# include <stdlib.h>
#endif
-#if defined USE_RDRAND || defined USE_RDSEED \
- || defined _GLIBCXX_USE_CRT_RAND_S || defined _GLIBCXX_USE_DEV_RANDOM
+#if defined _GLIBCXX_USE_CRT_RAND_S || defined _GLIBCXX_USE_DEV_RANDOM
+// The OS provides a source of randomness we can use.
# pragma GCC poison _M_mt
+#elif defined USE_RDRAND || defined USE_RDSEED
+// Hardware instructions might be available, but use cpuid checks at runtime.
+# pragma GCC poison _M_mt
+// If the runtime cpuid checks fail we'll use a linear congruential engine.
+# define USE_LCG 1
#else
// Use the mt19937 member of the union, as in previous GCC releases.
# define USE_MT19937 1
#endif
+#ifdef USE_LCG
+# include <chrono>
+#endif
+
namespace std _GLIBCXX_VISIBILITY(default)
{
namespace
return val;
}
#endif
+
+#ifdef USE_LCG
+ // TODO: use this to seed std::mt19937 engine too.
+ unsigned
+ bad_seed(void* p) noexcept
+ {
+ // Poor quality seed based on hash of the current time and the address
+ // of the object being seeded. Better than using the same default seed
+ // for every object though.
+ const uint64_t bits[] = {
+ (uint64_t) chrono::system_clock::now().time_since_epoch().count(),
+ (uint64_t) reinterpret_cast<uintptr_t>(p)
+ };
+ auto bytes = reinterpret_cast<const unsigned char*>(bits);
+ // 32-bit FNV-1a hash
+ uint32_t h = 2166136261u;
+ for (unsigned i = 0; i < sizeof(bits); ++i)
+ {
+ h ^= *bytes++;
+ h *= 16777619u;
+ }
+ return h;
+ }
+
+ // Same as std::minstd_rand0 but using unsigned not uint_fast32_t.
+ using lcg_type
+ = linear_congruential_engine<unsigned, 16807UL, 0UL, 2147483647UL>;
+
+ inline lcg_type*
+ construct_lcg_at(void* addr) noexcept
+ {
+ return ::new(addr) lcg_type(bad_seed(addr));
+ }
+
+ inline void
+ destroy_lcg_at(void* addr) noexcept
+ {
+ static_cast<lcg_type*>(addr)->~lcg_type();
+ }
+
+ unsigned int
+ __lcg(void* ptr) noexcept
+ {
+ auto& lcg = *static_cast<lcg_type*>(ptr);
+ return lcg();
+ }
+#endif
}
void
_M_fd = -1;
const char* fname [[gnu::unused]] = nullptr;
- bool default_token [[gnu::unused]] = false;
- enum { rand_s, rdseed, rdrand, device_file } which;
+ enum {
+ rand_s = 1, rdseed = 2, rdrand = 4, device_file = 8, prng = 16,
+ any = 0xffff
+ } which;
if (token == "default")
{
- default_token = true;
+ which = any;
fname = "/dev/urandom";
-#if defined _GLIBCXX_USE_CRT_RAND_S
- which = rand_s;
-#elif defined USE_RDSEED
- which = rdseed;
-#elif defined USE_RDRAND
- which = rdrand;
-#elif defined _GLIBCXX_USE_DEV_RANDOM
- which = device_file;
-#else
-# error "either define USE_MT19937 above or set the default device here"
-#endif
}
#ifdef USE_RDSEED
else if (token == "rdseed")
which = device_file;
}
#endif // _GLIBCXX_USE_DEV_RANDOM
+#ifdef USE_LCG
+ else if (token == "prng")
+ which = prng;
+#endif
else
std::__throw_runtime_error(
__N("random_device::random_device(const std::string&):"
" unsupported token"));
- switch (which)
- {
#ifdef _GLIBCXX_USE_CRT_RAND_S
- case rand_s:
- {
- _M_func = &__winxp_rand_s;
- return;
- }
+ if (which & rand_s)
+ {
+ _M_func = &__winxp_rand_s;
+ return;
+ }
#endif // _GLIBCXX_USE_CRT_RAND_S
+
#ifdef USE_RDSEED
- case rdseed:
- {
- unsigned int eax, ebx, ecx, edx;
- // Check availability of cpuid and, for now at least, also the
- // CPU signature for Intel and AMD.
- if (__get_cpuid_max(0, &ebx) > 0
- && (ebx == signature_INTEL_ebx || ebx == signature_AMD_ebx))
- {
- // CPUID.(EAX=07H, ECX=0H):EBX.RDSEED[bit 18]
- __cpuid_count(7, 0, eax, ebx, ecx, edx);
- if (ebx & bit_RDSEED)
- {
+ if (which & rdseed)
+ {
+ unsigned int eax, ebx, ecx, edx;
+ // Check availability of cpuid and, for now at least, also the
+ // CPU signature for Intel and AMD.
+ if (__get_cpuid_max(0, &ebx) > 0
+ && (ebx == signature_INTEL_ebx || ebx == signature_AMD_ebx))
+ {
+ // CPUID.(EAX=07H, ECX=0H):EBX.RDSEED[bit 18]
+ __cpuid_count(7, 0, eax, ebx, ecx, edx);
+ if (ebx & bit_RDSEED)
+ {
#ifdef USE_RDRAND
- // CPUID.01H:ECX.RDRAND[bit 30]
- __cpuid(1, eax, ebx, ecx, edx);
- if (ecx & bit_RDRND)
- {
- _M_func = &__x86_rdseed_rdrand;
- return;
- }
+ // CPUID.01H:ECX.RDRAND[bit 30]
+ __cpuid(1, eax, ebx, ecx, edx);
+ if (ecx & bit_RDRND)
+ {
+ _M_func = &__x86_rdseed_rdrand;
+ return;
+ }
#endif
- _M_func = &__x86_rdseed;
- return;
- }
- }
- // If rdseed was explicitly requested then we're done here.
- if (!default_token)
- break;
- // Otherwise fall through to try the next available option.
- [[gnu::fallthrough]];
- }
+ _M_func = &__x86_rdseed;
+ return;
+ }
+ }
+ }
#endif // USE_RDSEED
+
#ifdef USE_RDRAND
- case rdrand:
- {
- unsigned int eax, ebx, ecx, edx;
- // Check availability of cpuid and, for now at least, also the
- // CPU signature for Intel and AMD.
- if (__get_cpuid_max(0, &ebx) > 0
- && (ebx == signature_INTEL_ebx || ebx == signature_AMD_ebx))
- {
- // CPUID.01H:ECX.RDRAND[bit 30]
- __cpuid(1, eax, ebx, ecx, edx);
- if (ecx & bit_RDRND)
- {
- _M_func = &__x86_rdrand;
- return;
- }
- }
- // If rdrand was explicitly requested then we're done here.
- if (!default_token)
- break;
- // Otherwise fall through to try the next available option.
- [[gnu::fallthrough]];
- }
+ if (which & rdrand)
+ {
+ unsigned int eax, ebx, ecx, edx;
+ // Check availability of cpuid and, for now at least, also the
+ // CPU signature for Intel and AMD.
+ if (__get_cpuid_max(0, &ebx) > 0
+ && (ebx == signature_INTEL_ebx || ebx == signature_AMD_ebx))
+ {
+ // CPUID.01H:ECX.RDRAND[bit 30]
+ __cpuid(1, eax, ebx, ecx, edx);
+ if (ecx & bit_RDRND)
+ {
+ _M_func = &__x86_rdrand;
+ return;
+ }
+ }
+ }
#endif // USE_RDRAND
+
#ifdef _GLIBCXX_USE_DEV_RANDOM
- case device_file:
- {
+ if (which & device_file)
+ {
#ifdef USE_POSIX_FILE_IO
- _M_fd = ::open(fname, O_RDONLY);
- if (_M_fd != -1)
- {
- // Set _M_file to non-null so that _M_fini() will do clean up.
- _M_file = &_M_fd;
- return;
- }
-#else // USE_POSIX_FILE_IO
- _M_file = static_cast<void*>(std::fopen(fname, "rb"));
- if (_M_file)
+ _M_fd = ::open(fname, O_RDONLY);
+ if (_M_fd != -1)
+ {
+ // Set _M_file to non-null so that _M_fini() will do clean up.
+ _M_file = &_M_fd;
return;
+ }
+#else // USE_POSIX_FILE_IO
+ _M_file = static_cast<void*>(std::fopen(fname, "rb"));
+ if (_M_file)
+ return;
#endif // USE_POSIX_FILE_IO
- [[gnu::fallthrough]];
- }
+ }
#endif // _GLIBCXX_USE_DEV_RANDOM
- default:
- { }
+
+#ifdef USE_LCG
+ // Either "prng" was requested explicitly, or "default" was requested
+ // but nothing above worked, use a PRNG.
+ if (which & prng)
+ {
+ static_assert(sizeof(lcg_type) <= sizeof(_M_fd), "");
+ static_assert(alignof(lcg_type) <= alignof(_M_fd), "");
+ _M_file = construct_lcg_at(&_M_fd);
+ _M_func = &__lcg;
+ return;
}
+#endif
+
std::__throw_runtime_error(
__N("random_device::random_device(const std::string&):"
" device not available"));
{
#ifdef USE_MT19937
unsigned long seed = 5489UL;
- if (token != "default" && token != "mt19937")
+ if (token != "default" && token != "mt19937" && token != "prng")
{
const char* nptr = token.c_str();
char* endptr;
if (!_M_file)
return;
+#if USE_LCG
+ if (_M_func == &__lcg)
+ {
+ destroy_lcg_at(_M_file);
+ return;
+ }
+#endif
+
#ifdef USE_POSIX_FILE_IO
::close(_M_fd);
_M_fd = -1;
return _M_mt();
#else
-#if defined USE_RDRAND || defined USE_RDSEED || defined _GLIBCXX_USE_CRT_RAND_S
if (_M_func)
- return _M_func(nullptr);
-#endif
+ return _M_func(_M_file);
result_type ret;
void* p = &ret;
0x9d2c5680UL, 15,
0xefc60000UL, 18, 1812433253UL>;
#endif // USE_MT19937
+
+#ifdef USE_LCG
+ template class
+ linear_congruential_engine<unsigned, 16807UL, 0UL, 2147483647UL>;
+ template struct __detail::_Mod<unsigned, 2147483647UL, 16807UL, 0UL>;
+#endif
}
#endif // _GLIBCXX_USE_C99_STDINT_TR1
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