TIP #472: ADD SUPPORT FOR 0D RADIX PREFIX TO INTEGER LITERALS 
===============================================================
 Version:      $Revision: 1.8 $
 Author:       Venkat Iyer <venksi_at_gmail.com>
               Brian Griffin <brian_griffin_at_mentor.com>
 State:        Accepted
 Type:         Project
 Tcl-Version:  8.7
 Vote:         Done
 Created:      Thursday, 25 May 2017
 URL:          https://tip.tcl-lang.org472.html
 Post-History: 

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 ABSTRACT 
==========

 This TIP proposes adding support for a *0d* decimal radix prefix to 
 complement the existing *0x* hexidecimal, *0o* octal and *0b* binary 
 radix prefixes. 

 RATIONALE 
===========

 Verilog (and other Hardware Description Languages) always (or at least 
 since the 1995 LRM) had a way to specify a decimal number explicitly. 
 Verilog uses *'d343534* to mean decimal, VHDL actually allows any radix 
 from 2 to 16 using syntax, so you could explicitly force a decimal 
 interpretation using *10#343534#*. 

 Tcl now allows *0b* for binary in *expr* and *format*, which is similar 
 to *'b* in Verilog. And of course the *0x* prefix has always been 
 around. Another use case would be to prevent false parsing of leading 
 zeroes in *clock format*s as octal, without having to go through a 
 *scan*. 

 But a more elegant reason is that it makes the radix definition 
 consistent, so 

    1. all valid input radixes have a consistent unambiguous input 
       literal format, and 

    2. the *d* in *format %d* finally finds its complement in *scan*. 

 SPECIFICATION 
===============

 Extend the *TclParseNumber* function to recognize the prefixes *0d* and 
 *0D* as decimal integers. It will have the same semantics as *0x*, but 
 base 10 instead of base 16.  

 Also extend format command '#' flag to produce the appropriate "0d" for 
 the "%#d" conversion.  

 EXAMPLES 
==========

 It's an integer: 

      % expr {0d12 + 0d15}
      27
      % format "%#x" 0d1024
      0x400
      % format "%#d" 128
      0d128

 Errors same as other radix prefixes: 

      % expr { 0d317g }
      invalid bareword "0d317g"
      in expression " 0d317g ";
      should be "$0d317g" or "{0d317g}" or "0d317g(...)" or ...
      % expr { 0x1.53 }
      missing operator at _@_
      in expression " 0x1_@_.53 "
      % expr {0d7.23}
      missing operator at _@_
      in expression "0d7_@_.23"

 COMPATIBILITY 
===============

 Currently, literals beginning with *0d* and parsed as a number will 
 produce an error. Any code expecting such an error would fail to 
 produce an error an thus have a change in behavior. I would expect this 
 situation to be uncommon. 

 IMPLEMENTATION 
================

 An implementation can be found the fossil on the "bsg-0d-radix-prefix" 
 branch, including %#d conversion support. 

 COPYRIGHT 
===========

 This document has been placed in the public domain. 

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