Add CPU_FLAG_NONE that's first in the list and represents a CPU without
any acceleration features. Can be used for reference/fallback
implementation.
Signed-off-by: David Sterba <dsterba@suse.com>
Add support for run-time detection of CPU features on x86_64 to allow
selection of accelerated implementations of hash algorithms.
When possible use the compiler builtin (works on gcc and clang).
The SHA extensions can't be detected by __builtin_cpu_supports and the
__cpuid/__cpuidex macros are not consistently provided in all supported
gcc and clang versions. Copy the __cpuidex and call it manually for the
SHA extensions. Complete list https://en.wikipedia.org/wiki/CPUID .
Signed-off-by: David Sterba <dsterba@suse.com>
