                 if (randomness_fd_ == -1) {
  18                         NOTIFY_ERROR("%s('%s'):%s", "open", filename, strerror(errno));
  19                         return -1;
  20                 }
  21                 NOTIFY_DEBUG("reading randomness from '%s', fd:%d", filename, randomness_fd_);
  22         } else {
  23                 if (randomness_fd_ != -1) {
  24                         close(randomness_fd_);
  25                         randomness_fd_ = -1;
  26                 }
  27                 srand48(time(NULL) ^ getpid());
  28                 NOTIFY_DEBUG("reading randomness from system PRNG");
  29         }
  30
  31         return 0;
  32 }
  33
  34 /*
  35         Room for improvement: constrain bits of randomness consumed, based on #limit
  36         Also maybe read chunks of randomness at a time
  37  */
  38 unsigned long randomness_upto_inclusive(unsigned long limit) {
  39         unsigned long randomness;
  40
  41         if (limit == 0)
  42                 return 0;
  43
  44         if (randomness_fd_ != -1) {
  45                 ssize_t len;
  46
  47                 do {
  48                         len = read(randomness_fd_, &randomness, sizeof randomness);
  49                 } while (len == -1 && (errno == EINTR || errno == EAGAIN));
  50                 if (len == sizeof randomness) {
  51                         randomness %= limit + 1;
  52                         NOTIFY_DEBUG("randomness:%lu", randomness);
  53                         return randomness;
  54                 }
  55                 NOTIFY_ERROR("%s(%d, %zu):%zd:%s",
  56                              "read", randomness_fd_, sizeof randomness, len,
  57                              (len < 0) ? strerror(errno) : ( (len == 0) ? "EOF" : "not enough read" )
  58                             );
  59         }
  60
  61         /* fall back to pseudo-randomness if read failed */
  62         randomness = mrand48();
  63         randomness %= limit + 1;
  64
  65         NOTIFY_DEBUG("randomness:%lu", randomness);
  66         return randomness;
  67 }