[libcxx-commits] [libcxx] [libc++] Implement our own is{, x}digit functions for the C locale (PR #165467)

[Nikolas Klauser via libcxx-commits]

https://github.com/philnik777 created https://github.com/llvm/llvm-project/pull/165467

The C locale is defined by the C standard, so we know exactly which digits classify as (x)digits. Instead of going through the locale base API we can simply implement functions which determine whether a charachter is one ourselves, and probably improve code gen significantly as well that way.


>From 4f59971aea2dc1bb390b79a30393daec0b7e97a2 Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Tue, 28 Oct 2025 20:37:15 +0100
Subject: [PATCH] [libc++] Implement our own is{,x}digit functions for the C
 locale

---
 libcxx/include/__locale_dir/locale_base_api.h       |  5 -----
 libcxx/include/__locale_dir/num.h                   | 13 +++++++++++--
 libcxx/include/__locale_dir/support/bsd_like.h      |  4 ----
 libcxx/include/__locale_dir/support/linux.h         |  4 ----
 .../__locale_dir/support/no_locale/characters.h     |  4 ----
 libcxx/include/__locale_dir/support/windows.h       |  4 ----
 6 files changed, 11 insertions(+), 23 deletions(-)

diff --git a/libcxx/include/__locale_dir/locale_base_api.h b/libcxx/include/__locale_dir/locale_base_api.h
index 9f3ce02a3af20..152eccee1cdda 100644
--- a/libcxx/include/__locale_dir/locale_base_api.h
+++ b/libcxx/include/__locale_dir/locale_base_api.h
@@ -64,8 +64,6 @@
 // Character manipulation functions
 // --------------------------------
 // namespace __locale {
-//  int     __isdigit(int, __locale_t);  // required by the headers
-//  int     __isxdigit(int, __locale_t); // required by the headers
 //  int     __toupper(int, __locale_t);
 //  int     __tolower(int, __locale_t);
 //  int     __strcoll(const char*, const char*, __locale_t);
@@ -204,9 +202,6 @@ __strtoull(const char* __nptr, char** __endptr, int __base, __locale_t __loc) {
 //
 // Character manipulation functions
 //
-inline _LIBCPP_HIDE_FROM_ABI int __isdigit(int __ch, __locale_t __loc) { return isdigit_l(__ch, __loc); }
-inline _LIBCPP_HIDE_FROM_ABI int __isxdigit(int __ch, __locale_t __loc) { return isxdigit_l(__ch, __loc); }
-
 #    if defined(_LIBCPP_BUILDING_LIBRARY)
 inline _LIBCPP_HIDE_FROM_ABI int __strcoll(const char* __s1, const char* __s2, __locale_t __loc) {
   return strcoll_l(__s1, __s2, __loc);
diff --git a/libcxx/include/__locale_dir/num.h b/libcxx/include/__locale_dir/num.h
index 7ca8ffe348959..224d7b9d2c668 100644
--- a/libcxx/include/__locale_dir/num.h
+++ b/libcxx/include/__locale_dir/num.h
@@ -748,6 +748,15 @@ void __num_put<_CharT>::__widen_and_group_int(
     __op = __ob + (__np - __nb);
 }
 
+_LIBCPP_HIDE_FROM_ABI inline bool __isdigit(char __c) {
+  return __c >= '0' && __c <= '9';
+}
+
+_LIBCPP_HIDE_FROM_ABI inline bool __isxdigit(char __c) {
+  auto __lower = __c | 0x20;
+  return std::__isdigit(__c) || (__lower >= 'a' && __lower <= 'f');
+}
+
 template <class _CharT>
 void __num_put<_CharT>::__widen_and_group_float(
     char* __nb, char* __np, char* __ne, _CharT* __ob, _CharT*& __op, _CharT*& __oe, const locale& __loc) {
@@ -763,11 +772,11 @@ void __num_put<_CharT>::__widen_and_group_float(
     *__oe++ = __ct.widen(*__nf++);
     *__oe++ = __ct.widen(*__nf++);
     for (__ns = __nf; __ns < __ne; ++__ns)
-      if (!__locale::__isxdigit(*__ns, _LIBCPP_GET_C_LOCALE))
+      if (!std::__isxdigit(*__ns))
         break;
   } else {
     for (__ns = __nf; __ns < __ne; ++__ns)
-      if (!__locale::__isdigit(*__ns, _LIBCPP_GET_C_LOCALE))
+      if (!std::__isdigit(*__ns))
         break;
   }
   if (__grouping.empty()) {
diff --git a/libcxx/include/__locale_dir/support/bsd_like.h b/libcxx/include/__locale_dir/support/bsd_like.h
index ac402924709e5..568cc17993cf8 100644
--- a/libcxx/include/__locale_dir/support/bsd_like.h
+++ b/libcxx/include/__locale_dir/support/bsd_like.h
@@ -89,10 +89,6 @@ __strtoull(const char* __nptr, char** __endptr, int __base, __locale_t __loc) {
 //
 // Character manipulation functions
 //
-inline _LIBCPP_HIDE_FROM_ABI int __isdigit(int __c, __locale_t __loc) { return ::isdigit_l(__c, __loc); }
-
-inline _LIBCPP_HIDE_FROM_ABI int __isxdigit(int __c, __locale_t __loc) { return ::isxdigit_l(__c, __loc); }
-
 #if defined(_LIBCPP_BUILDING_LIBRARY)
 inline _LIBCPP_HIDE_FROM_ABI int __toupper(int __c, __locale_t __loc) { return ::toupper_l(__c, __loc); }
 
diff --git a/libcxx/include/__locale_dir/support/linux.h b/libcxx/include/__locale_dir/support/linux.h
index 23bcf44c31dbf..94a2ecb9a940d 100644
--- a/libcxx/include/__locale_dir/support/linux.h
+++ b/libcxx/include/__locale_dir/support/linux.h
@@ -116,10 +116,6 @@ __strtoull(const char* __nptr, char** __endptr, int __base, __locale_t __loc) {
 //
 // Character manipulation functions
 //
-inline _LIBCPP_HIDE_FROM_ABI int __isdigit(int __c, __locale_t __loc) { return isdigit_l(__c, __loc); }
-
-inline _LIBCPP_HIDE_FROM_ABI int __isxdigit(int __c, __locale_t __loc) { return isxdigit_l(__c, __loc); }
-
 #if defined(_LIBCPP_BUILDING_LIBRARY)
 inline _LIBCPP_HIDE_FROM_ABI int __toupper(int __c, __locale_t __loc) { return toupper_l(__c, __loc); }
 
diff --git a/libcxx/include/__locale_dir/support/no_locale/characters.h b/libcxx/include/__locale_dir/support/no_locale/characters.h
index 1281b8bd13094..73eba3ec542c7 100644
--- a/libcxx/include/__locale_dir/support/no_locale/characters.h
+++ b/libcxx/include/__locale_dir/support/no_locale/characters.h
@@ -29,10 +29,6 @@ namespace __locale {
 //
 // Character manipulation functions
 //
-inline _LIBCPP_HIDE_FROM_ABI int __isdigit(int __c, __locale_t) { return std::isdigit(__c); }
-
-inline _LIBCPP_HIDE_FROM_ABI int __isxdigit(int __c, __locale_t) { return std::isxdigit(__c); }
-
 #if defined(_LIBCPP_BUILDING_LIBRARY)
 inline _LIBCPP_HIDE_FROM_ABI int __toupper(int __c, __locale_t) { return std::toupper(__c); }
 
diff --git a/libcxx/include/__locale_dir/support/windows.h b/libcxx/include/__locale_dir/support/windows.h
index 0df8709f118d0..edd8a66c23e80 100644
--- a/libcxx/include/__locale_dir/support/windows.h
+++ b/libcxx/include/__locale_dir/support/windows.h
@@ -197,10 +197,6 @@ __strtoull(const char* __nptr, char** __endptr, int __base, __locale_t __loc) {
 //
 // Character manipulation functions
 //
-inline _LIBCPP_HIDE_FROM_ABI int __isdigit(int __c, __locale_t __loc) { return _isdigit_l(__c, __loc); }
-
-inline _LIBCPP_HIDE_FROM_ABI int __isxdigit(int __c, __locale_t __loc) { return _isxdigit_l(__c, __loc); }
-
 #if defined(_LIBCPP_BUILDING_LIBRARY)
 inline _LIBCPP_HIDE_FROM_ABI int __toupper(int __c, __locale_t __loc) { return ::_toupper_l(__c, __loc); }