How many times should I need to perform regression testing (In Manual and Automated)?

When software comes with fix for particular issue, How many times should I need to repeat regression testing? Please answer for both Automated and Manual testing?

Based on which factors, repeating test goes? For example:

1. It is blocker issue. so that we need to run it for 100 times. But again here why do we need or how to set 100 times.
2. It is legal issue. so that I should run for 1000 times.