Here are my latest thoughts on what the run-time test for NEON should
probably look like.
Previous proposals used two static variables instead of just one, but
I think that would be less thread-safe.
The variable "cached" is used in only two places, so, provided the
access to it is atomic, the code has a good chance of being
thread-safe even if compiled with -O0. (I don't think "volatile" would
be helpful here.)
#ifdef HAVE_NEON
#ifdef __linux__
#ifdef __aarch64__
/* HWCAP_ASIMD is defined in <asm/hwcap.h> but not included by <sys/auxv.h>.
Since all current AArch64 implementations have NEON/ASIMD it is probably
better to return 1 than include a header file which is not intended for
use by user programs. */
int have_neon(void)
{
return 1;
}
#else
#include <sys/auxv.h>
int have_neon(void)
{
static int cached = 2;
int ret;
/* This should be thread-safe in all reasonable circumstances. */
ret = cached;
if (ret == 2) {
ret = !!(getauxval(AT_HWCAP) & HWCAP_ARM_NEON);
cached = ret;
}
return ret;
}
#endif
#else
#error Please implement a run-time test for NEON/ASIMD for your platform.
#endif
#endif
--
To UNSUBSCRIBE, email to debian-arm-requ...@lists.debian.org
with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
Archive:
https://lists.debian.org/CAHDciUdc3E7NsoYtWrSZpqVRJbSeEE2cExK2=g42bxj8xaj...@mail.gmail.com
