>>422
32ビット整数を32ビット以上シフトした結果は未定義だからです

参考になるサイト
http://www.vmunix.com/~gabor/c/draft.html#101

> If the value of the right operand is negative
> or is greater than or equal to the number of value and sign
> bits in the object representation of the promoted left
> operand, the behavior is undefined.