A specific implementation of an algorithm is already protected by copyright. Copyright also protects "minor" alterations to your work, and derivative works. That answers most of your questions.
The problem is that algorithms are abstract, and patents are intended to apply to concrete solutions. That is why the original case that opened the door said that the use of software did not prevent a concrete solution from being patentable. This has been twisted since to say that software itself can be patented. An analogy in copyright would be "copyrighting" all stories about boy wizards, as opposed to a concrete expression of such a story.
A concrete piece of software is protected by copyright. Every software "patent" granted is abstract and kills entire categories of creative expression. In fact, it now kills *all* creative expression. At this point, every line of code any of us writes violates some software "patent". It is just a matter of when some troll gets around to suing us, or whether we have any counter patents in our arsenal that the plaintiff is also violating (should the suing company have an actual product - hey, at least Oracle isn't a troll).
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Patent != copyright. In general, free software advocates are in favor of copyright, but not patents for software.
A specific implementation of an algorithm is already protected by copyright. Copyright also protects "minor" alterations to your work, and derivative works. That answers most of your questions.
The problem is that algorithms are abstract, and patents are intended to apply to concrete solutions. That is why the original case that opened the door said that the use of software did not prevent a concrete solution from being patentable. This has been twisted since to say that software itself can be patented. An analogy in copyright would be "copyrighting" all stories about boy wizards, as opposed to a concrete expression of such a story.
A concrete piece of software is protected by copyright. Every software "patent" granted is abstract and kills entire categories of creative expression. In fact, it now kills *all* creative expression. At this point, every line of code any of us writes violates some software "patent". It is just a matter of when some troll gets around to suing us, or whether we have any counter patents in our arsenal that the plaintiff is also violating (should the suing company have an actual product - hey, at least Oracle isn't a troll).