From 6c9fa195b08a24ca759c7d0e2129a33137bbbccd Mon Sep 17 00:00:00 2001
From: "jan.nijtmans" <nijtmans@users.sourceforge.net>
Date: Wed, 6 May 2020 13:03:29 +0000
Subject: Change Invalid() parameter type to "const char *".  Also call
 Invalid() first in Tcl_UtfNext(), so if src[1] is invalid src[2] doesn't need
 to be checked any more.

Note: This order change, calling Invalid() first was wrong, and is corrected in later commits. Thanks, Don, for noticing this!
---
 generic/tclUtf.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/generic/tclUtf.c b/generic/tclUtf.c
index 528d5de..60e475a 100644
--- a/generic/tclUtf.c
+++ b/generic/tclUtf.c
@@ -81,7 +81,7 @@ static CONST unsigned char totalBytes[256] = {
  */
 
 static int		UtfCount(int ch);
-static int		Invalid(unsigned char *src);
+static int		Invalid(const char *src);
 
 /*
  *---------------------------------------------------------------------------
@@ -154,9 +154,9 @@ static CONST unsigned char bounds[28] = {
 
 INLINE static int
 Invalid(
-    unsigned char *src)	/* Points to lead byte of a UTF-8 byte sequence */
+    const char *src)	/* Points to lead byte of a UTF-8 byte sequence */
 {
-    unsigned char byte = *src;
+    unsigned char byte = UCHAR(*src);
     int index;
 
     if ((byte & 0xC3) != 0xC0) {
@@ -164,7 +164,7 @@ Invalid(
 	return 0;
     }
     index = (byte - 0xC0) >> 1;
-    if (src[1] < bounds[index] || src[1] > bounds[index+1]) {
+    if (UCHAR(src[1]) < bounds[index] || UCHAR(src[1]) > bounds[index+1]) {
 	/* Out of bounds - report invalid. */
 	return 1;
     }
@@ -648,9 +648,14 @@ CONST char *
 Tcl_UtfNext(
     CONST char *src)		/* The current location in the string. */
 {
-    int left = totalBytes[UCHAR(*src)];
-    const char *next = src + 1;
+    int left;
+    const char *next;
 
+    if (Invalid(src)) {
+	return src + 1;
+    }
+    left = totalBytes[UCHAR(*src)];
+    next = src + 1;
     while (--left) {
 	if ((*next & 0xC0) != 0x80) {
 	    /*
@@ -662,9 +667,6 @@ Tcl_UtfNext(
 	}
 	next++;
     }
-    if (Invalid((unsigned char *)src)) {
-	return src + 1;
-    }
     return next;
 }
 
@@ -699,7 +701,7 @@ Tcl_UtfPrev(
 				/* If we cannot find a lead byte that might
 				 * start a prefix of a valid UTF byte sequence,
 				 * we will fallback to a one-byte back step */
-    unsigned char *look = (unsigned char *)fallback;
+    const char *look = fallback;
 				/* Start search at the fallback position */
 
     /* Quick boundary case exit. */
@@ -708,7 +710,7 @@ Tcl_UtfPrev(
     }
 
     do {
-	unsigned char byte = look[0];
+	unsigned char byte = UCHAR(look[0]);
 
 	if (byte < 0x80) {
 	    /*
-- 
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