Days between 2 unix epoch

#!/bin/bash
# Calculate "days diff" (unix epoch)
function daysdiff {
    begin=${1:-0}
    end=${2:-0}
    let Sec=$end-$begin

    if ((Sec < 0)); then
      echo $((Sec/-86400))
    else
      echo $((Sec/86400));
    fi
    return 0
}