[LLVMdev] source code for llvm

[shines_tao]

i don't understand the source code : 
static StringMapEntryBase *getTombstoneVal() {
    return (StringMapEntryBase*)-1;
  }     at "include\llvm\adt\stingmaph"  at line 116. "(StringMapEntryBase*)-1" is it the cast or something other? why there is a * after class StringMapEntryBase?
thank you ~~
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