aztec: avoid possible overflow in comparison

output/CLI/testcommon: suppress some gcc-16 (C23) warnings
  "-Wdiscarded-qualifiers" (QChar)
GUI: suppress some gcc-16 (C23) warnings
  "-Wdeprecated-enum-enum-conversion"
channel: use explicit `const struct` for precalcs instead of
  typedef (makes code more transparent)
README.linux: Fedora 43 -> 44

README.linux

@@ -1,6 +1,6 @@
-% README.linux 2026-01-01
+% README.linux 2026-05-15
 % Tested on Ubuntu 20.04.4 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS and
-% Fedora Linux 43 (Workstation Edition)
+% Fedora Linux 44 (Workstation Edition)
 % vim: set ts=4 sw=4 et :
 
 1. Prerequisites for building zint

backend/aztec.c

@@ -497,7 +497,7 @@ static int az_tokens_add_chk(struct az_state *state, const int extra) {
         }
         state->tokens.size = size;
         state->tokens.used = 0;
-    } else if (state->tokens.used + extra >= state->tokens.size) {
+    } else if (state->tokens.used >= state->tokens.size - extra) { /* Compare this way to avoid possible overflow */
         struct az_token *tokens;
         const unsigned short size = state->tokens.size * 2;
         if (size <= state->tokens.size /* Overflow */
@@ -1029,7 +1029,7 @@ static int az_binary_string(const unsigned char source[], const int length, int
     }
 
     for (i = 0; i < stateEnd.tokens.used; i++) {
-        const struct az_token *token = stateEnd.tokens.tokens + i;
+        const struct az_token *const token = stateEnd.tokens.tokens + i;
         const int count = token->count;
         if (count < 0) {
             bp = z_bin_append_posn(token->value, -count, binary_string, bp);

backend/channel.c

@@ -35,9 +35,9 @@
 #include <stdio.h>
 #include "common.h"
 
-typedef const struct s_channel_precalc {
+struct channel_precalc {
     int value; unsigned char B[8]; unsigned char S[8]; unsigned char bmax[7]; unsigned char smax[7];
-} channel_precalc;
+};
 
 #if 0
 #define CHANNEL_GENERATE_PRECALCS
@@ -49,8 +49,8 @@ typedef const struct s_channel_precalc {
 static void channel_generate_precalc(int channels, int value, int mod, int last, int B[8], int S[8], int bmax[7],
             int smax[7]) {
     int i;
-    if (value == mod) printf("static channel_precalc channel_precalcs%d[] = {\n", channels);
+    if (value == mod) printf("static const struct channel_precalc channel_precalcs%d[] = {\n", channels);
-    printf("    { %7ld, {", value); for (i = 0; i < 8; i++) printf(" %d,", B[i]); fputs(" },", stdout);
+    printf("    { %7d, {", value); for (i = 0; i < 8; i++) printf(" %d,", B[i]); fputs(" },", stdout);
     fputs(" {", stdout); for (i = 0; i < 8; i++) printf(" %d,", S[i]); fputs(" },", stdout);
     fputs(" {", stdout); for (i = 0; i < 7; i++) printf(" %d,", bmax[i]); fputs(" },", stdout);
     fputs(" {", stdout); for (i = 0; i < 7; i++) printf(" %d,", smax[i]); fputs(" }, },\n", stdout);
@@ -60,7 +60,8 @@ static void channel_generate_precalc(int channels, int value, int mod, int last,
 #include "channel_precalcs.h"
 #endif
 
-static int channel_copy_precalc(channel_precalc *const precalc, int B[8], int S[8], int bmax[7], int smax[7]) {
+static int channel_copy_precalc(const struct channel_precalc *const precalc, int B[8], int S[8], int bmax[7],
+            int smax[7]) {
     int i;
 
     for (i = 0; i < 7; i++) {
@@ -89,7 +90,7 @@ static void CHNCHR(int channels, int target_value, int B[8], int S[8]) {
     /* Use of initial pre-calculations taken from Barcode Writer in Pure PostScript (BWIPP)
        Copyright (c) 2004-2026 Terry Burton */
     /* SPDX-License-Identifier: MIT */
-    static channel_precalc initial_precalcs[6] = {
+    static const struct channel_precalc initial_precalcs[6] = {
         { 0, { 1, 1, 1, 1, 1, 2, 1, 2, }, { 1, 1, 1, 1, 1, 1, 1, 3, }, { 1, 1, 1, 1, 1, 3, 2, },
             { 1, 1, 1, 1, 1, 3, 3, }, },
         { 0, { 1, 1, 1, 1, 2, 1, 1, 3, }, { 1, 1, 1, 1, 1, 1, 1, 4, }, { 1, 1, 1, 1, 4, 3, 3, },

backend/channel_precalcs.h

@@ -1,6 +1,6 @@
 /*
     libzint - the open source barcode library
-    Copyright (C) 2020-2022 Robin Stuart <rstuart114@gmail.com>
+    Copyright (C) 2020-2026 Robin Stuart <rstuart114@gmail.com>
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
@@ -35,13 +35,13 @@
 /* Channel code precalculated values to avoid excessive looping */
 /* To generate uncomment CHANNEL_GENERATE_PRECALCS define and run "backend/tests/test_channel -f generate -g" */
 /* Paste result below here */
-static channel_precalc channel_precalcs7[] = {
+static const struct channel_precalc channel_precalcs7[] = {
     {  115338, { 1, 3, 1, 1, 1, 1, 5, 1, }, { 1, 1, 1, 2, 1, 2, 3, 3, }, { 1, 7, 5, 5, 5, 5, 5, }, { 1, 7, 7, 7, 6, 6, 5, }, },
     {  230676, { 1, 1, 2, 2, 4, 1, 1, 2, }, { 1, 2, 1, 3, 2, 1, 3, 1, }, { 1, 7, 7, 6, 5, 2, 2, }, { 1, 7, 6, 6, 4, 3, 3, }, },
     {  346014, { 1, 2, 3, 1, 1, 1, 3, 2, }, { 1, 2, 2, 1, 1, 3, 1, 3, }, { 1, 7, 6, 4, 4, 4, 4, }, { 1, 7, 6, 5, 5, 5, 3, }, },
     {  461352, { 1, 2, 1, 1, 1, 2, 2, 4, }, { 1, 3, 1, 1, 3, 2, 2, 1, }, { 1, 7, 6, 6, 6, 6, 5, }, { 1, 7, 5, 5, 5, 3, 2, }, },
 };
-static channel_precalc channel_precalcs8[] = {
+static const struct channel_precalc channel_precalcs8[] = {
     {  119121, { 2, 1, 3, 2, 1, 3, 2, 1, }, { 1, 1, 1, 4, 3, 2, 1, 2, }, { 8, 7, 7, 5, 4, 4, 2, }, { 8, 8, 8, 8, 5, 3, 2, }, },
     {  238242, { 2, 1, 1, 2, 2, 2, 1, 4, }, { 1, 1, 3, 1, 1, 2, 4, 2, }, { 8, 7, 7, 7, 6, 5, 4, }, { 8, 8, 8, 6, 6, 6, 5, }, },
     {  357363, { 2, 2, 1, 4, 1, 1, 1, 3, }, { 1, 1, 1, 1, 3, 2, 5, 1, }, { 8, 7, 6, 6, 3, 3, 3, }, { 8, 8, 8, 8, 8, 6, 5, }, },

backend/output.c

@@ -957,7 +957,7 @@ static int out_maybe_mkdir(const char *path) {
 }
 
 /* Create output file, creating sub-directories if necessary. Returns `fopen()` FILE pointer */
-INTERNAL FILE *zint_out_fopen(const char filename[256], const char *mode) {
+INTERNAL FILE *zint_out_fopen(char filename[256], const char *mode) {
     FILE *outfile;
 
 #ifdef _WIN32
@@ -968,12 +968,10 @@ INTERNAL FILE *zint_out_fopen(const char filename[256], const char *mode) {
         char dirname[256];
         char *d;
 #ifdef _WIN32
-        char *dirend = strrchr(filename, '\\');
+        char *const dirend_backslash = strrchr(filename, '\\');
-        if (!dirend) {
+        char *const dirend = dirend_backslash ? dirend_backslash : strrchr(filename, '/');
-            dirend = strrchr(filename, '/');
-        }
 #else
-        char *dirend = strrchr(filename, '/');
+        char *const dirend = strrchr(filename, '/');
 #endif
         if (!dirend) {
             return outfile;

backend/output.h

@@ -71,7 +71,7 @@ INTERNAL float zint_out_large_bar_height(struct zint_symbol *symbol, const int s
                 int *symbol_height_si);
 
 /* Create output file, creating sub-directories if necessary. Returns `fopen()` FILE pointer */
-INTERNAL FILE *zint_out_fopen(const char filename[256], const char *mode);
+INTERNAL FILE *zint_out_fopen(char filename[256], const char *mode);
 
 #ifdef _WIN32
 /* Do `fopen()` on Windows, assuming `filename` is UTF-8 encoded. Props Marcel, ticket #288 */

backend/tests/testcommon.c

@@ -2163,7 +2163,8 @@ int testUtilHaveLibreOffice(void) {
 int testUtilVerifyLibreOffice(const char *filename, int debug) {
     char cmd[512 + 128];
     char svg[512];
-    char *slash, *dot;
+    const char *slash;
+    char *dot;
     char buf[16384];
     char *b = buf, *be = buf + sizeof(buf) - 1;
     FILE *fp;
@@ -4347,7 +4348,7 @@ static int textUtilZXingCPPDX(const char *expected, const int expected_len, cons
 
 /* Helper to append add-on if any to EAN-13, returning expected length */
 static int textUtilZXingCPPEAN13AddOn(const char *expected, const int expected_len, char *out) {
-    char *sep;
+    const char *sep;
     if ((sep = strchr(expected, '+')) != NULL || (sep = strchr(expected, ' ')) != NULL) {
         const int addon_len = expected_len - (int) (sep + 1 - expected);
         if (addon_len <= 2) {

frontend/main.c

@@ -736,8 +736,8 @@ static int supported_filetype(const char *const filetype, const int no_png, int
 }
 
 /* Get file extension, excluding those of more than 4 letters */
-static char *get_extension(const char *const file) {
+static const char *get_extension(const char *const file) {
-    char *const dot = strrchr(file, '.');
+    const char *const dot = strrchr(file, '.');
     if (dot && strlen(file) - (dot - file) <= 5) { /* Only recognize up to 4 letter extensions */
         return dot + 1;
     }
@@ -755,7 +755,7 @@ static void set_extension(char file[256], const char *const filetype) {
     cpy_str(lc_filetype, ARRAY_SIZE(lc_filetype), filetype);
     to_lower(lc_filetype);
 
-    extension = get_extension(file);
+    extension = (char *) get_extension(file);
     if (extension) {
         cpy_str(lc_extension, ARRAY_SIZE(lc_extension), extension);
         to_lower(lc_extension);
@@ -1517,7 +1517,7 @@ int main(int argc, char **argv) {
     int val;
     int i;
     int ret;
-    char *outfile_extension;
+    const char *outfile_extension;
     int data_arg_num = 0;
     int seg_count = 0;
     float x_dim_mm = 0.0f, dpmm = 0.0f;

frontend_qt/mainwindow.cpp

@@ -60,19 +60,22 @@
 
 static const int tempMessageTimeout = 2000;
 
+// Suppress gcc-16 (C23) warning -Wdeprecated-enum-enum-conversion
+#define QKC(M, K)   (int(M) | int(K))
+
 // Use on Windows also (i.e. not using QKeySequence::Quit)
-Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, quitKeySeq, (Qt::CTRL | Qt::Key_Q))
+Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, quitKeySeq, QKC(Qt::CTRL, Qt::Key_Q))
 
-Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, openCLISeq, (Qt::SHIFT | Qt::CTRL | Qt::Key_C))
+Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, openCLISeq, QKC(Qt::SHIFT | Qt::CTRL, Qt::Key_C))
 
-Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, copyBMPSeq, (Qt::SHIFT | Qt::CTRL | Qt::Key_B))
+Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, copyBMPSeq, QKC(Qt::SHIFT | Qt::CTRL, Qt::Key_B))
-Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, copyEMFSeq, (Qt::SHIFT | Qt::CTRL | Qt::Key_E))
+Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, copyEMFSeq, QKC(Qt::SHIFT | Qt::CTRL, Qt::Key_E))
-Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, copyGIFSeq, (Qt::SHIFT | Qt::CTRL | Qt::Key_G))
+Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, copyGIFSeq, QKC(Qt::SHIFT | Qt::CTRL, Qt::Key_G))
-Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, copyPNGSeq, (Qt::SHIFT | Qt::CTRL | Qt::Key_P))
+Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, copyPNGSeq, QKC(Qt::SHIFT | Qt::CTRL, Qt::Key_P))
-Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, copySVGSeq, (Qt::SHIFT | Qt::CTRL | Qt::Key_S))
+Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, copySVGSeq, QKC(Qt::SHIFT | Qt::CTRL, Qt::Key_S))
-Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, copyTIFSeq, (Qt::SHIFT | Qt::CTRL | Qt::Key_T))
+Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, copyTIFSeq, QKC(Qt::SHIFT | Qt::CTRL, Qt::Key_T))
 
-Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, factoryResetSeq, (Qt::SHIFT | Qt::CTRL | Qt::Key_R))
+Q_GLOBAL_STATIC_WITH_ARGS(QKeySequence, factoryResetSeq, QKC(Qt::SHIFT | Qt::CTRL, Qt::Key_R))
 
 // RGB hexadecimal 6 or 8 in length or CMYK comma-separated decimal percentages "C,M,Y,K"
 static const QString colorREstr(QSL("^([0-9A-Fa-f]{6}([0-9A-Fa-f]{2})?)|(((100|[0-9]{0,2}),){3}(100|[0-9]{0,2}))$"));