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[Support] Fix sys::GetRandomNumber() to always use a high quality seed. 

llvm-svn: 156414
This commit is contained in:
Daniel Dunbar 2012-05-08 20:38:00 +00:00
parent 5bad4799a3
commit 5f1c956eb0
1 changed files with 15 additions and 5 deletions
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20
llvm/lib/Support/Unix/Process.inc
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@ -12,6 +12,8 @@
//===----------------------------------------------------------------------===//
#include "Unix.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/Support/TimeValue.h"
#ifdef HAVE_SYS_TIME_H
#include <sys/time.h>
#endif
@ -300,13 +302,21 @@ const char *Process::ResetColor() {
#if !defined(HAVE_ARC4RANDOM)
static unsigned GetRandomNumberSeed() {
unsigned seed = ::time(NULL); // FIXME: It might not provide unique seed.
FILE *RandomSource = ::fopen("/dev/urandom", "r");
if (RandomSource) {
::fread((void *)&seed, sizeof(seed), 1, RandomSource);
// Attempt to get the initial seed from /dev/urandom, if possible.
if (FILE *RandomSource = ::fopen("/dev/urandom", "r")) {
unsigned seed;
int count = ::fread((void *)&seed, sizeof(seed), 1, RandomSource);
::fclose(RandomSource);
// Return the seed if the read was successful.
if (count == 1)
return seed;
}
return seed;
// Otherwise, swizzle the current time and the process ID to form a reasonable
// seed.
TimeValue Now = llvm::TimeValue::now();
return hash_combine(Now.seconds(), Now.nanoseconds(), ::getpid());
}
#endif