/* $OpenBSD: display.c,v 1.23 2006/03/04 06:58:11 otto Exp $	 */

/*
 *  Top users/processes display for Unix
 *  Version 3
 *
 * Copyright (c) 1984, 1989, William LeFebvre, Rice University
 * Copyright (c) 1989, 1990, 1992, William LeFebvre, Northwestern University
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR OR HIS EMPLOYER BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/*
 *  This file contains the routines that display information on the screen.
 *  Each section of the screen has two routines:  one for initially writing
 *  all constant and dynamic text, and one for only updating the text that
 *  changes.  The prefix "i_" is used on all the "initial" routines and the
 *  prefix "u_" is used for all the "updating" routines.
 *
 *  ASSUMPTIONS:
 *        None of the "i_" routines use any of the termcap capabilities.
 *        In this way, those routines can be safely used on terminals that
 *        have minimal (or nonexistent) terminal capabilities.
 *
 *        The routines are called in this order:  *_loadave, i_timeofday,
 *        *_procstates, *_cpustates, *_memory, *_message, *_header,
 *        *_process, u_endscreen.
 */

#include <sys/types.h>
#include <sys/time.h>
#include <sys/sched.h>
#include <stdio.h>
#include <ctype.h>
#include <err.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <term.h>
#include <time.h>
#include <unistd.h>
#include <stdarg.h>

#include "screen.h"		/* interface to screen package */
#include "layout.h"		/* defines for screen position layout */
#include "display.h"
#include "top.h"
#include "top.local.h"
#include "boolean.h"
#include "machine.h"		/* we should eliminate this!!! */
#include "utils.h"

#ifdef DEBUG
FILE           *debug;
#endif

static pid_t    lmpid = 0;
static int      last_hi = 0;	/* used in u_process and u_endscreen */
static int      lastline = 0;
static int      display_width = MAX_COLS;

static char    *cpustates_tag(int);
static int      string_count(char **);
static void     summary_format(char *, size_t, int *, char **);
static void     line_update(char *, char *, int, int);

#define lineindex(l) ((l)*display_width)

/* things initialized by display_init and used throughout */

/* buffer of proc information lines for display updating */
char           *screenbuf = NULL;

static char   **procstate_names;
static char   **cpustate_names;
static char   **memory_names;

static int      num_procstates;
static int      num_cpustates;

static int     *lprocstates;
static int64_t **lcpustates;

static int     *cpustate_columns;
static int      cpustate_total_length;

/* display ips */
int y_mem;
int y_message;
int y_header;
int y_idlecursor;
int y_procs;
extern int ncpu;
int Header_lines;

static enum {
	OFF, ON, ERASE
} header_status = ON;

int
display_resize(void)
{
	int display_lines;

	/* first, deallocate any previous buffer that may have been there */
	if (screenbuf != NULL)
		free(screenbuf);

	/* calculate the current dimensions */
	/* if operating in "dumb" mode, we only need one line */
	display_lines = smart_terminal ? screen_length - Header_lines : 1;

	/*
	 * we don't want more than MAX_COLS columns, since the
	 * machine-dependent modules make static allocations based on
	 * MAX_COLS and we don't want to run off the end of their buffers
	 */
	display_width = screen_width;
	if (display_width >= MAX_COLS)
		display_width = MAX_COLS - 1;

	/* now, allocate space for the screen buffer */
	screenbuf = malloc(display_lines * display_width + 1);
	if (screenbuf == NULL)
		return (-1);

	/* return number of lines available */
	/* for dumb terminals, pretend like we can show any amount */
	return (smart_terminal ? display_lines : Largest);
}

int
display_init(struct statics * statics)
{
	int display_lines, *ip, i, cpu;
	char **pp;

	y_mem = 2 + ncpu;
	y_message = 3 + ncpu;
	y_header = 4 + ncpu;
	y_idlecursor = 3 + ncpu;
	y_procs = 5 + ncpu;
	Header_lines = 5 + ncpu;

	/* call resize to do the dirty work */
	display_lines = display_resize();

	/* only do the rest if we need to */
	if (display_lines > -1) {
		/* save pointers and allocate space for names */
		procstate_names = statics->procstate_names;
		num_procstates = string_count(procstate_names);
		lprocstates = malloc(num_procstates * sizeof(int));
		if (lprocstates == NULL)
			err(1, NULL);

		cpustate_names = statics->cpustate_names;
		num_cpustates = string_count(cpustate_names);
		lcpustates = malloc(ncpu * sizeof(int64_t *));
		if (lcpustates == NULL)
			err(1, NULL);
		for (cpu = 0; cpu < ncpu; cpu++) {
			lcpustates[cpu] = malloc(num_cpustates * sizeof(int64_t));
			if (lcpustates[cpu] == NULL)
				err(1, NULL);
		}
		
		cpustate_columns = malloc(num_cpustates * sizeof(int));
		if (cpustate_columns == NULL)
			err(1, NULL);

		memory_names = statics->memory_names;

		/* calculate starting columns where needed */
		cpustate_total_length = 0;
		pp = cpustate_names;
		ip = cpustate_columns;
		while (*pp != NULL) {
			if ((i = strlen(*pp++)) > 0) {
				*ip++ = cpustate_total_length;
				cpustate_total_length += i + 8;
			}
		}
	}
	/* return number of lines available */
	return (display_lines);
}

void
i_loadave(pid_t mpid, double *avenrun)
{
	int i;

	/* i_loadave also clears the screen, since it is first */
	clear();

	/* mpid == -1 implies this system doesn't have an _mpid */
	if (mpid != -1)
		printf("last pid: %5ld;  ", (long) mpid);

	printf("load averages");

	for (i = 0; i < 3; i++)
		printf("%c %5.2f", i == 0 ? ':' : ',', avenrun[i]);

	lmpid = mpid;
}

void
u_loadave(pid_t mpid, double *avenrun)
{
	int i;

	if (mpid != -1) {
		/* change screen only when value has really changed */
		if (mpid != lmpid) {
			Move_to(x_lastpid, y_lastpid);
			printf("%5ld", (long) mpid);
			lmpid = mpid;
		}
		/* i remembers x coordinate to move to */
		i = x_loadave;
	} else
		i = x_loadave_nompid;

	/* move into position for load averages */
	Move_to(i, y_loadave);

	/* display new load averages */
	/* we should optimize this and only display changes */
	for (i = 0; i < 3; i++)
		printf("%s%5.2f", i == 0 ? "" : ", ", avenrun[i]);
}

/*
 *  Display the current time.
 *  "ctime" always returns a string that looks like this:
 *
 *	Sun Sep 16 01:03:52 1973
 *      012345678901234567890123
 *	          1         2
 *
 *  We want indices 11 thru 18 (length 8).
 */

void
i_timeofday(time_t * tod)
{

	if (smart_terminal) {
		Move_to(screen_width - 8, 0);
	} else {
		if (fputs("    ", stdout) == EOF)
			exit(1);
	}
#ifdef DEBUG
	{
		char *foo;
		foo = ctime(tod);
		if (fputs(foo, stdout) == EOF)
			exit(1);
	}
#endif
	printf("%-8.8s\n", &(ctime(tod)[11]));
	lastline = 1;
}

static int      ltotal = 0;
static char     procstates_buffer[MAX_COLS];

/*
 *  *_procstates(total, brkdn, names) - print the process summary line
 *
 *  Assumptions:  cursor is at the beginning of the line on entry
 *		  lastline is valid
 */
void
i_procstates(int total, int *brkdn)
{
	int i;

	/* write current number of processes and remember the value */
	printf("%d processes:", total);
	ltotal = total;

	/* put out enough spaces to get to column 15 */
	i = digits(total);
	while (i++ < 4) {
		if (putchar(' ') == EOF)
			exit(1);
	}

	/* format and print the process state summary */
	summary_format(procstates_buffer, sizeof(procstates_buffer), brkdn,
	    procstate_names);
	if (fputs(procstates_buffer, stdout) == EOF)
		exit(1);

	/* save the numbers for next time */
	memcpy(lprocstates, brkdn, num_procstates * sizeof(int));
}

void
u_procstates(int total, int *brkdn)
{
	static char new[MAX_COLS];
	int i;

	/* update number of processes only if it has changed */
	if (ltotal != total) {
		/* move and overwrite */
#if (x_procstate == 0)
		Move_to(x_procstate, y_procstate);
#else
		/* cursor is already there...no motion needed */
		/* assert(lastline == 1); */
#endif
		printf("%d", total);

		/* if number of digits differs, rewrite the label */
		if (digits(total) != digits(ltotal)) {
			if (fputs(" processes:", stdout) == EOF)
				exit(1);
			/* put out enough spaces to get to column 15 */
			i = digits(total);
			while (i++ < 4) {
				if (putchar(' ') == EOF)
					exit(1);
			}
			/* cursor may end up right where we want it!!! */
		}
		/* save new total */
		ltotal = total;
	}
	/* see if any of the state numbers has changed */
	if (memcmp(lprocstates, brkdn, num_procstates * sizeof(int)) != 0) {
		/* format and update the line */
		summary_format(new, sizeof(new), brkdn, procstate_names);
		line_update(procstates_buffer, new, x_brkdn, y_brkdn);
		memcpy(lprocstates, brkdn, num_procstates * sizeof(int));
	}
}

/*
 *  *_cpustates(states, names) - print the cpu state percentages
 *
 *  Assumptions:  cursor is on the PREVIOUS line
 */

static int      cpustates_column;

/* cpustates_tag() calculates the correct tag to use to label the line */

static char *
cpustates_tag(int cpu)
{
	static char *tag;
	static int cpulen, old_width;
	int i;

	if (cpulen == 0 && ncpu > 1) {
		/* compute length of the cpu string */
		for (i = ncpu; i > 0; cpulen++, i /= 10)
			continue;
	}

	if (old_width == screen_width) {
		if (ncpu > 1) {
			/* just store the cpu number in the tag */
			i = tag[3 + cpulen];
			snprintf(tag + 3, cpulen + 1, "%.*d", cpulen, cpu);
			tag[3 + cpulen] = i;
		}
	} else {
		/*
		 * use a long tag if it will fit, otherwise use short one.
		 */
		free(tag);
		if (cpustate_total_length + 10 + cpulen >= screen_width)
			i = asprintf(&tag, "CPU%.*d: ", cpulen, cpu);
		else
			i = asprintf(&tag, "CPU%.*d states: ", cpulen, cpu);
		if (i == -1)
			tag = NULL;
		else {
			cpustates_column = strlen(tag);
			old_width = screen_width;
		}
	}
	return (tag);
}

void
i_cpustates(int64_t *ostates)
{
	int i, cpu, value;
	int64_t *states;
	char **names = cpustate_names, *thisname;

	for (cpu = 0; cpu < ncpu; cpu++) {
		/* print tag and bump lastline */
		printf("\n%s", cpustates_tag(cpu));
		lastline++;

		/* now walk thru the names and print the line */
		names = cpustate_names;
		i = 0;
		states = ostates + (CPUSTATES * cpu);
		while ((thisname = *names++) != NULL) {
			if (*thisname != '\0') {
				/* retrieve the value and remember it */
				value = *states++;

				/* if percentage is >= 1000, print it as 100% */
				printf((value >= 1000 ? "%s%4.0f%% %s" :
				    "%s%4.1f%% %s"), i++ == 0 ? "" : ", ",
				    ((float) value) / 10., thisname);
			}
		}

		/* copy over values into "last" array */
		memcpy(lcpustates[cpu], ostates, num_cpustates * sizeof(int64_t));
	}
}

void
u_cpustates(int64_t *ostates)
{
	char **names, *thisname;
	int cpu, value, *colp;
	int64_t *lp, *states;

	for (cpu = 0; cpu < ncpu; cpu++) {
		lastline = y_cpustates + cpu;
		states = ostates + (CPUSTATES * cpu);
		Move_to(cpustates_column, lastline);
		lp = lcpustates[cpu];
		colp = cpustate_columns;

		/* we could be much more optimal about this */
		names = cpustate_names;
		while ((thisname = *names++) != NULL) {
			if (*thisname != '\0') {
				/* did the value change since last time? */
				if (*lp != *states) {
					/* yes, move and change */
					lastline = y_cpustates + cpu;
					Move_to(cpustates_column + *colp,
					    lastline);

					/* retrieve value and remember it */
					value = *states;

					/* if percentage is >= 1000,
					 * print it as 100%
					 */
					printf((value >= 1000 ? "%4.0f" :
					    "%4.1f"), ((double) value) / 10.);

					/* remember it for next time */
					*lp = *states;
				}
			}
			/* increment and move on */
			lp++;
			states++;
			colp++;
		}
	}
}

static char     memory_buffer[MAX_COLS];

/*
 *  *_memory(stats) - print "Memory: " followed by the memory summary string
 *
 *  Assumptions:  cursor is on "lastline"
 *                for i_memory ONLY: cursor is on the previous line
 */
void
i_memory(int *stats)
{
	if (fputs("\nMemory: ", stdout) == EOF)
		exit(1);
	lastline++;

	/* format and print the memory summary */
	summary_format(memory_buffer, sizeof(memory_buffer), stats,
	    memory_names);
	if (fputs(memory_buffer, stdout) == EOF)
		exit(1);
}

void
u_memory(int *stats)
{
	static char new[MAX_COLS];

	/* format the new line */
	summary_format(new, sizeof(new), stats, memory_names);
	line_update(memory_buffer, new, x_mem, y_mem);
}

/*
 *  *_message() - print the next pending message line, or erase the one
 *                that is there.
 *
 *  Note that u_message is (currently) the same as i_message.
 *
 *  Assumptions:  lastline is consistent
 */

/*
 *  i_message is funny because it gets its message asynchronously (with
 *	respect to screen updates).
 */

static char     next_msg[MAX_COLS + 5];
static int      msglen = 0;
/*
 * Invariant: msglen is always the length of the message currently displayed
 * on the screen (even when next_msg doesn't contain that message).
 */

void
i_message(void)
{
	while (lastline < y_message) {
		if (fputc('\n', stdout) == EOF)
			exit(1);
		lastline++;
	}
	if (next_msg[0] != '\0') {
		standout(next_msg);
		msglen = strlen(next_msg);
		next_msg[0] = '\0';
	} else if (msglen > 0) {
		(void) clear_eol(msglen);
		msglen = 0;
	}
}

void
u_message(void)
{
	i_message();
}

static int      header_length;

/*
 *  *_header(text) - print the header for the process area
 *
 *  Assumptions:  cursor is on the previous line and lastline is consistent
 */

void
i_header(char *text)
{
	header_length = strlen(text);
	if (header_status == ON) {
		if (putchar('\n') == EOF)
			exit(1);
		if (fputs(text, stdout) == EOF)
			exit(1);
		lastline++;
	} else if (header_status == ERASE) {
		header_status = OFF;
	}
}

/* ARGSUSED */
void
u_header(char *text)
{
	if (header_status == ERASE) {
		if (putchar('\n') == EOF)
			exit(1);
		lastline++;
		clear_eol(header_length);
		header_status = OFF;
	}
}

/*
 *  *_process(line, thisline) - print one process line
 *
 *  Assumptions:  lastline is consistent
 */

void
i_process(int line, char *thisline)
{
	char *base;
	size_t len;

	/* make sure we are on the correct line */
	while (lastline < y_procs + line) {
		if (putchar('\n') == EOF)
			exit(1);
		lastline++;
	}

	/* truncate the line to conform to our current screen width */
	thisline[display_width] = '\0';

	/* write the line out */
	if (fputs(thisline, stdout) == EOF)
		exit(1);

	/* copy it in to our buffer */
	base = smart_terminal ? screenbuf + lineindex(line) : screenbuf;
	len = strlcpy(base, thisline, display_width);
	if (len < (size_t)display_width) {
		/* zero fill the rest of it */
		memset(base + len, 0, display_width - len);
	}
}

void
u_process(int linenum, char *linebuf)
{
	int screen_line = linenum + Header_lines;
	char *bufferline;
	size_t len;

	/* remember a pointer to the current line in the screen buffer */
	bufferline = &screenbuf[lineindex(linenum)];

	/* truncate the line to conform to our current screen width */
	linebuf[display_width] = '\0';
	bufferline[display_width] = '\0';

	/* is line higher than we went on the last display? */
	if (linenum >= last_hi) {
		/* yes, just ignore screenbuf and write it out directly */
		/* get positioned on the correct line */
		if (screen_line - lastline == 1) {
			if (putchar('\n') == EOF)
				exit(1);
			lastline++;
		} else {
			Move_to(0, screen_line);
			lastline = screen_line;
		}

		/* now write the line */
		if (fputs(linebuf, stdout) == EOF)
			exit(1);

		/* copy it in to the buffer */
		len = strlcpy(bufferline, linebuf, display_width);
		if (len < (size_t)display_width) {
			/* zero fill the rest of it */
			memset(bufferline + len, 0, display_width - len);
		}
	} else {
		line_update(bufferline, linebuf, 0, linenum + Header_lines);
	}
}

void
u_endscreen(int hi)
{
	int screen_line = hi + Header_lines, i;

	if (smart_terminal) {
		if (hi < last_hi) {
			/* need to blank the remainder of the screen */
			/*
			 * but only if there is any screen left below this
			 * line
			 */
			if (lastline + 1 < screen_length) {
				/*
				 * efficiently move to the end of currently
				 * displayed info
				 */
				if (screen_line - lastline < 5) {
					while (lastline < screen_line) {
						if (putchar('\n') == EOF)
							exit(1);
						lastline++;
					}
				} else {
					Move_to(0, screen_line);
					lastline = screen_line;
				}

				if (clear_to_end) {
					/* we can do this the easy way */
					putcap(clear_to_end);
				} else {
					/* use clear_eol on each line */
					i = hi;
					while ((void) clear_eol(strlen(&screenbuf[lineindex(i++)])), i < last_hi) {
						if (putchar('\n') == EOF)
							exit(1);
					}
				}
			}
		}
		last_hi = hi;

		/* move the cursor to a pleasant place */
		Move_to(x_idlecursor, y_idlecursor);
		lastline = y_idlecursor;
	} else {
		/*
		 * separate this display from the next with some vertical
		 * room
		 */
		if (fputs("\n\n", stdout) == EOF)
			exit(1);
	}
}

void
display_header(int t)
{
	if (t) {
		header_status = ON;
	} else if (header_status == ON) {
		header_status = ERASE;
	}
}

void
new_message(int type, const char *msgfmt,...)
{
	va_list ap;
	int i;

	va_start(ap, msgfmt);
	/* first, format the message */
	vsnprintf(next_msg, sizeof(next_msg), msgfmt, ap);
	va_end(ap);

	if (msglen > 0) {
		/* message there already -- can we clear it? */
		if (!overstrike) {
			/* yes -- write it and clear to end */
			i = strlen(next_msg);
			if ((type & MT_delayed) == 0) {
				if (type & MT_standout)
					standout(next_msg);
				else {
					if (fputs(next_msg, stdout) == EOF)
						exit(1);
				}
				(void) clear_eol(msglen - i);
				msglen = i;
				next_msg[0] = '\0';
			}
		}
	} else {
		if ((type & MT_delayed) == 0) {
			if (type & MT_standout)
				standout(next_msg);
			else {
				if (fputs(next_msg, stdout) == EOF)
					exit(1);
			}
			msglen = strlen(next_msg);
			next_msg[0] = '\0';
		}
	}
}

void
clear_message(void)
{
	if (clear_eol(msglen) == 1) {
		if (putchar('\r') == EOF)
			exit(1);
	}
}

int
readline(char *buffer, int size, int numeric)
{
	char *ptr = buffer, ch, cnt = 0, maxcnt = 0;
	extern volatile sig_atomic_t leaveflag;
	ssize_t len;

	/* allow room for null terminator */
	size -= 1;

	/* read loop */
	while ((fflush(stdout), (len = read(STDIN_FILENO, ptr, 1)) > 0)) {

		if (len == 0 || leaveflag) {
			end_screen();
			exit(0);
		}

		/* newline means we are done */
		if ((ch = *ptr) == '\n')
			break;

		/* handle special editing characters */
		if (ch == ch_kill) {
			/* kill line -- account for overstriking */
			if (overstrike)
				msglen += maxcnt;

			/* return null string */
			*buffer = '\0';
			if (putchar('\r') == EOF)
				exit(1);
			return (-1);
		} else if (ch == ch_erase) {
			/* erase previous character */
			if (cnt <= 0) {
				/* none to erase! */
				if (putchar('\7') == EOF)
					exit(1);
			} else {
				if (fputs("\b \b", stdout) == EOF)
					exit(1);
				ptr--;
				cnt--;
			}
		}
		/* check for character validity and buffer overflow */
		else if (cnt == size || (numeric && !isdigit(ch)) ||
		    !isprint(ch)) {
			/* not legal */
			if (putchar('\7') == EOF)
				exit(1);
		} else {
			/* echo it and store it in the buffer */
			if (putchar(ch) == EOF)
				exit(1);
			ptr++;
			cnt++;
			if (cnt > maxcnt)
				maxcnt = cnt;
		}
	}

	/* all done -- null terminate the string */
	*ptr = '\0';

	/* account for the extra characters in the message area */
	/* (if terminal overstrikes, remember the furthest they went) */
	msglen += overstrike ? maxcnt : cnt;

	/* return either inputted number or string length */
	if (putchar('\r') == EOF)
		exit(1);
	return (cnt == 0 ? -1 : numeric ? atoi(buffer) : cnt);
}

/* internal support routines */
static int
string_count(char **pp)
{
	int cnt;

	cnt = 0;
	while (*pp++ != NULL)
		cnt++;
	return (cnt);
}

#define	COPYLEFT(to, from)				\
	do {						\
		len = strlcpy((to), (from), left);	\
		if (len >= left)			\
			return;				\
		p += len;				\
		left -= len;				\
	} while (0)

static void
summary_format(char *buf, size_t left, int *numbers, char **names)
{
	char *p, *thisname;
	size_t len;
	int num;

	/* format each number followed by its string */
	p = buf;
	while ((thisname = *names++) != NULL) {
		/* get the number to format */
		num = *numbers++;

		if (num >= 0) {
			/* is this number in kilobytes? */
			if (thisname[0] == 'K') {
				/* yes: format it as a memory value */
				COPYLEFT(p, format_k(num));

				/*
				 * skip over the K, since it was included by
				 * format_k
				 */
				COPYLEFT(p, thisname + 1);
			} else if (num > 0) {
				len = snprintf(p, left, "%d%s", num, thisname);
				if (len == (size_t)-1 || len >= left)
					return;
				p += len;
				left -= len;
			}
		} else {
			/*
			 * Ignore negative numbers, but display corresponding
			 * string.
			 */
			COPYLEFT(p, thisname);
		}
	}

	/* if the last two characters in the string are ", ", delete them */
	p -= 2;
	if (p >= buf && p[0] == ',' && p[1] == ' ')
		*p = '\0';
}

static void
line_update(char *old, char *new, int start, int line)
{
	int ch, diff, newcol = start + 1, lastcol = start;
	char cursor_on_line = No, *current;

	/* compare the two strings and only rewrite what has changed */
	current = old;
#ifdef DEBUG
	fprintf(debug, "line_update, starting at %d\n", start);
	fputs(old, debug);
	fputc('\n', debug);
	fputs(new, debug);
	fputs("\n-\n", debug);
#endif

	/* start things off on the right foot		    */
	/* this is to make sure the invariants get set up right */
	if ((ch = *new++) != *old) {
		if (line - lastline == 1 && start == 0) {
			if (putchar('\n') == EOF)
				exit(1);
		} else
			Move_to(start, line);

		cursor_on_line = Yes;
		if (putchar(ch) == EOF)
			exit(1);
		*old = ch;
		lastcol = 1;
	}
	old++;

	/*
	 *  main loop -- check each character.  If the old and new aren't the
	 *	same, then update the display.  When the distance from the
	 *	current cursor position to the new change is small enough,
	 *	the characters that belong there are written to move the
	 *	cursor over.
	 *
	 *	Invariants:
	 *	    lastcol is the column where the cursor currently is sitting
	 *		(always one beyond the end of the last mismatch).
	 */
	do {
		if ((ch = *new++) != *old) {
			/* new character is different from old	  */
			/* make sure the cursor is on top of this character */
			diff = newcol - lastcol;
			if (diff > 0) {
				/*
				 * some motion is required--figure out which
				 * is shorter
				 */
				if (diff < 6 && cursor_on_line) {
					/*
					 * overwrite old stuff--get it out of
					 * the old buffer
					 */
					printf("%.*s", diff, &current[lastcol - start]);
				} else {
					/* use cursor addressing */
					Move_to(newcol, line);
					cursor_on_line = Yes;
				}
				/* remember where the cursor is */
				lastcol = newcol + 1;
			} else {
				/* already there, update position */
				lastcol++;
			}

			/* write what we need to */
			if (ch == '\0') {
				/*
				 * at the end--terminate with a
				 * clear-to-end-of-line
				 */
				(void) clear_eol(strlen(old));
			} else {
				/* write the new character */
				if (putchar(ch) == EOF)
					exit(1);
			}
			/* put the new character in the screen buffer */
			*old = ch;
		}
		/* update working column and screen buffer pointer */
		newcol++;
		old++;
	} while (ch != '\0');

	/* zero out the rest of the line buffer -- MUST BE DONE! */
	diff = display_width - newcol;
	if (diff > 0)
		memset(old, 0, diff);

	/* remember where the current line is */
	if (cursor_on_line)
		lastline = line;
}

/*
 *  printable(str) - make the string pointed to by "str" into one that is
 *	printable (i.e.: all ascii), by converting all non-printable
 *	characters into '?'.  Replacements are done in place and a pointer
 *	to the original buffer is returned.
 */
char *
printable(char *str)
{
	char *ptr, ch;

	ptr = str;
	while ((ch = *ptr) != '\0') {
		if (!isprint(ch))
			*ptr = '?';
		ptr++;
	}
	return (str);
}