title: perturb byte in _int_malloc( ) in glibc
body: <p>after going through glibc code for <code>malloc()</code> and the actual allocator 
  i.e <code>_int_malloc()</code> function I am not able to figure out the significance of "perturn_byte". Its being used in <code>alloc_perturb macro()</code> at many places in <code>_int_malloc()</code>.</p>
  
  <p>i know this this question is just to specific to answer, please pardon me. But in case anybody already knows the anwser will save me some head banging.</p>
  
  <p>thanks</p>