/*  File   : _str2map.c
    Author : Richard A. O'Keefe.
    Updated: 20 April 1984
    Defines: _map_vec[], _str2map().

    _str2map(option, from, to) constructs a translation table.  If  from
    or to is NullS, the same string is used as last time, so if you want
    to translate a whole lot of strings using the same mapping you don't
    have to reconstruct it each time.  The options are

	0: initialise the map to the identity function,
	   then map each from[i] to the corresponding to[i].
	   If to[] is shorter than from[], its last character is
	   repeated as often as needed.

	1: as 0, but don't initialise the map.

	2: initialise the map to send every character to to[0],
	   then map each from[i] to itself.

    For example, to build a map which forces letters to lower case but
    sends everything else to blank, call

	_str2map(2, "abcdefghijklmnopqrstuvwxyz", " ");
	_str2map(1, "ABCDEFGHIJKLMNOPQRSTUVWXYZ", "abcdefghijklmnopqrstuvwxyz");

    Only strtrans() and strntrans() in this package  call  _str2map;  if
    you  want  to  build your own maps this way you can "fool" them into
    using it, as when the two strings are NullS they  don't  change  the
    map.   As an extra-special dubious *hack*, _map_vec has an extra NUL
    character at the end, so after calling _str2map(0, "", ""), you  can
    use  _map_vec+1 as a string of the 127 non-NUL characters (or if the
    _AlphabetSize is 256, of the 255 non-NUL characters).
*/

#include "strings.h"
#include "_str2map.h"

static	_char_	*oldFrom = "?";
static	char	*oldTo   = "?";

char	_map_vec[_AlphabetSize+1];

void _str2map(option, from, to)
    int option;
    register _char_ *from;
    register char *to;
    {
	register int i, c;

	if (from == NullS && to == NullS) return;
	if (from == NullS) from = oldFrom; else oldFrom = from;
	if (to   == NullS) to   = oldTo;   else oldTo   = to;
	switch (option) {
	    case 0:
		for (i = _AlphabetSize; --i >= 0; _map_vec[i] = i) ;
	    case 1:
		while (i = *from++) {
		    _map_vec[i] = *to++;
		    if (!*to) {
			c = *--to;
			while (i = *from++) _map_vec[i] = c;
			return;
		    }
		}
		return;
	    case 2:
		c = *to;
		for (i = _AlphabetSize; --i >= 0; _map_vec[i] = c) ;
		while (c = *from++) _map_vec[c] = c;
		return;
	}
    }