hash/log2: Add generic implementations of fls() and fls64()

When importing the hashtable code in I8ef73a62fe9846ce45058eb21cf999dd3eed5741
I didn't import actual implementations of the fls() and fls64()
implementations, as at least gcc-10 was smart enough to detect
we only use it on constant types and hence the computation can happen
at build time via const_ilog2()

However, in our jenkins build verification' this doesn't appear to
happen, as we get below errors:

/build/deps/install/stow/libosmocore/include/osmocom/core/log2.h: In function ‘__ilog2_u32’:
/build/deps/install/stow/libosmocore/include/osmocom/core/log2.h:20:9: error: implicit declaration of function ‘fls’ [-Werror=implicit-function-declaration]
  return fls(n) - 1;
         ^~~
/build/deps/install/stow/libosmocore/include/osmocom/core/log2.h: In function ‘__ilog2_u64’:
/build/deps/install/stow/libosmocore/include/osmocom/core/log2.h:28:9: error: implicit declaration of function ‘fls64’ [-Werror=implicit-function-declaration]
  return fls64(n) - 1;
         ^~~~~

Let's provide some generic implementations for this case.  If needed
one could also introduce architecture-specific assembly implementations
like in the Linux kernel, but so far we managed to keep libosmocore free
of any assembly tweaks.

Change-Id: Ifa4898eb66c8d949618edd47961b7a0330ed35b5

0 files changed, 0 insertions, 0 deletions