lib/atoi/a2i.[ch]: Add const-generic macros

These overloaded macros allow passing either a const or a non-const
endp, and will call the appropriate function.  This kind of const
overloading has prior art in C23's string functions, such as memchr(3).

Martin suggested using an artificial function pointer in _Generic(3); it
allows switching on various types at the same time.

Also add a comment referring to liba2i's PDF manual for documentation.

Link: <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3096.pdf#subsubsection.7.26.5.2>
Link: <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114731>
Link: <http:https://www.alejandro-colomar.es/share/dist/liba2i/git/HEAD/liba2i-HEAD.pdf>
Co-developed-by: Martin Uecker <[email protected]>
Signed-off-by: Alejandro Colomar <[email protected]>

lib/atoi/a2i.c

@@ -7,20 +7,40 @@
 #include "atoi/a2i.h"
 
 
-extern inline int a2sh(short *restrict n, const char *s,
+extern inline int a2sh_c(short *restrict n, const char *s,
+ const char **restrict endp, int base, short min, short max);
+extern inline int a2si_c(int *restrict n, const char *s,
+ const char **restrict endp, int base, int min, int max);
+extern inline int a2sl_c(long *restrict n, const char *s,
+ const char **restrict endp, int base, long min, long max);
+extern inline int a2sll_c(long long *restrict n, const char *s,
+ const char **restrict endp, int base, long long min, long long max);
+extern inline int a2uh_c(unsigned short *restrict n, const char *s,
+ const char **restrict endp, int base, unsigned short min,
+ unsigned short max);
+extern inline int a2ui_c(unsigned int *restrict n, const char *s,
+ const char **restrict endp, int base, unsigned int min, unsigned int max);
+extern inline int a2ul_c(unsigned long *restrict n, const char *s,
+ const char **restrict endp, int base, unsigned long min, unsigned long max);
+extern inline int a2ull_c(unsigned long long *restrict n, const char *s,
+ const char **restrict endp, int base, unsigned long long min,
+ unsigned long long max);
+
+
+extern inline int a2sh_nc(short *restrict n, char *s,
  char **restrict endp, int base, short min, short max);
-extern inline int a2si(int *restrict n, const char *s,
+extern inline int a2si_nc(int *restrict n, char *s,
  char **restrict endp, int base, int min, int max);
-extern inline int a2sl(long *restrict n, const char *s,
+extern inline int a2sl_nc(long *restrict n, char *s,
  char **restrict endp, int base, long min, long max);
-extern inline int a2sll(long long *restrict n, const char *s,
+extern inline int a2sll_nc(long long *restrict n, char *s,
  char **restrict endp, int base, long long min, long long max);
-extern inline int a2uh(unsigned short *restrict n, const char *s,
+extern inline int a2uh_nc(unsigned short *restrict n, char *s,
  char **restrict endp, int base, unsigned short min, unsigned short max);
-extern inline int a2ui(unsigned int *restrict n, const char *s,
+extern inline int a2ui_nc(unsigned int *restrict n, char *s,
  char **restrict endp, int base, unsigned int min, unsigned int max);
-extern inline int a2ul(unsigned long *restrict n, const char *s,
+extern inline int a2ul_nc(unsigned long *restrict n, char *s,
  char **restrict endp, int base, unsigned long min, unsigned long max);
-extern inline int a2ull(unsigned long long *restrict n, const char *s,
+extern inline int a2ull_nc(unsigned long long *restrict n, char *s,
  char **restrict endp, int base, unsigned long long min,
  unsigned long long max);