Add static inline function to align a value to it's next power of 2.
This is commonly done by a SWAR like the one in:
http://aggregate.org/MAGIC/#Next Largest Power of 2
However a microbench shows that the implementation herer is a faster.
It doesn't really impact the possible user of this function, but it's
interesting nonetheless.
Using a x86_64 i7 Ivy Bridge it shows a ~4% advantage by using clz
instead instead of the OR and SHL chain. And this is by using a BSR
since Ivy Bridge doesn't have LZCNT. New Haswell processors have the
LZCNT instruction which can make this even better. ARM also has a CLZ
instruction so it should be better, too.
Code used to test:
...
v = val[i];
t1 = get_cycles(0);
a = ALIGN_POWER2(v);
t1 = get_cycles(t1);
t2 = get_cycles(0);
v = nlpo2(v);
t2 = get_cycles(t2);
printf("%u\t%llu\t%llu\t%d\n", v, t1, t2, v == a);
...
In which val is an array of 20 random unsigned int, nlop2 is the SWAR
implementation and get_cycles uses RDTSC to measure the performance.
Averages:
ALIGN_POWER2: 30 cycles
nlop2: 31.4 cycles
Fix compilation issue with musl-libc:
CC libkmod/libkmod-list.lo
In file included from libkmod/libkmod-private.h:183:0,
from libkmod/libkmod-list.c:24:
libkmod/libkmod-util.h:33:45: warning: 'struct stat' declared inside parameter list [enabled by default]
libkmod/libkmod-util.h:33:45: warning: its scope is only this definition or declaration, which is probably not what you want [enabled by default]
Only the public header maintains #ifndef in the header, together with
pragma. The other ones contain only pragma.
As reported by Shawn Landden on systemd mailing list this is compatible
with all major compilers and gcc has this since version 3.3.
If we don't have --gc-sections support, linking kmod fails:
libkmod/.libs/libkmod-util.a(libkmod-util.o): In function 'underscores':
libkmod/libkmod-util.c:117: undefined reference to 'kmod_log'
This is because libkmod-util.la uses kmod_log(), that is in libkmod.la.
Move the function so we don't have a dependency loop while building the
libraries and it works with compilers with no support for --gc-sections.
Not all libc's have a mtim member in struct stat (dietlibc doesn't).
Change ts_usec() to receive a struct stat as parameter and implement it
accordingly for both cases.
Module aliases can be bigger than NAME_MAX. So, replace with PATH_MAX
that is bigger enough to hold them.
Technically in some places NAME_MAX would be sufficient (those using
module names only), but they use functions that can be called with
alias. So increase the buffers in these cases to PATH_MAX too.
