From c8fb255fde88c6d2b08dd01f623d95e85ef96d1d Mon Sep 17 00:00:00 2001
From: Colomban Wendling <ban@herbesfolles.org>
Date: Thu, 25 May 2023 23:26:06 +0200
Subject: [PATCH] Fix calls to ctype functions

All ctype functions like `isdigit()` and alike expect a character as an
`unsigned char` or EOF, anything else has undefined behavior.

This commit should fix all calls to the various ctype functions either:

* adding `unsigned char` cast where appropriate;
* removing useless `int` casts that are more confusing than useful.

Some instances required slightly more involved changes though, but the
fix itself is the same.

To find the calls to check, I used an equivalent to the following:

```
git grep -P 'is(alnum|alpha|cntrl|x?digit|graph|lower|print|punct|'\
'space|upper|ascii|blank)|to(low|up)er'
```

...and then proceeded to manually check them to see if the call, or
call chain, was using appropriate values and types.
---
 readtags.c | 39 +++++++++++++++++++++------------------
 1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/readtags.c b/readtags.c
index 25c05d31..45488c36 100644
--- a/readtags.c
+++ b/readtags.c
@@ -135,7 +135,7 @@ static int readtags_fseek(FILE *fp, rt_off_t pos, int whence)
 }
 
 /* Converts a hexadecimal digit to its value */
-static int xdigitValue (char digit)
+static int xdigitValue (unsigned char digit)
 {
 	if (digit >= '0' && digit <= '9')
 		return digit - '0';
@@ -151,32 +151,33 @@ static int xdigitValue (char digit)
  * Reads the first character from the string, possibly un-escaping it, and
  * advances *s to the start of the next character.
  */
-static int readTagCharacter (const char **s)
+static int readTagCharacter (const char **const s)
 {
-	int c = **(const unsigned char **)s;
+	const unsigned char *p = (const unsigned char *) *s;
+	int c = *p;
 
-	(*s)++;
+	p++;
 
 	if (c == '\\')
 	{
-		switch (**s)
+		switch (*p)
 		{
-			case 't': c = '\t'; (*s)++; break;
-			case 'r': c = '\r'; (*s)++; break;
-			case 'n': c = '\n'; (*s)++; break;
-			case '\\': c = '\\'; (*s)++; break;
+			case 't': c = '\t'; p++; break;
+			case 'r': c = '\r'; p++; break;
+			case 'n': c = '\n'; p++; break;
+			case '\\': c = '\\'; p++; break;
 			/* Universal-CTags extensions */
-			case 'a': c = '\a'; (*s)++; break;
-			case 'b': c = '\b'; (*s)++; break;
-			case 'v': c = '\v'; (*s)++; break;
-			case 'f': c = '\f'; (*s)++; break;
+			case 'a': c = '\a'; p++; break;
+			case 'b': c = '\b'; p++; break;
+			case 'v': c = '\v'; p++; break;
+			case 'f': c = '\f'; p++; break;
 			case 'x':
-				if (isxdigit ((*s)[1]) && isxdigit ((*s)[2]))
+				if (isxdigit (p[1]) && isxdigit (p[2]))
 				{
-					int val = (xdigitValue ((*s)[1]) << 4) | xdigitValue ((*s)[2]);
+					int val = (xdigitValue (p[1]) << 4) | xdigitValue (p[2]);
 					if (val < 0x80)
 					{
-						(*s) += 3;
+						p += 3;
 						c = val;
 					}
 				}
@@ -184,6 +185,8 @@ static int readTagCharacter (const char **s)
 		}
 	}
 
+	*s = (const char *) p;
+
 	return c;
 }
 
@@ -610,12 +613,12 @@ static tagResult parseTagLine (tagFile *file, tagEntry *const entry, int *err)
 				else
 					++p;
 			}
-			else if (isdigit ((int) *(unsigned char*) p))
+			else if (isdigit (*(unsigned char*) p))
 			{
 				/* parse line number */
 				entry->address.pattern = p;
 				entry->address.lineNumber = atol (p);
-				while (isdigit ((int) *(unsigned char*) p))
+				while (isdigit (*(unsigned char*) p))
 					++p;
 				if (p)
 				{