c++ - asm volatile function's output for the provided code -


can explain following function doing:

 inline int atomic_exchange_and_add( int * pw, int dv ) {  int r;   __asm__ __volatile__  (     "lock\n\t"     "xadd %1, %0":     "=m"( *pw ), "=r"( r ): // outputs (%0, %1)     "m"( *pw ), "1"( dv ): // inputs (%2, %3 == %1)     "memory", "cc" // clobbers  ); }

below call:

void weak_release() // nothrow {     if( atomic_exchange_and_add( &weak_count_, -1 ) == 1 )     {         destroy();     } }

thanks in advance


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