Improve const-correctness of RE compiler

5 files changed, 97 insertions, 90 deletions

diff --git a/ChangeLog b/ChangeLog
index 77d4181..8e2e607 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,17 +1,23 @@
+2007-04-19  Donal K. Fellows  <donal.k.fellows@manchester.ac.uk>
+
+	* generic/regcomp.c, generic/regc_cvec.c, generic/regc_lex.c,
+	* generic/regc_locale.c: Improve the const-correctness of the RE
+	compiler.
+
 2007-04-18  Miguel Sofer  <msofer@users.sf.net>
 
-	* generic/tclExecute.c (INST_LSHIFT): fixed a mistake introduced
-	in version 1.266 ('=' became '=='), which effectively turned the
-	block that handles native shifts into dead code. This explains why
-	the testsuite did not pick this mistake. Rewrote to make the
-	intention clear.
+	* generic/tclExecute.c (INST_LSHIFT): fixed a mistake introduced in
+	version 1.266 ('=' became '=='), which effectively turned the block
+	that handles native shifts into dead code. This explains why the
+	testsuite did not pick this mistake. Rewrote to make the intention
+	clear.
 
 2007-04-18  Miguel Sofer  <msofer@users.sf.net>
 
 	* generic/tclInt.h (TclDecrRefCount): change the order of the
 	branches, use empty 'if ; else' to handle use in unbraced outer
 	if/else conditions (as already done in tcl.h)
-	
+
 2007-04-18  Miguel Sofer  <msofer@users.sf.net>
 
 	* generic/tclExecute.c: slight changes in Tcl_Obj management.
@@ -19,12 +25,11 @@
 2007-04-17  Kevin B. Kenny  <kennykb@acm.org>
 
 	* library/clock.tcl: Fixed the naming of
-	::tcl::clock::ReadZoneinfoFile because (yoicks!) it was in the
-	global namespace.
+	::tcl::clock::ReadZoneinfoFile because (yoicks!) it was in the global
+	namespace.
 	* doc/clock.n: Clarified the cases in which legacy time zone is
 	recognized. [Bug 1656002]
-	
-	
+
 2007-04-17  Miguel Sofer  <msofer@users.sf.net>
 
 	* generic/tclExecute.c: fixed checkInterp logic [Bug 1702212]
@@ -42,7 +47,7 @@
 	the [clock] command. [Bug 1690041]
 	* tests/clock.test: Added rudimentary test cases for unique-prefix
 	matching of keywords.
-	
+
 2007-04-14  Miguel Sofer  <msofer@users.sf.net>
 
 	* generic/tclExecute.c: removed some code at INST_EXPAND_SKTOP that
@@ -54,7 +59,7 @@
 	OBJ_AT_DEPTH(n) and CURR_DEPTH that remove all direct references to
 	tosPtr from TEBC (after initialisation and the code at the label
 	cleanupV_pushObjResultPtr).
-	
+
 2007-04-11  Miguel Sofer  <msofer@users.sf.net>
 
 	* generic/tclCompCmds.c: moved all exceptDepth management to the
diff --git a/generic/regc_cvec.c b/generic/regc_cvec.c
index 55d087a..a0a14c2 100644
--- a/generic/regc_cvec.c
+++ b/generic/regc_cvec.c
@@ -28,6 +28,11 @@
  * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
+
+/*
+ * Notes:
+ * Only (selected) functions in _this_ file should treat chr* as non-constant.
+ */
 
 /*
  - newcvec - allocate a new cvec
@@ -39,14 +44,13 @@ newcvec(
     int nranges,		/* ... and this many ranges... */
     int nmcces)			/* ... and this many MCCEs */
 {
-    size_t n;
-    size_t nc;
+    size_t n, nc;
     struct cvec *cv;
 
     nc = (size_t)nchrs + (size_t)nmcces*(MAXMCCE+1) + (size_t)nranges*2;
     n = sizeof(struct cvec) + (size_t)(nmcces-1)*sizeof(chr *)
 	    + nc*sizeof(chr);
-    cv = (struct cvec *)MALLOC(n);
+    cv = (struct cvec *) MALLOC(n);
     if (cv == NULL) {
 	return NULL;
     }
@@ -120,19 +124,17 @@ addrange(
 
 /*
  - addmcce - add an MCCE to a cvec
- ^ static VOID addmcce(struct cvec *, chr *, chr *);
+ ^ static VOID addmcce(struct cvec *, const chr *, const chr *);
  */
 
 static void
 addmcce(
     struct cvec *cv,		/* character vector */
-    chr *startp,		/* beginning of text */
-    chr *endp)			/* just past end of text */
+    const chr *startp,		/* beginning of text */
+    const chr *endp)		/* just past end of text */
 {
-    int len;
-    int i;
-    chr *s;
-    chr *d;
+    int len, i;
+    const chr *s, *d;
 
     if (startp == NULL && endp == NULL) {
 	return;
@@ -162,7 +164,7 @@ haschr(
     pchr c)			/* character to test for */
 {
     int i;
-    chr *p;
+    const chr *p;
 
     for (p = cv->chrs, i = cv->nchrs; i > 0; p++, i--) {
 	if (*p == c) {
diff --git a/generic/regc_lex.c b/generic/regc_lex.c
index cc02e9d..f57779d 100644
--- a/generic/regc_lex.c
+++ b/generic/regc_lex.c
@@ -207,13 +207,13 @@ prefixes(
  - lexnest - "call a subroutine", interpolating string at the lexical level
  * Note, this is not a very general facility.  There are a number of
  * implicit assumptions about what sorts of strings can be subroutines.
- ^ static VOID lexnest(struct vars *, chr *, chr *);
+ ^ static VOID lexnest(struct vars *, const chr *, const chr *);
  */
 static void
 lexnest(
     struct vars *v,
-    chr *beginp,		/* start of interpolation */
-    chr *endp)			/* one past end of interpolation */
+    const chr *beginp,		/* start of interpolation */
+    const chr *endp)		/* one past end of interpolation */
 {
     assert(v->savenow == NULL);	/* only one level of nesting */
     v->savenow = v->now;
@@ -226,47 +226,47 @@ lexnest(
  * string constants to interpolate as expansions of things like \d
  */
 
-static chr backd[] = {		/* \d */
+static const chr backd[] = {	/* \d */
     CHR('['), CHR('['), CHR(':'),
     CHR('d'), CHR('i'), CHR('g'), CHR('i'), CHR('t'),
     CHR(':'), CHR(']'), CHR(']')
 };
-static chr backD[] = {		/* \D */
+static const chr backD[] = {	/* \D */
     CHR('['), CHR('^'), CHR('['), CHR(':'),
     CHR('d'), CHR('i'), CHR('g'), CHR('i'), CHR('t'),
     CHR(':'), CHR(']'), CHR(']')
 };
-static chr brbackd[] = {	/* \d within brackets */
+static const chr brbackd[] = {	/* \d within brackets */
     CHR('['), CHR(':'),
     CHR('d'), CHR('i'), CHR('g'), CHR('i'), CHR('t'),
     CHR(':'), CHR(']')
 };
-static chr backs[] = {		/* \s */
+static const chr backs[] = {	/* \s */
     CHR('['), CHR('['), CHR(':'),
     CHR('s'), CHR('p'), CHR('a'), CHR('c'), CHR('e'),
     CHR(':'), CHR(']'), CHR(']')
 };
-static chr backS[] = {		/* \S */
+static const chr backS[] = {	/* \S */
     CHR('['), CHR('^'), CHR('['), CHR(':'),
     CHR('s'), CHR('p'), CHR('a'), CHR('c'), CHR('e'),
     CHR(':'), CHR(']'), CHR(']')
 };
-static chr brbacks[] = {	/* \s within brackets */
+static const chr brbacks[] = {	/* \s within brackets */
     CHR('['), CHR(':'),
     CHR('s'), CHR('p'), CHR('a'), CHR('c'), CHR('e'),
     CHR(':'), CHR(']')
 };
-static chr backw[] = {		/* \w */
+static const chr backw[] = {	/* \w */
     CHR('['), CHR('['), CHR(':'),
     CHR('a'), CHR('l'), CHR('n'), CHR('u'), CHR('m'),
     CHR(':'), CHR(']'), CHR('_'), CHR(']')
 };
-static chr backW[] = {		/* \W */
+static const chr backW[] = {	/* \W */
     CHR('['), CHR('^'), CHR('['), CHR(':'),
     CHR('a'), CHR('l'), CHR('n'), CHR('u'), CHR('m'),
     CHR(':'), CHR(']'), CHR('_'), CHR(']')
 };
-static chr brbackw[] = {	/* \w within brackets */
+static const chr brbackw[] = {	/* \w within brackets */
     CHR('['), CHR(':'),
     CHR('a'), CHR('l'), CHR('n'), CHR('u'), CHR('m'),
     CHR(':'), CHR(']'), CHR('_')
@@ -748,7 +748,7 @@ lexescape(
     static chr esc[] = {
 	CHR('E'), CHR('S'), CHR('C')
     };
-    chr *save;
+    const chr *save;
 
     assert(v->cflags&REG_ADVF);
 
@@ -1086,7 +1086,7 @@ static void
 skip(
     struct vars *v)
 {
-    chr *start = v->now;
+    const chr *start = v->now;
 
     assert(v->cflags&REG_EXPANDED);
 
@@ -1128,11 +1128,11 @@ newline(void)
  * This helps confine use of CHR to this source file.  Beware that the caller
  * knows how long the sequence is.
  ^ #ifdef REG_DEBUG
- ^ static chr *ch(NOPARMS);
+ ^ static const chr *ch(NOPARMS);
  ^ #endif
  */
 #ifdef REG_DEBUG
-static chr *
+static const chr *
 ch(void)
 {
     static chr chstr[] = { CHR('c'), CHR('h'), CHR('\0') };
@@ -1145,13 +1145,13 @@ ch(void)
  - chrnamed - return the chr known by a given (chr string) name
  * The code is a bit clumsy, but this routine gets only such specialized
  * use that it hardly matters.
- ^ static chr chrnamed(struct vars *, chr *, chr *, pchr);
+ ^ static chr chrnamed(struct vars *, const chr *, const chr *, pchr);
  */
 static chr
 chrnamed(
     struct vars *v,
-    chr *startp,		/* start of name */
-    chr *endp,			/* just past end of name */
+    const chr *startp,		/* start of name */
+    const chr *endp,		/* just past end of name */
     pchr lastresort)		/* what to return if name lookup fails */
 {
     celt c;
diff --git a/generic/regc_locale.c b/generic/regc_locale.c
index be01dfb..b08c300 100644
--- a/generic/regc_locale.c
+++ b/generic/regc_locale.c
@@ -9,12 +9,12 @@
  * See the file "license.terms" for information on usage and redistribution of
  * this file, and for a DISCLAIMER OF ALL WARRANTIES.
  *
- * RCS: @(#) $Id: regc_locale.c,v 1.16 2007/04/10 22:01:06 dkf Exp $
+ * RCS: @(#) $Id: regc_locale.c,v 1.17 2007/04/19 09:00:55 dkf Exp $
  */
 
 /* ASCII character-name table */
 
-static struct cname {
+static const struct cname {
     const char *name;
     const char code;
 } cnames[] = {
@@ -133,7 +133,7 @@ typedef struct crange {
 
 /* Unicode: alphabetic characters */
 
-static crange alphaRangeTable[] = {
+static const crange alphaRangeTable[] = {
     {0x0041, 0x005a}, {0x0061, 0x007a}, {0x00c0, 0x00d6}, {0x00d8, 0x00f6},
     {0x00f8, 0x021f}, {0x0222, 0x0233}, {0x0250, 0x02ad}, {0x02b0, 0x02b8},
     {0x02bb, 0x02c1}, {0x02e0, 0x02e4}, {0x0388, 0x038a}, {0x038e, 0x03a1},
@@ -181,7 +181,7 @@ static crange alphaRangeTable[] = {
 
 #define NUM_ALPHA_RANGE (sizeof(alphaRangeTable)/sizeof(crange))
 
-static chr alphaCharTable[] = {
+static const chr alphaCharTable[] = {
     0x00aa, 0x00b5, 0x00ba, 0x02d0, 0x02d1, 0x02ee, 0x037a, 0x0386, 0x038c,
     0x04c7, 0x04c8, 0x04cb, 0x04cc, 0x04f8, 0x04f9, 0x0559, 0x06d5, 0x06e5,
     0x06e6, 0x0710, 0x093d, 0x0950, 0x098f, 0x0990, 0x09b2, 0x09dc, 0x09dd,
@@ -203,7 +203,7 @@ static chr alphaCharTable[] = {
  * Unicode: decimal digit characters
  */
 
-static crange digitRangeTable[] = {
+static const crange digitRangeTable[] = {
     {0x0030, 0x0039}, {0x0660, 0x0669}, {0x06f0, 0x06f9}, {0x0966, 0x096f},
     {0x09e6, 0x09ef}, {0x0a66, 0x0a6f}, {0x0ae6, 0x0aef}, {0x0b66, 0x0b6f},
     {0x0be7, 0x0bef}, {0x0c66, 0x0c6f}, {0x0ce6, 0x0cef}, {0x0d66, 0x0d6f},
@@ -221,7 +221,7 @@ static crange digitRangeTable[] = {
  * Unicode: punctuation characters.
  */
 
-static crange punctRangeTable[] = {
+static const crange punctRangeTable[] = {
     {0x0021, 0x0023}, {0x0025, 0x002a}, {0x002c, 0x002f}, {0x005b, 0x005d},
     {0x055a, 0x055f}, {0x066a, 0x066d}, {0x0700, 0x070d}, {0x0f04, 0x0f12},
     {0x0f3a, 0x0f3d}, {0x104a, 0x104f}, {0x1361, 0x1368}, {0x16eb, 0x16ed},
@@ -233,7 +233,7 @@ static crange punctRangeTable[] = {
 
 #define NUM_PUNCT_RANGE (sizeof(punctRangeTable)/sizeof(crange))
 
-static chr punctCharTable[] = {
+static const chr punctCharTable[] = {
     0x003a, 0x003b, 0x003f, 0x0040, 0x005f, 0x007b, 0x007d, 0x00a1, 0x00ab,
     0x00ad, 0x00b7, 0x00bb, 0x00bf, 0x037e, 0x0387, 0x0589, 0x058a, 0x05be,
     0x05c0, 0x05c3, 0x05f3, 0x05f4, 0x060c, 0x061b, 0x061f, 0x06d4, 0x0964,
@@ -249,13 +249,13 @@ static chr punctCharTable[] = {
  * Unicode: white space characters.
  */
 
-static crange spaceRangeTable[] = {
+static const crange spaceRangeTable[] = {
     {0x0009, 0x000d}, {0x2000, 0x200b}
 };
 
 #define NUM_SPACE_RANGE (sizeof(spaceRangeTable)/sizeof(crange))
 
-static chr spaceCharTable[] = {
+static const chr spaceCharTable[] = {
     0x0020, 0x00a0, 0x1680, 0x2028, 0x2029, 0x202f, 0x3000
 };
 
@@ -265,7 +265,7 @@ static chr spaceCharTable[] = {
  * Unicode: lowercase characters
  */
 
-static crange lowerRangeTable[] = {
+static const crange lowerRangeTable[] = {
     {0x0061, 0x007a}, {0x00df, 0x00f6}, {0x00f8, 0x00ff}, {0x017e, 0x0180},
     {0x0199, 0x019b}, {0x01bd, 0x01bf}, {0x0250, 0x02ad}, {0x03ac, 0x03ce},
     {0x03d5, 0x03d7}, {0x03ef, 0x03f3}, {0x0430, 0x045f}, {0x0561, 0x0587},
@@ -278,7 +278,7 @@ static crange lowerRangeTable[] = {
 
 #define NUM_LOWER_RANGE (sizeof(lowerRangeTable)/sizeof(crange))
 
-static chr lowerCharTable[] = {
+static const chr lowerCharTable[] = {
     0x00aa, 0x00b5, 0x00ba, 0x0101, 0x0103, 0x0105, 0x0107, 0x0109, 0x010b,
     0x010d, 0x010f, 0x0111, 0x0113, 0x0115, 0x0117, 0x0119, 0x011b, 0x011d,
     0x011f, 0x0121, 0x0123, 0x0125, 0x0127, 0x0129, 0x012b, 0x012d, 0x012f,
@@ -327,7 +327,7 @@ static chr lowerCharTable[] = {
  * Unicode: uppercase characters.
  */
 
-static crange upperRangeTable[] = {
+static const crange upperRangeTable[] = {
     {0x0041, 0x005a}, {0x00c0, 0x00d6}, {0x00d8, 0x00de}, {0x0189, 0x018b},
     {0x018e, 0x0191}, {0x0196, 0x0198}, {0x01b1, 0x01b3}, {0x01f6, 0x01f8},
     {0x0388, 0x038a}, {0x0391, 0x03a1}, {0x03a3, 0x03ab}, {0x03d2, 0x03d4},
@@ -340,7 +340,7 @@ static crange upperRangeTable[] = {
 
 #define NUM_UPPER_RANGE (sizeof(upperRangeTable)/sizeof(crange))
 
-static chr upperCharTable[] = {
+static const chr upperCharTable[] = {
     0x0100, 0x0102, 0x0104, 0x0106, 0x0108, 0x010a, 0x010c, 0x010e, 0x0110,
     0x0112, 0x0114, 0x0116, 0x0118, 0x011a, 0x011c, 0x011e, 0x0120, 0x0122,
     0x0124, 0x0126, 0x0128, 0x012a, 0x012c, 0x012e, 0x0130, 0x0132, 0x0134,
@@ -389,7 +389,7 @@ static chr upperCharTable[] = {
  * Unicode: unicode print characters excluding space.
  */
 
-static crange graphRangeTable[] = {
+static const crange graphRangeTable[] = {
     {0x0021, 0x007e}, {0x00a0, 0x011f}, {0x0121, 0x021f}, {0x0222, 0x0233},
     {0x0250, 0x02ad}, {0x02b0, 0x02ee}, {0x0300, 0x031f}, {0x0321, 0x034e},
     {0x0360, 0x0362}, {0x0384, 0x038a}, {0x038e, 0x03a1}, {0x03a3, 0x03ce},
@@ -511,7 +511,7 @@ static crange graphRangeTable[] = {
 
 #define NUM_GRAPH_RANGE (sizeof(graphRangeTable)/sizeof(crange))
 
-static chr graphCharTable[] = {
+static const chr graphCharTable[] = {
     0x0374, 0x0375, 0x037a, 0x037e, 0x038c, 0x0488, 0x0489, 0x04c7, 0x04c8,
     0x04cb, 0x04cc, 0x04f8, 0x04f9, 0x0589, 0x058a, 0x060c, 0x061b, 0x061f,
     0x098f, 0x0990, 0x09b2, 0x09bc, 0x09c7, 0x09c8, 0x09d7, 0x09dc, 0x09dd,
@@ -535,7 +535,7 @@ static chr graphCharTable[] = {
  * L*), Numbers (N*), Punctuation (P*), Symbols (S*) and Spaces (Zs).
  */
 
-static crange printRangeTable[] = {
+static const crange printRangeTable[] = {
     {0x0020, 0x007E}, {0x00A0, 0x01F5}, {0x01FA, 0x0217}, {0x0250, 0x02A8},
     {0x02B0, 0x02DE}, {0x02E0, 0x02E9}, {0x0374, 0x0375}, {0x0384, 0x038A},
     {0x038E, 0x03A1}, {0x03A3, 0x03CE}, {0x03D0, 0x03D6}, {0x03E2, 0x03F3},
@@ -593,7 +593,7 @@ static crange printRangeTable[] = {
 
 #define NUM_PRINT_RANGE (sizeof(printRangeTable)/sizeof(crange))
 
-static chr printCharTable[] = {
+static const chr printCharTable[] = {
     0x037A, 0x037E, 0x038C, 0x03DA, 0x03DC, 0x03DE, 0x03E0, 0x0589, 0x05BE,
     0x05C0, 0x05C3, 0x060C, 0x061B, 0x061F, 0x06E9, 0x093D, 0x0950, 0x09B2,
     0x0A5E, 0x0A8D, 0x0ABD, 0x0AD0, 0x0AE0, 0x0B3D, 0x0B9C, 0x0CDE, 0x0E01,
@@ -649,15 +649,15 @@ allmcces(
 
 /*
  - element - map collating-element name to celt
- ^ static celt element(struct vars *, chr *, chr *);
+ ^ static celt element(struct vars *, const chr *, const chr *);
  */
 static celt
 element(
     struct vars *v,		/* context */
-    chr *startp,		/* points to start of name */
-    chr *endp)			/* points just past end of name */
+    const chr *startp,		/* points to start of name */
+    const chr *endp)		/* points just past end of name */
 {
-    struct cname *cn;
+    const struct cname *cn;
     size_t len;
     Tcl_DString ds;
     const char *np;
@@ -818,13 +818,13 @@ eclass(
 /*
  - cclass - supply cvec for a character class
  * Must include case counterparts on request.
- ^ static struct cvec *cclass(struct vars *, chr *, chr *, int);
+ ^ static struct cvec *cclass(struct vars *, const chr *, const chr *, int);
  */
 static struct cvec *
 cclass(
     struct vars *v,		/* context */
-    chr *startp,		/* where the name starts */
-    chr *endp,			/* just past the end of the name */
+    const chr *startp,		/* where the name starts */
+    const chr *endp,		/* just past the end of the name */
     int cases)			/* case-independent? */
 {
     size_t len;
diff --git a/generic/regcomp.c b/generic/regcomp.c
index d228879..4137caf 100644
--- a/generic/regcomp.c
+++ b/generic/regcomp.c
@@ -52,7 +52,7 @@ static VOID repeat(struct vars *, struct state *, struct state *, int, int);
 static VOID bracket(struct vars *, struct state *, struct state *);
 static VOID cbracket(struct vars *, struct state *, struct state *);
 static VOID brackpart(struct vars *, struct state *, struct state *);
-static chr *scanplain(struct vars *);
+static const chr *scanplain(struct vars *);
 static VOID leaders(struct vars *, struct cvec *);
 static VOID onechr(struct vars *, pchr, struct state *, struct state *);
 static VOID dovec(struct vars *, struct cvec *, struct state *, struct state *);
@@ -79,7 +79,7 @@ static const char *stid(struct subre *, char *, size_t);
 /* === regc_lex.c === */
 static VOID lexstart(struct vars *);
 static VOID prefixes(struct vars *);
-static VOID lexnest(struct vars *, chr *, chr *);
+static VOID lexnest(struct vars *, const chr *, const chr *);
 static VOID lexword(struct vars *);
 static int next(struct vars *);
 static int lexescape(struct vars *);
@@ -88,9 +88,9 @@ static int brenext(struct vars *, pchr);
 static VOID skip(struct vars *);
 static chr newline(NOPARMS);
 #ifdef REG_DEBUG
-static chr *ch(NOPARMS);
+static const chr *ch(NOPARMS);
 #endif
-static chr chrnamed(struct vars *, chr *, chr *, pchr);
+static chr chrnamed(struct vars *, const chr *, const chr *, pchr);
 /* === regc_color.c === */
 static VOID initcm(struct vars *, struct colormap *);
 static VOID freecm(struct colormap *);
@@ -176,7 +176,7 @@ static struct cvec *clearcvec(struct cvec *);
 static VOID addchr(struct cvec *, pchr);
 static VOID addrange(struct cvec *, pchr, pchr);
 #ifdef REGEXP_MCCE_ENABLED
-static VOID addmcce(struct cvec *, chr *, chr *);
+static VOID addmcce(struct cvec *, const chr *, const chr *);
 #endif
 static int haschr(struct cvec *, pchr);
 static struct cvec *getcvec(struct vars *, int, int, int);
@@ -185,11 +185,11 @@ static VOID freecvec(struct cvec *);
 static int nmcces(struct vars *);
 static int nleaders(struct vars *);
 static struct cvec *allmcces(struct vars *, struct cvec *);
-static celt element(struct vars *, chr *, chr *);
+static celt element(struct vars *, const chr *, const chr *);
 static struct cvec *range(struct vars *, celt, celt, int);
 static int before(celt, celt);
 static struct cvec *eclass(struct vars *, celt, int);
-static struct cvec *cclass(struct vars *, chr *, chr *, int);
+static struct cvec *cclass(struct vars *, const chr *, const chr *, int);
 static struct cvec *allcases(struct vars *, pchr);
 static int cmp(const chr *, const chr *, size_t);
 static int casecmp(const chr *, const chr *, size_t);
@@ -199,10 +199,10 @@ static int casecmp(const chr *, const chr *, size_t);
 /* internal variables, bundled for easy passing around */
 struct vars {
     regex_t *re;
-    chr *now;			/* scan pointer into string */
-    chr *stop;			/* end of string */
-    chr *savenow;		/* saved now and stop for "subroutine call" */
-    chr *savestop;
+    const chr *now;		/* scan pointer into string */
+    const chr *stop;		/* end of string */
+    const chr *savenow;		/* saved now and stop for "subroutine call" */
+    const chr *savestop;
     int err;			/* error code (0 if none) */
     int cflags;			/* copy of compile flags */
     int lasttype;		/* type of previous token */
@@ -316,7 +316,7 @@ compile(
      */
 
     v->re = re;
-    v->now = (chr *)string;
+    v->now = string;
     v->stop = v->now + len;
     v->savenow = v->savestop = NULL;
     v->err = 0;
@@ -374,7 +374,7 @@ compile(
 	leaders(v, v->mcces);
 #ifdef REGEXP_MCCE_ENABLED
 	/* Function does nothing with NULL pointers */
-	addmcce(v->mcces, (chr *)NULL, (chr *)NULL);	/* dummy */
+	addmcce(v->mcces, (const chr *)NULL, (const chr *)NULL); /* dummy */
 #endif
     }
     CNOERR();
@@ -1475,7 +1475,7 @@ cbracket(
     struct arc *ba;			/* arc from left, from bracket() */
     struct arc *pa;			/* MCCE-prototype arc */
     color co;
-    chr *p;
+    const chr *p;
     int i;
 
     NOERR();
@@ -1564,8 +1564,8 @@ brackpart(
     celt startc;
     celt endc;
     struct cvec *cv;
-    chr *startp;
-    chr *endp;
+    const chr *startp;
+    const chr *endp;
     chr c[1];
 
     /*
@@ -1672,13 +1672,13 @@ brackpart(
  - scanplain - scan PLAIN contents of [. etc.
  * Certain bits of trickery in lex.c know that this code does not try to look
  * past the final bracket of the [. etc.
- ^ static chr *scanplain(struct vars *);
+ ^ static const chr *scanplain(struct vars *);
  */
-static chr *			/* just after end of sequence */
+static const chr *		/* just after end of sequence */
 scanplain(
     struct vars *v)
 {
-    chr *endp;
+    const chr *endp;
 
     assert(SEE(COLLEL) || SEE(ECLASS) || SEE(CCLASS));
     NEXT();
@@ -1707,7 +1707,7 @@ leaders(
     struct cvec *cv)
 {
     int mcce;
-    chr *p;
+    const chr *p;
     chr leader;
     struct state *s;
     struct arc *a;
@@ -1773,9 +1773,9 @@ dovec(
     struct state *rp)
 {
     chr ch, from, to;
-    chr *p;
+    const chr *p;
     int i;
-    
+
     for (p = cv->chrs, i = cv->nchrs; i > 0; p++, i--) {
 	ch = *p;
 	newarc(v->nfa, PLAIN, subcolor(v->cm, ch), lp, rp);
@@ -1800,7 +1800,7 @@ dovec(
 {
     chr ch, from, to;
     celt ce;
-    chr *p;
+    const chr *p;
     int i;
     struct cvec *leads;
     color co;
@@ -1949,7 +1949,7 @@ nextleader(
     pchr to)
 {
     int i;
-    chr *p;
+    const chr *p;
     chr ch;
     celt it = NOCELT;