[Dev-C++] Asmbly language + help

[Smitha V. B. <smi...@so...>]

hi to all..
Does anyone knows what this piece of code means...

#define sys_test_and_set(lock)    \
({                                      \
   volatile long temp = SEMAPHORE_C_SET;  \
   __asm__("xchgl %0,(%2)"              \
           :"=s" (temp)                 \
           :"0" (temp),"r" (lock));     \
   temp;                                \
})


thanking in advance
regards
smitha
*********************************************************************
Disclaimer: The information in this e-mail and any attachments is
confidential / privileged. It is intended solely for the addressee or
addressees. If you are not the addressee indicated in this message, you may
not copy or deliver this message to anyone. In such case, you should destroy
this message and kindly notify the sender by reply email. Please advise
immediately if you or your employer does not consent to Internet email for
messages of this kind.
*********************************************************************