From: Masahiro TANAKA <masa16.tanaka@...>
Date: 2011-09-17T19:07:27+09:00
Subject: [ruby-core:39608] Re: [Ruby 1.9 - Bug #4576] Range#step miss the last value, if end-exclusive and has float number

I have not been watching ruby-core, but let me give a comment for this issue.
I proposed Numeric#step algorithm for Float in [ruby-dev:20177],
but that was only for the include_end-case.

> �p (1...6.3).step.to_a # => [1.0, 2.0, 3.0, 4.0, 5.0, 6.0]
> �p (1.1...6).step.to_a # => [1.1, 2.1, 3.1, 4.1, 5.1]
> �p (1...6).step(1.1).to_a # => [1.0, 2.1, 3.2, 4.3, 5.4]
>
> �p (1.0...6.6).step(1.9).to_a # => [1.0, 2.9, 4.0]
> �p (1.0...6.7).step(1.9).to_a # => [1.0, 2.9, 4.8]
> �p (1.0...6.8).step(1.9).to_a # => [1.0, 2.9, 4.8, 6.7]

If this behaviour is expected, a possible algorithm is:

--- numeric.c	(revision 33288)
+++ numeric.c	(working copy)
@@ -1690,8 +1690,16 @@
 	}
 	else {
 	    if (err>0.5) err=0.5;
-	    n = floor(n + err);
-	    if (!excl || ((long)n)*unit+beg < end) n++;
+	    if (excl) {
+		if (n>0) {
+		    if (n<err)
+			n = 1;
+		    else
+			n = floor(n - err) + 1;
+		}
+	    } else {
+		n = floor(n + err) + 1;
+	    }
 	    for (i=0; i<n; i++) {
 		rb_yield(DBL2NUM(i*unit+beg));
 	    }

Masahiro Tanaka