stdckdint: add compatibility header

This only implements unsigned types for now, as there are no known use
cases for signed checked arithmetic as of yet. The macros will safely
error out at compilation time if signed types are misused.

compat/Makefile.am

@@ -1,4 +1,4 @@
-noinst_HEADERS = stdbit/stdbit.h
+noinst_HEADERS = stdbit/stdbit.h stdckdint/stdckdint.h
 pkglib_LTLIBRARIES = libcompat.la
 libcompat_la_SOURCES = dummy.c
 libcompat_la_LIBADD = $(LTLIBOBJS) $(LIBRT) $(LIBM)

compat/stdckdint/stdckdint.h

@@ -0,0 +1,66 @@
+/*
+ * Copyright (C) 2024 Rémi Denis-Courmont
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+ */
+
+#ifndef __STDC_VERSION_STDCKDINT_H__
+# define __STDC_VERSION_STDCKDINT_H__ 202311L
+
+# if defined(__GNUC__) || defined(__clang__)
+#  define ckd_add(r, a, b) __builtin_add_overflow(a, b, r)
+#  define ckd_sub(r, a, b) __builtin_sub_overflow(a, b, r)
+#  define ckd_mul(r, a, b) __builtin_mul_overflow(a, b, r)
+# else
+#  include <limits.h>
+
+#  define __ckd_unsigned(suffix, type, MAX) \
+static inline _Bool __ckd_add_##suffix(type *r, type a, type b) \
+{ \
+    *r = a + b; \
+    return ((type)(a + b)) < a; \
+} \
+\
+static inline _Bool __ckd_sub_##suffix(type *r, type a, type b) \
+{ \
+    *r = a - b; \
+    return a < b; \
+} \
+\
+static inline _Bool __ckd_mul_##suffix(type *r, type a, type b) \
+{ \
+    *r = a * b; \
+    return b > 0 && a > (MAX / b); \
+}
+
+#  define __ckd_func(op, r, a, b) \
+    _Generic (*(r), \
+        unsigned char:      __ckd_##op##_uc((unsigned char *)(r), a, b), \
+        unsigned short:     __ckd_##op##_us((unsigned short *)(r), a, b), \
+        unsigned int:       __ckd_##op##_ui((unsigned int *)(r), a, b), \
+        unsigned long:      __ckd_##op##_ul((unsigned long *)(r), a, b), \
+        unsigned long long: __ckd_##op##_ull((unsigned long long *)(r), a, b))
+
+__ckd_unsigned(uc,  unsigned char,      UCHAR_MAX)
+__ckd_unsigned(us,  unsigned short,     USHRT_MAX)
+__ckd_unsigned(ui,  unsigned int,       UINT_MAX)
+__ckd_unsigned(ul,  unsigned long,      ULONG_MAX)
+__ckd_unsigned(ull, unsigned long long, ULLONG_MAX)
+
+#  define ckd_add(r, a, b) __ckd_func(add, r, a, b)
+#  define ckd_sub(r, a, b) __ckd_func(sub, r, a, b)
+#  define ckd_mul(r, a, b) __ckd_func(mul, r, a, b)
+# endif
+#endif /* __STDC_VERSION_STDCKDINT_H__ */

configure.ac

@@ -983,6 +983,9 @@ dnl
 AC_CHECK_HEADER([stdbit.h],, [
   CPPFLAGS="${CPPFLAGS} -I\$(top_srcdir)/compat/stdbit"
 ])
+AC_CHECK_HEADER([stdckdint.h],, [
+  CPPFLAGS="${CPPFLAGS} -I\$(top_srcdir)/compat/stdckdint"
+])
 
 dnl  POSIX
 AC_CHECK_HEADERS([arpa/inet.h poll.h pthread.h search.h sys/shm.h sys/socket.h sys/uio.h wordexp.h])

meson.build

@@ -208,6 +208,7 @@ endif
 
 check_c_headers = [
     ['stdbit.h'],
+    ['stdckdint.h'],
     ['arpa/inet.h'],
     ['threads.h'],
     ['netinet/tcp.h'],
@@ -269,6 +270,9 @@ endforeach
 if not cdata.has('HAVE_STDBIT_H')
     list_inc_dirs += 'compat/stdbit'
 endif
+if not cdata.has('HAVE_STDCKDINT_H')
+    list_inc_dirs += 'compat/stdckdint'
+endif
 vlc_include_dirs = include_directories(list_inc_dirs)
 
 #