Minor changes to euclidean algorithm implementation in Common Lisp

[Trashtalk217]

The euclidean algorithm was the first algorithm I ever implemented in Common Lisp and it is due for a revision. I added docstrings and did some changes to imdentation. I also did some research into turning the two functions for euclid-sub and turning it into one single function. I decided against it since alternative implementations were slower.

That's about it, some very small changes to make the code slightly better.

[dovisutu]

I don't know much about Common Lisp, but I find 2 small mistakes in .md file.

[Trashtalk217]

There is a weird thing, where the indentation in the euclid-sub* doesn't work. (euclid-sub* (- a b) b) and (euclid-sub* a (- b a)) line up with (if instead of (> a b). It looks fine in my editor, but when serverd it's wrong.

Could someone try to build it on their own machine and check how it looks?

EDIT: I think the .md problems from @dovisutu are fixed.

[Trashtalk217]

Fixed it. This is PR is good to go in my eyes. A review is still needed and appreciated though.

[berquist]

The rename confused Git, so here is the actual diff:

diff --git a/euclidean_algorithm.lisp b/temp.lisp
index cff5ab2..3b8dcad 100644
--- a/euclidean_algorithm.lisp
+++ b/temp.lisp
@@ -1,33 +1,32 @@
-;;;; Euclid algorithm implementation
+;;;; Euclidean algorithm implementation in Common Lisp

 (defun euclid-sub (a b)
+  "Finds the greatest common divsor for any two integers"
   (euclid-sub* (abs a) (abs b)))

 (defun euclid-sub* (a b)
+  "Finds the greatest common divisor for any two positive integers"
   (if (eq a b)
-    a
-    (if (> a b)
-      (euclid-sub* (- a b) b)
-      (euclid-sub* a (- b a)))))
+      a
+      (if (> a b)
+             (euclid-sub* (- a b) b)
+             (euclid-sub* a (- b a)))))

 (defun euclid-mod (a b)
+  "Finds the greatest common divisor for any two integers"
   (if (zerop b)
-    (abs a)
-    (euclid-mod b (mod a b))))
+      (abs a)
+      (euclid-mod b (mod a b))))

-(print
-  (euclid-sub (* 64 67)
-              (* 64 81)))
-(print
-  (euclid-mod (* 128 12)
-              (* 128 77)))
+(print (euclid-sub (* 64 67) (* 64 81)))
+(print (euclid-mod (* 128 12) (* 128 77)))

-;; built-in function: (gcd 80 40)
-;; quick test
-(assert
-  (=  (euclid-sub (* 64 67) (* 64 81))
-      (gcd (* 64 67) (* 64 81))))
+;; Quick test
+(assert
+ (eql  (euclid-sub (* 64 67) (* 64 81))
+       (gcd (* 64 67) (* 64 81))))

-(assert
-  (=  (euclid-mod (* 64 67) (* 64 81))
+(assert
+ (eql (euclid-mod (* 64 67) (* 64 81))
       (gcd (* 64 67) (* 64 81))))
+

[berquist]

Everything still functionally works, so that's good. I also approve of the change from = to eql according to https://stackoverflow.com/a/548774. Just a few nits left.

(I have noticed that out of the box, Emacs does not indent CL like this, so I'll provide some instructions on the wiki for those of us who use it on changing that.)

[berquist]

Looks good. The breakage is due to some transitive dependencies having nothing to do with your code (see #620 (comment)). I'll wait to merge until we know more about that.

[berquist]

@Trashtalk217 Something I commented on indirectly: the file rename made it hard to compare changes (see #609 (comment)). If you're going to do a file rename, in order for Git to not get confused, it's best to either

1. In one or more commits, make all your changes, and then finally make one commit where you rename the file, or
2. rename the file before making any changes, commit, and then make your change commits.

This way you can force git diff to actually show the changes, rather than the temp file hack I needed here.