pthread locking code - C vs. ASM

[Clemens Kolbitsch]

Hi!
Why are some (e.g. locking) functions implemented twice -- once in C and once 
in assembler? Is the C code used to get an asselber starting point which is 
then optimized and saved into a second file?

For example pthread_rwlock_unlock is implemented in
source/nptl/sysdeps/unix/sysv/linux/i386/i486/pthread_rwlock_unlock.S
and
source/nptl/pthread_rwlock_unlock.c

If I modify the asm code only, is there a chance that some script (e.g. during 
make clean && make) will overwrite my changes or is the ASM code the correct 
place to edit things (otherwise I don't see my modifications being linked 
into the binary...)?

Thanks!