From: nobu.nokada@...
Date: 2004-04-22T13:40:43+09:00
Subject: Re: 5.000...007.to_s => "5"

Hi,

At Thu, 22 Apr 2004 11:33:44 +0900,
Jeff Mitchell wrote in [ruby-talk:97988]:
> Oddly enough, with your patch the first two floats are fixed,
> showing 24.0 and 28.0 (which is entirely a coincidence; this
> list didn't exist when I came up with the original numbers).
> The rest are as shown.

$ cat f.rb
#! /usr/bin/ruby
require 'hexfloat'	# http://nokada.jin.gr.jp/ruby/hexfloat.rb
require 'stringio'

def show(a)
  d = a%1
  printf "%s %-20s %-20s %-20s %-20s\n", a.class, a.to_s, a.hex, d.hex, (1.0-d).hex
end

[5.00000000000007, 5.000000000000007, 5.0000000000000007, 5.00000000000000007,
 1.00000000000004, 1.000000000000004, 1.0000000000000004,
 1.99999999999999, 1.999999999999999, 1.9999999999999999].each(&method(:show))

StringIO.open(*DATA.read.unpack("m")) do |file|
  begin
    while a = Marshal.load(file)
      show(a)
    end
  rescue EOFError
  end
end

__END__
BAhmGjI0LjAwMDAwMDAwMDAwMDAwNAAAAQQIZhoyNy45OTk5OTk5OTk5OTk5OTYA//8ECGYaNDQu
MDAwMDAwMDAwMDAwMDA3AAABBAhmGjQ1Ljk5OTk5OTk5OTk5OTk5MwD//wQIZho0OC4wMDAwMDAw
MDAwMDAwMDcAAAEECGYaNTEuOTk5OTk5OTk5OTk5OTkzAP//BAhmGjU0LjAwMDAwMDAwMDAwMDAw
NwAAAQQIZho4My45OTk5OTk5OTk5OTk5ODYA//8=

$ ./ruby f.rb
Float 5.00000000000007     0x5.000000000013c    0x1.3cp-44           0xf.fffffffffec4p-4
Float 5.00000000000001     0x5.000000000002     0x2.0p-48            0xf.ffffffffffep-4
Float 5.0                  0x5.0000000000004    0x4.0p-52            0xf.fffffffffffcp-4
Float 5.0                  0x5.0                0x0.0p-4             0x1.0
Float 1.00000000000004     0x1.00000000000b4    0xb.4p-48            0xf.ffffffffff4cp-4
Float 1.0                  0x1.0000000000012    0x1.2p-48            0xf.ffffffffffeep-4
Float 1.0                  0x1.0000000000002    0x2.0p-52            0xf.fffffffffffep-4
Float 1.99999999999999     0x1.fffffffffffd3    0xf.ffffffffffd3p-4  0x2.dp-48
Float 2.0                  0x1.ffffffffffffb    0xf.fffffffffffbp-4  0x5.0p-52
Float 2.0                  0x2.0                0x0.0p-4             0x1.0
Float 24.0                 0x1.8000000000001p+4 0x1.0p-48            0xf.fffffffffffp-4
Float 28.0                 0x1.bffffffffffffp+4 0xf.fffffffffffp-4   0x1.0p-48
Float 44.0                 0x2.c000000000002p+4 0x2.0p-48            0xf.ffffffffffep-4
Float 46.0                 0x2.dfffffffffffep+4 0xf.ffffffffffep-4   0x2.0p-48
Float 48.0                 0x3.0000000000002p+4 0x2.0p-48            0xf.ffffffffffep-4
Float 52.0                 0x3.3fffffffffffep+4 0xf.ffffffffffep-4   0x2.0p-48
Float 54.0                 0x3.6000000000002p+4 0x2.0p-48            0xf.ffffffffffep-4
Float 84.0                 0x5.3fffffffffffcp+4 0xf.ffffffffffcp-4   0x4.0p-48

The range to be .f format is affected by also its precision.
This might be rather realistic.


Index: numeric.c
===================================================================
RCS file: /cvs/ruby/src/ruby/numeric.c,v
retrieving revision 1.106
diff -u -2 -p -r1.106 numeric.c
--- numeric.c	14 Apr 2004 04:06:25 -0000	1.106
+++ numeric.c	22 Apr 2004 04:34:22 -0000
@@ -517,8 +517,6 @@ flo_to_s(flt)
 	else fmt = "%.16e";
     }    
-    else if ((d1 = modf(value, &d2)) == 0) {
-	fmt = "%.1f";
-    }
     sprintf(buf, fmt, value);
+    if (!strchr(buf, '.')) strcat(buf, ".0");
 
     return rb_str_new2(buf);


-- 
Nobu Nakada