Some questions about source code

[sunism]

there are two questions about source code:

1. tsz.go

   
   // clamp number of leading zeros to avoid overflow when encoding
       if leading >= 32 {
           leading = 31
       }

the value is float 64 , leading zero is will between 0 and 64, why there use 32?
2. tsz.go

if s.leading != ^uint8(0) && leading >= s.leading && trailing >= s.trailing {

what ahout the meaning of ```s.leading != ^uint8(0)  ``` ??

I really hope to hear from you