a2i(): Maximal minimalism #1372

alejandro-colomar · 2025-10-18T07:05:51Z

I've managed to find a way to implement a2i() in just a couple of simple macros; a short one for the body, one for massaging const, plus a one-liner for connecting both.

I need to test this in liba2i first. I'll keep as a draft here until I test it thoroughly. (Done.)

I've been trying to find a way to write it this simple for a looong time. Finally, I found it! :)

Edit: Testing in liba2i says all's good.

Revisions:

v2

Use const_cast() to do all the casts for discarding const.
Allow a no-op cast in const_cast(), for supporting QChar.

$ git range-diff shadow/master gh/funclit funclit 
-:  -------- > 1:  fccfefc7 lib/cast.h: const_cast(): Accept cast to same type
1:  bae69feb ! 2:  bbce57a2 lib/atoi/: a2i(): Re-implement with a statement expression
    @@ lib/atoi/a2i/a2i.h
     +
     +#include "atoi/strtoi/strtoi.h"
     +#include "atoi/strtoi/strtou_noneg.h"
    ++#include "cast.h"
      
      
      /*
    @@ lib/atoi/a2i/a2i.h
     +#define QChar_of(s)  typeof                                           \
     +(                                                                     \
     +  _Generic(s,                                                   \
    -+          const char *:  *(const char *) "",                    \
    -+          const void *:  *(const char *) "",                    \
    -+          char *:        *(char *) "",                          \
    -+          void *:        *(char *) ""                           \
    ++          const char *:  *const_cast(const char *, ""),         \
    ++          const void *:  *const_cast(const char *, ""),         \
    ++          char *:        *const_cast(char *,       ""),         \
    ++          void *:        *const_cast(char *,       "")          \
     +  )                                                             \
      )
      
    @@ lib/atoi/a2i/a2i.h
     +          unsigned int:       strtou_noneg,                     \
     +          unsigned long:      strtou_noneg,                     \
     +          unsigned long long: strtou_noneg                      \
    -+  )(s_, (char **) endp_, base_, min_, max_, &status);           \
    ++  )(s_, const_cast(char **, endp_), base_, min_, max_, &status);\
     +                                                                      \
     +  if (status != 0)                                              \
     +          errno = status;                                       \
2:  2cec086a = 3:  5ec018e3 lib/atoi/, */: Move all a2i() macros to the same file
3:  47c20df6 ! 4:  0520cdbb lib/atoi/, */: Move all str2i() macros together with a2i()
    @@ lib/atoi/a2i.h
      
      #include "atoi/strtoi/strtoi.h"
      #include "atoi/strtoi/strtou_noneg.h"
    + #include "cast.h"
     +#include "typetraits.h"

v3

Fix implementation of QChar_of(). A const_cast() doesn't work there. Use a compound literal instead, which is also simpler.
Revert changes to const_cast().

$ git range-diff shadow/master gh/funclit funclit 
1:  fccfefc7 < -:  -------- lib/cast.h: const_cast(): Accept cast to same type
2:  bbce57a2 ! 1:  ef203087 lib/atoi/: a2i(): Re-implement with a statement expression
    @@ lib/atoi/a2i/a2i.h
     +#define QChar_of(s)  typeof                                           \
     +(                                                                     \
     +  _Generic(s,                                                   \
    -+          const char *:  *const_cast(const char *, ""),         \
    -+          const void *:  *const_cast(const char *, ""),         \
    -+          char *:        *const_cast(char *,       ""),         \
    -+          void *:        *const_cast(char *,       "")          \
    ++          const char *:  (const char){0},                       \
    ++          const void *:  (const char){0},                       \
    ++          char *:        (char){0},                             \
    ++          void *:        (char){0}                              \
     +  )                                                             \
      )
      
3:  5ec018e3 = 2:  55f85cd3 lib/atoi/, */: Move all a2i() macros to the same file
4:  0520cdbb = 3:  b9dd4544 lib/atoi/, */: Move all str2i() macros together with a2i()

v3b

Use (T){1} instead of (T){0} for the dummy compound literals. 0 is more prone to accidents where pointers are mixed with integers, as 0 is a valid null pointer constant. 1 is not acceptable as a pointer, so it has stronger type safety. We don't care about the actual value, since we use it as input to typeof(), so 1 is fine.

$ git range-diff shadow/master gh/funclit funclit 
1:  ef203087 ! 1:  af6a5dd3 lib/atoi/: a2i(): Re-implement with a statement expression
    @@ lib/atoi/a2i/a2i.h
     +#define QChar_of(s)  typeof                                           \
     +(                                                                     \
     +  _Generic(s,                                                   \
    -+          const char *:  (const char){0},                       \
    -+          const void *:  (const char){0},                       \
    -+          char *:        (char){0},                             \
    -+          void *:        (char){0}                              \
    ++          const char *:  (const char){1},                       \
    ++          const void *:  (const char){1},                       \
    ++          char *:        (char){1},                             \
    ++          void *:        (char){1}                              \
     +  )                                                             \
      )
      
2:  55f85cd3 = 2:  159a38ed lib/atoi/, */: Move all a2i() macros to the same file
3:  b9dd4544 = 3:  983e2440 lib/atoi/, */: Move all str2i() macros together with a2i()

v4

Remove local variables that are not necessary. s and base are only used once, and can have a fixed type, so we don't need the locals.

$ git range-diff shadow/master gh/funclit funclit 
1:  af6a5dd3 ! 1:  6cbdc9e8 lib/atoi/: a2i(): Re-implement with a statement expression
    @@ lib/atoi/a2i/a2i.h
     +#define a2i_(T, QChar, n, s, endp, base, min, max)                    \
     +({                                                                    \
     +  T      *n_ = n;                                               \
    -+  QChar  *s_ = s;                                               \
     +  QChar  **endp_ = endp;                                        \
    -+  int    base_ = base;                                          \
     +  T      min_ = min;                                            \
     +  T      max_ = max;                                            \
     +                                                                      \
    @@ lib/atoi/a2i/a2i.h
     +          unsigned int:       strtou_noneg,                     \
     +          unsigned long:      strtou_noneg,                     \
     +          unsigned long long: strtou_noneg                      \
    -+  )(s_, const_cast(char **, endp_), base_, min_, max_, &status);\
    ++  )(s, const_cast(char **, endp_), base, min_, max_, &status);  \
     +                                                                      \
     +  if (status != 0)                                              \
     +          errno = status;                                       \
2:  159a38ed = 2:  dc464daa lib/atoi/, */: Move all a2i() macros to the same file
3:  983e2440 = 3:  d54ca4f1 lib/atoi/, */: Move all str2i() macros together with a2i()

v4b

Rebase

$ git rd 
1:  6cbdc9e8 = 1:  9f7f1574 lib/atoi/: a2i(): Re-implement with a statement expression
2:  dc464daa = 2:  c5854458 lib/atoi/, */: Move all a2i() macros to the same file
3:  d54ca4f1 = 3:  5dd7f58a lib/atoi/, */: Move all str2i() macros together with a2i()

v5

Don't use const_cast(). It's hard to make it work properly, so I've moved that to a separate PR.

$ git range-diff shadow/master gh/funclit funclit 
1:  9f7f1574 ! 1:  5d622aad lib/atoi/: a2i(): Re-implement with a statement expression
    @@ lib/atoi/a2i/a2i.h
     +
     +#include "atoi/strtoi/strtoi.h"
     +#include "atoi/strtoi/strtou_noneg.h"
    -+#include "cast.h"
      
      
      /*
    @@ lib/atoi/a2i/a2i.h
     +          unsigned int:       strtou_noneg,                     \
     +          unsigned long:      strtou_noneg,                     \
     +          unsigned long long: strtou_noneg                      \
    -+  )(s, const_cast(char **, endp_), base, min_, max_, &status);  \
    ++  )(s, (char **) endp_, base, min_, max_, &status);             \
     +                                                                      \
     +  if (status != 0)                                              \
     +          errno = status;                                       \
2:  c5854458 = 2:  74e10fba lib/atoi/, */: Move all a2i() macros to the same file
3:  5dd7f58a ! 3:  ff667396 lib/atoi/, */: Move all str2i() macros together with a2i()
    @@ lib/atoi/a2i.h
      
      #include "atoi/strtoi/strtoi.h"
      #include "atoi/strtoi/strtou_noneg.h"
    - #include "cast.h"
     +#include "typetraits.h"

v5b

Rebase

$ git rd 
1:  5d622aad = 1:  248e76bc lib/atoi/: a2i(): Re-implement with a statement expression
2:  74e10fba = 2:  386a90ca lib/atoi/, */: Move all a2i() macros to the same file
3:  ff667396 = 3:  12d4f7de lib/atoi/, */: Move all str2i() macros together with a2i()

v6

Move QChar_of() to a new qchar.h header.

$ git range-diff shadow/master gh/funclit funclit 
-:  -------- > 1:  95744d94 lib/qchar.h: QChar_of(): Add macro
1:  248e76bc ! 2:  9413cf2f lib/atoi/: a2i(): Re-implement with a statement expression
    @@ lib/atoi/a2i/a2i.h
     +
     +#include "atoi/strtoi/strtoi.h"
     +#include "atoi/strtoi/strtou_noneg.h"
    ++#include "qchar.h"
      
      
      /*
    @@ lib/atoi/a2i/a2i.h
     -          void (*)(unsigned long long, char *):        a2ull_nc,        \
     -          void (*)(unsigned long long, void *):        a2ull_nc         \
     -  )(n, s, __VA_ARGS__)                                                  \
    -+// QChar_of - possibly-qualified char of-a-string
    -+#define QChar_of(s)  typeof                                           \
    -+(                                                                     \
    -+  _Generic(s,                                                   \
    -+          const char *:  (const char){1},                       \
    -+          const void *:  (const char){1},                       \
    -+          char *:        (char){1},                             \
    -+          void *:        (char){1}                              \
    -+  )                                                             \
    - )
    - 
    - 
    +-)
     +#define a2i_(T, QChar, n, s, endp, base, min, max)                    \
     +({                                                                    \
     +  T      *n_ = n;                                               \
    @@ lib/atoi/a2i/a2i.h
     +
     +// a2i - alpha to integer
     +#define a2i(T, n, s, ...)  a2i_(T, QChar_of(s), n, s, __VA_ARGS__)
    -+
    -+
    + 
    + 
      #endif  // include guard
     
      ## lib/atoi/a2i/a2s_c.c (deleted) ##
2:  386a90ca = 3:  e19c278c lib/atoi/, */: Move all a2i() macros to the same file
3:  12d4f7de ! 4:  a036cfb7 lib/atoi/, */: Move all str2i() macros together with a2i()
    @@ lib/atoi/a2i.h
      
      #include "atoi/strtoi/strtoi.h"
      #include "atoi/strtoi/strtou_noneg.h"
    + #include "qchar.h"
     +#include "typetraits.h"

v6b

Move QChar_of() to typetraits.h.

$ git range-diff --creation-factor=99 shadow/master gh/funclit funclit 
1:  95744d94 ! 1:  dcb46bfa lib/qchar.h: QChar_of(): Add macro
    @@ Metadata
     Author: Alejandro Colomar <[email protected]>
     
      ## Commit message ##
    -    lib/qchar.h: QChar_of(): Add macro
    +    lib/typetraits.h: QChar_of(): Add macro
     
         This macro is useful to implement QChar versions of functions.
         See ISO C23 for a description of what QChar is.
     
         Signed-off-by: Alejandro Colomar <[email protected]>
     
    - ## lib/Makefile.am ##
    -@@ lib/Makefile.am: libshadow_la_SOURCES = \
    -   pwd2spwd.c \
    -   pwdcheck.c \
    -   pwmem.c \
    -+  qchar.h \
    -   remove_tree.c \
    -   root_flag.c \
    -   run_part.h \
    -
    - ## lib/qchar.h (new) ##
    + ## lib/typetraits.h ##
     @@
    -+// SPDX-FileCopyrightText: 2025, Alejandro Colomar <[email protected]>
    -+// SPDX-License-Identifier: BSD-3-Clause
    -+
    -+
    -+#ifndef SHADOW_INCLUDE_LIB_QCHAR_H_
    -+#define SHADOW_INCLUDE_LIB_QCHAR_H_
    -+
    -+
    -+#include "config.h"
    -+
    -+
    -+// QChar_of - possibly-qualified char of-a-string
    + )
    + 
    + 
     +#define QChar_of(s)  typeof                                           \
     +(                                                                     \
     +  _Generic(s,                                                   \
    @@ lib/qchar.h (new)
     +)
     +
     +
    -+#endif  // include guard
    + #endif  // include guard
2:  9413cf2f ! 2:  84ff1377 lib/atoi/: a2i(): Re-implement with a statement expression
    @@ lib/atoi/a2i/a2i.h
     +
     +#include "atoi/strtoi/strtoi.h"
     +#include "atoi/strtoi/strtou_noneg.h"
    -+#include "qchar.h"
    ++#include "typetraits.h"
      
      
      /*
3:  e19c278c = 3:  10ee4f43 lib/atoi/, */: Move all a2i() macros to the same file
4:  a036cfb7 ! 4:  8f89996a lib/atoi/, */: Move all str2i() macros together with a2i()
    @@ lib/atoi/a2i.h
      
      #include "atoi/strtoi/strtoi.h"
      #include "atoi/strtoi/strtou_noneg.h"
    - #include "qchar.h"
    -+#include "typetraits.h"
    - 
    - 
    - /*
     @@
      #define a2ul(...)   a2i(unsigned long, __VA_ARGS__)
      #define a2ull(...)  a2i(unsigned long long, __VA_ARGS__)

v6c

Rebase

$ git rd 
1:  dcb46bfa = 1:  375e349e lib/typetraits.h: QChar_of(): Add macro
2:  84ff1377 = 2:  1ecc4036 lib/atoi/: a2i(): Re-implement with a statement expression
3:  10ee4f43 ! 3:  7374c784 lib/atoi/, */: Move all a2i() macros to the same file
    @@ Commit message
     
      ## lib/Makefile.am ##
     @@ lib/Makefile.am: libshadow_la_SOURCES = \
    -   alloc/x/xmalloc.h \
    -   alloc/x/xrealloc.c \
    -   alloc/x/xrealloc.h \
    +   alloc/realloc.h \
    +   alloc/reallocf.c \
    +   alloc/reallocf.h \
     -  atoi/a2i/a2i.c \
     -  atoi/a2i/a2i.h \
     -  atoi/a2i/a2s.c \
    @@ lib/idmapping.c
     @@
      
      #include "alloc/calloc.h"
    - #include "alloc/x/xmalloc.h"
    + #include "alloc/malloc.h"
     -#include "atoi/a2i/a2u.h"
     +#include "atoi/a2i.h"
      #include "idmapping.h"
    @@ src/useradd.c
     @@
      #include <unistd.h>
      
    - #include "alloc/x/xmalloc.h"
    + #include "alloc/malloc.h"
     -#include "atoi/a2i/a2s.h"
     +#include "atoi/a2i.h"
      #include "atoi/getnum.h"
    @@ src/useradd.c
     
      ## src/usermod.c ##
     @@
    + #include <time.h>
      
      #include "alloc/malloc.h"
    - #include "alloc/x/xmalloc.h"
     -#include "atoi/a2i/a2i.h"
     -#include "atoi/a2i/a2s.h"
     +#include "atoi/a2i.h"
4:  8f89996a = 4:  f9bb6124 lib/atoi/, */: Move all str2i() macros together with a2i()

alejandro-colomar · 2025-10-18T07:18:50Z

lib/atoi/a2i.h

+#define QChar(s)  typeof                                              \
+(                                                                     \
+	_Generic(s,                                                   \
+		const char *:  *(const char *) "",                    \
+		const void *:  *(const char *) "",                    \
+		char *:        *(char *) "",                          \
+		void *:        *(char *) ""                           \
+	)                                                             \
+)
+
+
+// helper for a2i()
+#define a2i_T(T, QChar, n, s, endp, base, min, max)                   \
+({                                                                    \
+	T      *n_ = n;                                               \
+	QChar  *s_ = s;                                               \
+	QChar  **endp_ = endp;                                        \
+	int    base_ = base;                                          \
+	T      min_ = min;                                            \
+	T      max_ = max;                                            \
+                                                                      \
+	int  status;                                                  \
+                                                                      \
+	*n_ = _Generic(T,                                             \
+		short:              strtoi_,                          \
+		int:                strtoi_,                          \
+		long:               strtoi_,                          \
+		long long:          strtoi_,                          \
+		unsigned short:     strtou_noneg,                     \
+		unsigned int:       strtou_noneg,                     \
+		unsigned long:      strtou_noneg,                     \
+		unsigned long long: strtou_noneg                      \
+	)(s_, const_cast(char **, endp_), base_, min_, max_, &status);\
+                                                                      \
+	if (status != 0)                                              \
+		errno = status;                                       \
+	status == 0 ? 0 : -1;                                         \
+})
+
+
+// a2i - alpha to integer
+#define a2i(T, n, s, ...)  a2i_T(T, QChar(s), n, s, __VA_ARGS__)
+
+#define a2sh(...)   a2i(short, __VA_ARGS__)
+#define a2si(...)   a2i(int, __VA_ARGS__)
+#define a2sl(...)   a2i(long, __VA_ARGS__)
+#define a2sll(...)  a2i(long long, __VA_ARGS__)
+
+#define a2uh(...)   a2i(unsigned short, __VA_ARGS__)
+#define a2ui(...)   a2i(unsigned int, __VA_ARGS__)
+#define a2ul(...)   a2i(unsigned long, __VA_ARGS__)
+#define a2ull(...)  a2i(unsigned long long, __VA_ARGS__)
+
+#define str2i(T, ...)  a2i(T, __VA_ARGS__, NULL, 0, type_min(T), type_max(T))
+
+#define str2sh(...)    str2i(short, __VA_ARGS__)
+#define str2si(...)    str2i(int, __VA_ARGS__)
+#define str2sl(...)    str2i(long, __VA_ARGS__)
+#define str2sll(...)   str2i(long long, __VA_ARGS__)
+
+#define str2uh(...)    str2i(unsigned short, __VA_ARGS__)
+#define str2ui(...)    str2i(unsigned int, __VA_ARGS__)
+#define str2ul(...)    str2i(unsigned long, __VA_ARGS__)
+#define str2ull(...)   str2i(unsigned long long, __VA_ARGS__)


I've finally removed the need to read many layers of files, macros, and functions to understand what these APIs do!

Finally, this API set is much more readable now. :)

Cc: @ikerexxe , @thesamesam

(There's still strtoi_() and strtou_noneg(), but those are really necessary.)

This macro is useful to implement QChar versions of functions. See ISO C23 for a description of what QChar is. Signed-off-by: Alejandro Colomar <[email protected]>

Signed-off-by: Alejandro Colomar <[email protected]>

alejandro-colomar changed the title ~~a2i(): Simplify, a lot~~ a2i(): Simplify, a lot; really! Oct 18, 2025

alejandro-colomar force-pushed the funclit branch 3 times, most recently from cb1c2f7 to b9472c3 Compare October 18, 2025 07:17

alejandro-colomar commented Oct 18, 2025

View reviewed changes

alejandro-colomar force-pushed the funclit branch 5 times, most recently from 0f7e3f7 to d83e5e2 Compare October 18, 2025 07:36

alejandro-colomar changed the title ~~a2i(): Simplify, a lot; really!~~ a2i(): Minimal minimalism Oct 18, 2025

alejandro-colomar changed the title ~~a2i(): Minimal minimalism~~ a2i(): Maximal minimalism Oct 18, 2025

alejandro-colomar force-pushed the funclit branch from d83e5e2 to 47c20df Compare October 18, 2025 08:01

alejandro-colomar marked this pull request as ready for review October 18, 2025 08:24

alejandro-colomar requested review from hallyn and ikerexxe October 18, 2025 08:24

alejandro-colomar force-pushed the funclit branch 6 times, most recently from 5dd7f58 to ff66739 Compare October 18, 2025 18:38

alejandro-colomar mentioned this pull request Oct 18, 2025

Generalize const_cast(), and use it more. #1374

Draft

alejandro-colomar force-pushed the funclit branch 3 times, most recently from a036cfb to 8f89996 Compare October 19, 2025 08:22

alejandro-colomar added 4 commits October 27, 2025 14:55

lib/typetraits.h: QChar_of(): Add macro

375e349

This macro is useful to implement QChar versions of functions. See ISO C23 for a description of what QChar is. Signed-off-by: Alejandro Colomar <[email protected]>

lib/atoi/: a2i(): Re-implement with a statement expression

1ecc403

Signed-off-by: Alejandro Colomar <[email protected]>

lib/atoi/, */: Move all a2i() macros to the same file

7374c78

Signed-off-by: Alejandro Colomar <[email protected]>

lib/atoi/, */: Move all str2i() macros together with a2i()

f9bb612

Signed-off-by: Alejandro Colomar <[email protected]>

alejandro-colomar force-pushed the funclit branch from 8f89996 to f9bb612 Compare October 27, 2025 13:59

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