diff options
Diffstat (limited to 'src/corelib/tools/qsimd.cpp')
-rw-r--r-- | src/corelib/tools/qsimd.cpp | 36 |
1 files changed, 35 insertions, 1 deletions
diff --git a/src/corelib/tools/qsimd.cpp b/src/corelib/tools/qsimd.cpp index fb9b5996f6..6e3b0f9faf 100644 --- a/src/corelib/tools/qsimd.cpp +++ b/src/corelib/tools/qsimd.cpp @@ -626,8 +626,40 @@ void qDumpCPUFeatures() # ifdef Q_PROCESSOR_X86_64 # define _rdrandXX_step _rdrand64_step +# define _rdseedXX_step _rdseed64_step # else # define _rdrandXX_step _rdrand32_step +# define _rdseedXX_step _rdseed32_step +# endif + +# if QT_COMPILER_SUPPORTS_HERE(RDSEED) +static QT_FUNCTION_TARGET(RDSEED) unsigned *qt_random_rdseed(unsigned *ptr, unsigned *end) noexcept +{ + // Unlike for the RDRAND code below, the Intel whitepaper describing the + // use of the RDSEED instruction indicates we should not retry in a loop. + // If the independent bit generator used by RDSEED is out of entropy, it + // may take time to replenish. + // https://software.intel.com/en-us/articles/intel-digital-random-number-generator-drng-software-implementation-guide + while (ptr + sizeof(qregisteruint)/sizeof(*ptr) <= end) { + if (_rdseedXX_step(reinterpret_cast<qregisteruint *>(ptr)) == 0) + goto out; + ptr += sizeof(qregisteruint)/sizeof(*ptr); + } + + if (sizeof(*ptr) != sizeof(qregisteruint) && ptr != end) { + if (_rdseed32_step(ptr) == 0) + goto out; + ++ptr; + } + +out: + return ptr; +} +# else +static unsigned *qt_random_rdseed(unsigned *ptr, unsigned *) +{ + return ptr; +} # endif QT_FUNCTION_TARGET(RDRND) qsizetype qRandomCpu(void *buffer, qsizetype count) noexcept @@ -636,6 +668,9 @@ QT_FUNCTION_TARGET(RDRND) qsizetype qRandomCpu(void *buffer, qsizetype count) no unsigned *end = ptr + count; int retries = 10; + if (qCpuHasFeature(RDSEED)) + ptr = qt_random_rdseed(ptr, end); + while (ptr + sizeof(qregisteruint)/sizeof(*ptr) <= end) { if (_rdrandXX_step(reinterpret_cast<qregisteruint *>(ptr))) ptr += sizeof(qregisteruint)/sizeof(*ptr); @@ -657,5 +692,4 @@ out: } #endif - QT_END_NAMESPACE |