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static ngx_inline ngx_atomic_uint_t
ngx_atomic_cmp_set(ngx_atomic_t *lock, ngx_atomic_uint_t old,
ngx_atomic_uint_t set)
{
    u_char res;
    __asm__ volatile (
    NGX_SMP_LOCK
    \" cmpxchgl %3, %1; \"
    \" sete %0; \"
    : \"=a\" (res) : \"m\" (*lock), \"a\" (old), \"r\" (set) : \"cc\", \"memory\");
    return res;
}

printf

 static ngx_inline ngx_atomic_uint_t
 ngx_atomic_cmp_set(ngx_atomic_t *lock, ngx_atomic_uint_t old,
 ngx_atomic_uint_t set)
 {
     u_char res;
     if (*lock == old){
         *lock = set;
         res = 1;
     } else{
         res = *lock
     }
     return res;
  }