Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!linus!decvax!harpo!utah-cs!utah-gr!thomas
From: thomas@utah-gr.UUCP (Spencer W. Thomas)
Newsgroups: net.info-terms
Subject: Re: Z29 Termcap Entry
Message-ID: <883@utah-gr.UUCP>
Date: Tue, 16-Aug-83 00:25:00 EDT
Article-I.D.: utah-gr.883
Posted: Tue Aug 16 00:25:00 1983
Date-Received: Tue, 16-Aug-83 20:22:29 EDT
References: mit-eddi.597
Lines: 130


     What program would be silly enough to put the terminal into
  insert mode and shove stuff at it at 9600 baud you ask?  Gosling's
  Emacs.  Emacs seems to want to do the mathematically optimal thing in
  doing a redisplay rather than the practical thing.  When it is about
  to output a line on top of a line that is already on the screen,
  instead of just killing to the end of the line and outputing the new
  line, it compares the old line and the new line and if there are any
  similarities, it constructs the new line by deleting the text on the
  old line on the terminal that is already there and then inserting new
  text into the line to transform it into the new line that is to be
  displayed.  The Z29 does not act kindly to this.

There is a fix to this problem.  The termcap driver in Gosling's emacs
does not do a good job of computing the costs of inserting and deleting
characters.  Here is a diff listing (the numbers will be off, that's why
I did it with context) which fixes the problem.  It also fixes a long
standing problem (which is in ALL the terminal drivers) of computing the
"baud factor".  The formula used in the stock emacs is
	1) Special case to the Concept-100 and is "based on an analysis
		of the interrupt routine" in it, therefore not necessarily
		applicable to other terminals, and
	2) negative at 19.2k baud.
I have replaced it with a simple, straightforward calculation which seems
to do a pretty good job.

The diff listing follows.

=Spencer

*** old
--- new
***************
*** 14,15
  #include <stdio.h>
  #include "config.h"

--- 14,16 -----
  #include <stdio.h>
+ #include <ctype.h>
  #include "config.h"
***************
*** 230,233
      PC = 0;
!     BaudFactor = 1 / (1 - (.45 +.3 * BaudRate / 9600.))
! 	* (BaudRate / 10000.);
      if (CursStr == 0 || UP == 0 || ELstr == 0 || ESstr == 0) {

--- 235,237 -----
      PC = 0;
!     BaudFactor = BaudRate / 10000.;
      if (CursStr == 0 || UP == 0 || ELstr == 0 || ESstr == 0) {
***************
*** 240,243
      }
!     tt.t_ILmf = BaudFactor * 0.75;
!     tt.t_ILov = ILstr ? 2 : MissingFeature;
      if (!ILstr)

--- 244,251 -----
      }
!     if (ILstr)
! 	costof(ILstr, &ov, &mf);
!     else
! 	ov = mf = MissingFeature;
!     tt.t_ILmf = mf;
!     tt.t_ILov = ov;
      if (!ILstr)
***************
*** 247,252
      if (ICstr && DCstr) {
! 	tt.t_ICov = 1;
! 	tt.t_ICov = 4;
! 	tt.t_DCmf = 2;
! 	tt.t_DCov = 0;
      }

--- 255,267 -----
      if (ICstr && DCstr) {
! 	costof(ICstr, &ov, &mf);
! 	tt.t_ICov = ov + (ICPstr ? mf : 0);
! 	if (ICPstr)
! 	    costof(ICPstr, &ov, &mf);
! 	else
! 	    ov = mf + 1;
! 	tt.t_ICmf = ov;
! 
! 	tt.t_DCov = tt.t_ICov;
! 	costof(DCstr, &ov, &mf);
! 	tt.t_DCmf = ov + mf;
      }
***************
*** 253,254
      else {
!  	tt.t_ICov = MissingFeature;
  	tt.t_ICov = MissingFeature;

--- 268,270 -----
      else {
! 	tt.t_ICmf = MissingFeature;
  	tt.t_ICov = MissingFeature;
***************
*** 263,264
  
  

--- 278,286 -----
  
+ static
+ costof (str, ov, mf)
+ char *str;
+ int *ov, *mf;
+ {
+     register char *cp;
+     int pad;
+     *ov = *mf = pad = 0;
+     for (cp = str; isdigit(*cp); cp++)
+ 	pad = pad * 10 + (*cp - '0');
+     if (*cp == '*')
+     {
+ 	*mf = pad * BaudFactor;
+ 	cp++;
+     }
+     else
+ 	*ov = pad;
+     *ov += strlen(cp);
+     return *ov;
+ }
+ 
  static