diff --git a/libc/tzcode/private.h b/libc/tzcode/private.h
index 4c03324..838ab2b 100644
--- a/libc/tzcode/private.h
+++ b/libc/tzcode/private.h
@@ -17,6 +17,36 @@
 ** Thank you!
 */
 
+/* PORT_TO_C89 means the code should work even if the underlying
+   compiler and library support only C89.  SUPPORT_C89 means the
+   tzcode library should support C89 callers in addition to the usual
+   support for C99-and-later callers.  These macros are obsolescent,
+   and the plan is to remove them along with any code needed only when
+   they are nonzero.  */
+#ifndef PORT_TO_C89
+# define PORT_TO_C89 0
+#endif
+#ifndef SUPPORT_C89
+# define SUPPORT_C89 0
+#endif
+
+#ifndef __STDC_VERSION__
+# define __STDC_VERSION__ 0
+#endif
+
+/* Define true, false and bool if they don't work out of the box.  */
+#if PORT_TO_C89 && __STDC_VERSION__ < 199901
+# define true 1
+# define false 0
+# define bool int
+#elif __STDC_VERSION__ < 202311
+# include <stdbool.h>
+#endif
+
+#if __STDC_VERSION__ < 202311
+# define static_assert(cond) extern int static_assert_check[(cond) ? 1 : -1]
+#endif
+
 /*
 ** zdump has been made independent of the rest of the time
 ** conversion package to increase confidence in the verification it provides.
@@ -36,79 +66,86 @@
 */
 
 #ifndef HAVE_DECL_ASCTIME_R
-#define HAVE_DECL_ASCTIME_R 1
+# define HAVE_DECL_ASCTIME_R 1
 #endif
 
-#if !defined HAVE_GENERIC && defined __has_extension
+#if !defined HAVE__GENERIC && defined __has_extension
 # if __has_extension(c_generic_selections)
-#  define HAVE_GENERIC 1
+#  define HAVE__GENERIC 1
 # else
-#  define HAVE_GENERIC 0
+#  define HAVE__GENERIC 0
 # endif
 #endif
 /* _Generic is buggy in pre-4.9 GCC.  */
-#if !defined HAVE_GENERIC && defined __GNUC__
-# define HAVE_GENERIC (4 < __GNUC__ + (9 <= __GNUC_MINOR__))
+#if !defined HAVE__GENERIC && defined __GNUC__ && !defined __STRICT_ANSI__
+# define HAVE__GENERIC (4 < __GNUC__ + (9 <= __GNUC_MINOR__))
 #endif
-#ifndef HAVE_GENERIC
-# define HAVE_GENERIC (201112 <= __STDC_VERSION__)
+#ifndef HAVE__GENERIC
+# define HAVE__GENERIC (201112 <= __STDC_VERSION__)
 #endif
 
+#if !defined HAVE_GETTEXT && defined __has_include
+# if __has_include(<libintl.h>)
+#  define HAVE_GETTEXT true
+# endif
+#endif
 #ifndef HAVE_GETTEXT
-#define HAVE_GETTEXT		0
-#endif /* !defined HAVE_GETTEXT */
+# define HAVE_GETTEXT false
+#endif
 
 #ifndef HAVE_INCOMPATIBLE_CTIME_R
-#define HAVE_INCOMPATIBLE_CTIME_R	0
+# define HAVE_INCOMPATIBLE_CTIME_R 0
 #endif
 
 #ifndef HAVE_LINK
-#define HAVE_LINK		1
+# define HAVE_LINK 1
 #endif /* !defined HAVE_LINK */
 
 #ifndef HAVE_MALLOC_ERRNO
-#define HAVE_MALLOC_ERRNO 1
+# define HAVE_MALLOC_ERRNO 1
 #endif
 
 #ifndef HAVE_POSIX_DECLS
-#define HAVE_POSIX_DECLS 1
+# define HAVE_POSIX_DECLS 1
 #endif
 
-#ifndef HAVE_STDBOOL_H
-#define HAVE_STDBOOL_H (199901 <= __STDC_VERSION__)
+#ifndef HAVE_SETENV
+# define HAVE_SETENV 1
 #endif
 
 #ifndef HAVE_STRDUP
-#define HAVE_STRDUP 1
-#endif
-
-#ifndef HAVE_STRTOLL
-#define HAVE_STRTOLL 1
+# define HAVE_STRDUP 1
 #endif
 
 #ifndef HAVE_SYMLINK
-#define HAVE_SYMLINK		1
+# define HAVE_SYMLINK 1
 #endif /* !defined HAVE_SYMLINK */
 
+#if !defined HAVE_SYS_STAT_H && defined __has_include
+# if !__has_include(<sys/stat.h>)
+#  define HAVE_SYS_STAT_H false
+# endif
+#endif
 #ifndef HAVE_SYS_STAT_H
-#define HAVE_SYS_STAT_H		1
-#endif /* !defined HAVE_SYS_STAT_H */
+# define HAVE_SYS_STAT_H true
+#endif
 
+#if !defined HAVE_UNISTD_H && defined __has_include
+# if !__has_include(<unistd.h>)
+#  define HAVE_UNISTD_H false
+# endif
+#endif
 #ifndef HAVE_UNISTD_H
-#define HAVE_UNISTD_H		1
-#endif /* !defined HAVE_UNISTD_H */
-
-#ifndef HAVE_UTMPX_H
-#define HAVE_UTMPX_H		1
-#endif /* !defined HAVE_UTMPX_H */
+# define HAVE_UNISTD_H true
+#endif
 
 #ifndef NETBSD_INSPIRED
 # define NETBSD_INSPIRED 1
 #endif
 
 #if HAVE_INCOMPATIBLE_CTIME_R
-#define asctime_r _incompatible_asctime_r
-#define ctime_r _incompatible_ctime_r
+# define asctime_r _incompatible_asctime_r
+# define ctime_r _incompatible_ctime_r
 #endif /* HAVE_INCOMPATIBLE_CTIME_R */
 
 /* Enable tm_gmtoff, tm_zone, and environ on GNUish systems.  */
@@ -118,15 +155,17 @@
 /* Enable strtoimax on pre-C99 Solaris 11.  */
 #define __EXTENSIONS__ 1
 
-/* To avoid having 'stat' fail unnecessarily with errno == EOVERFLOW,
-   enable large files on GNUish systems ...  */
+/* On GNUish systems where time_t might be 32 or 64 bits, use 64.
+   On these platforms _FILE_OFFSET_BITS must also be 64; otherwise
+   setting _TIME_BITS to 64 does not work.  The code does not
+   otherwise rely on _FILE_OFFSET_BITS being 64, since it does not
+   use off_t or functions like 'stat' that depend on off_t.  */
 #ifndef _FILE_OFFSET_BITS
 # define _FILE_OFFSET_BITS 64
 #endif
-/* ... and on AIX ...  */
-#define _LARGE_FILES 1
-/* ... and enable large inode numbers on Mac OS X 10.5 and later.  */
-#define _DARWIN_USE_64_BIT_INODE 1
+#if !defined _TIME_BITS && _FILE_OFFSET_BITS == 64
+# define _TIME_BITS 64
+#endif
 
 /*
 ** Nested includes
@@ -157,8 +196,11 @@
 #undef tzalloc
 #undef tzfree
 
-#include <sys/types.h>	/* for time_t */
+#include <stddef.h>
 #include <string.h>
+#if !PORT_TO_C89
+# include <inttypes.h>
+#endif
 #include <limits.h>	/* for CHAR_BIT et al. */
 #include <stdlib.h>
 
@@ -168,6 +210,9 @@
 # define EINVAL ERANGE
 #endif
 
+#ifndef ELOOP
+# define ELOOP EINVAL
+#endif
 #ifndef ENAMETOOLONG
 # define ENAMETOOLONG EINVAL
 #endif
@@ -182,11 +227,11 @@
 #endif
 
 #if HAVE_GETTEXT
-#include <libintl.h>
+# include <libintl.h>
 #endif /* HAVE_GETTEXT */
 
 #if HAVE_UNISTD_H
-#include <unistd.h>	/* for R_OK, and other POSIX goodness */
+# include <unistd.h> /* for R_OK, and other POSIX goodness */
 #endif /* HAVE_UNISTD_H */
 
 #ifndef HAVE_STRFTIME_L
@@ -222,24 +267,29 @@
 #endif
 
 #ifndef R_OK
-#define R_OK	4
+# define R_OK 4
 #endif /* !defined R_OK */
 
+#if PORT_TO_C89
+
 /*
 ** Define HAVE_STDINT_H's default value here, rather than at the
 ** start, since __GLIBC__ and INTMAX_MAX's values depend on
-** previously-included files.  glibc 2.1 and Solaris 10 and later have
+** previously included files.  glibc 2.1 and Solaris 10 and later have
 ** stdint.h, even with pre-C99 compilers.
 */
+#if !defined HAVE_STDINT_H && defined __has_include
+# define HAVE_STDINT_H true /* C23 __has_include implies C99 stdint.h.  */
+#endif
 #ifndef HAVE_STDINT_H
-#define HAVE_STDINT_H \
+# define HAVE_STDINT_H \
    (199901 <= __STDC_VERSION__ \
-    || 2 < __GLIBC__ + (1 <= __GLIBC_MINOR__)	\
+    || 2 < __GLIBC__ + (1 <= __GLIBC_MINOR__) \
     || __CYGWIN__ || INTMAX_MAX)
 #endif /* !defined HAVE_STDINT_H */
 
 #if HAVE_STDINT_H
-#include <stdint.h>
+# include <stdint.h>
 #endif /* !HAVE_STDINT_H */
 
 #ifndef HAVE_INTTYPES_H
@@ -250,36 +300,36 @@
 #endif
 
 /* Pre-C99 GCC compilers define __LONG_LONG_MAX__ instead of LLONG_MAX.  */
-#ifdef __LONG_LONG_MAX__
+#if defined __LONG_LONG_MAX__ && !defined __STRICT_ANSI__
 # ifndef LLONG_MAX
 #  define LLONG_MAX __LONG_LONG_MAX__
 # endif
 # ifndef LLONG_MIN
 #  define LLONG_MIN (-1 - LLONG_MAX)
 # endif
+# ifndef ULLONG_MAX
+#  define ULLONG_MAX (LLONG_MAX * 2ull + 1)
+# endif
 #endif
 
 #ifndef INT_FAST64_MAX
-# ifdef LLONG_MAX
-typedef long long	int_fast64_t;
-#  define INT_FAST64_MIN LLONG_MIN
-#  define INT_FAST64_MAX LLONG_MAX
-# else
-#  if LONG_MAX >> 31 < 0xffffffff
-Please use a compiler that supports a 64-bit integer type (or wider);
-you may need to compile with "-DHAVE_STDINT_H".
-#  endif
-typedef long		int_fast64_t;
+# if 1 <= LONG_MAX >> 31 >> 31
+typedef long int_fast64_t;
 #  define INT_FAST64_MIN LONG_MIN
 #  define INT_FAST64_MAX LONG_MAX
+# else
+/* If this fails, compile with -DHAVE_STDINT_H or with a better compiler.  */
+typedef long long int_fast64_t;
+#  define INT_FAST64_MIN LLONG_MIN
+#  define INT_FAST64_MAX LLONG_MAX
 # endif
 #endif
 
 #ifndef PRIdFAST64
-# if INT_FAST64_MAX == LLONG_MAX
-#  define PRIdFAST64 "lld"
-# else
+# if INT_FAST64_MAX == LONG_MAX
 #  define PRIdFAST64 "ld"
+# else
+#  define PRIdFAST64 "lld"
 # endif
 #endif
 
@@ -302,6 +352,9 @@
 #ifndef INTMAX_MAX
 # ifdef LLONG_MAX
 typedef long long intmax_t;
+#  ifndef HAVE_STRTOLL
+#   define HAVE_STRTOLL true
+#  endif
 #  if HAVE_STRTOLL
 #   define strtoimax strtoll
 #  endif
@@ -325,70 +378,183 @@
 # endif
 #endif
 
+#ifndef PTRDIFF_MAX
+# define PTRDIFF_MAX MAXVAL(ptrdiff_t, TYPE_BIT(ptrdiff_t))
+#endif
+
 #ifndef UINT_FAST32_MAX
 typedef unsigned long uint_fast32_t;
 #endif
 
 #ifndef UINT_FAST64_MAX
-# if defined ULLONG_MAX || defined __LONG_LONG_MAX__
-typedef unsigned long long uint_fast64_t;
+# if 3 <= ULONG_MAX >> 31 >> 31
+typedef unsigned long uint_fast64_t;
+#  define UINT_FAST64_MAX ULONG_MAX
 # else
-#  if ULONG_MAX >> 31 >> 1 < 0xffffffff
-Please use a compiler that supports a 64-bit integer type (or wider);
-you may need to compile with "-DHAVE_STDINT_H".
-#  endif
-typedef unsigned long	uint_fast64_t;
+/* If this fails, compile with -DHAVE_STDINT_H or with a better compiler.  */
+typedef unsigned long long uint_fast64_t;
+#  define UINT_FAST64_MAX ULLONG_MAX
 # endif
 #endif
 
 #ifndef UINTMAX_MAX
-# if defined ULLONG_MAX || defined __LONG_LONG_MAX__
+# ifdef ULLONG_MAX
 typedef unsigned long long uintmax_t;
+#  define UINTMAX_MAX ULLONG_MAX
 # else
 typedef unsigned long uintmax_t;
+#  define UINTMAX_MAX ULONG_MAX
 # endif
 #endif
 
 #ifndef PRIuMAX
-# if defined ULLONG_MAX || defined __LONG_LONG_MAX__
+# ifdef ULLONG_MAX
 #  define PRIuMAX "llu"
 # else
 #  define PRIuMAX "lu"
 # endif
 #endif
 
-#ifndef INT32_MAX
-#define INT32_MAX 0x7fffffff
-#endif /* !defined INT32_MAX */
-#ifndef INT32_MIN
-#define INT32_MIN (-1 - INT32_MAX)
-#endif /* !defined INT32_MIN */
-
 #ifndef SIZE_MAX
-#define SIZE_MAX ((size_t) -1)
+# define SIZE_MAX ((size_t) -1)
+#endif
+
+#endif /* PORT_TO_C89 */
+
+/* The maximum size of any created object, as a signed integer.
+   Although the C standard does not outright prohibit larger objects,
+   behavior is undefined if the result of pointer subtraction does not
+   fit into ptrdiff_t, and the code assumes in several places that
+   pointer subtraction works.  As a practical matter it's OK to not
+   support objects larger than this.  */
+#define INDEX_MAX ((ptrdiff_t) min(PTRDIFF_MAX, SIZE_MAX))
+
+/* Support ckd_add, ckd_sub, ckd_mul on C23 or recent-enough GCC-like
+   hosts, unless compiled with -DHAVE_STDCKDINT_H=0 or with pre-C23 EDG.  */
+#if !defined HAVE_STDCKDINT_H && defined __has_include
+# if __has_include(<stdckdint.h>)
+#  define HAVE_STDCKDINT_H true
+# endif
+#endif
+#ifdef HAVE_STDCKDINT_H
+# if HAVE_STDCKDINT_H
+#  include <stdckdint.h>
+# endif
+#elif defined __EDG__
+/* Do nothing, to work around EDG bug <https://bugs.gnu.org/53256>.  */
+#elif defined __has_builtin
+# if __has_builtin(__builtin_add_overflow)
+#  define ckd_add(r, a, b) __builtin_add_overflow(a, b, r)
+# endif
+# if __has_builtin(__builtin_sub_overflow)
+#  define ckd_sub(r, a, b) __builtin_sub_overflow(a, b, r)
+# endif
+# if __has_builtin(__builtin_mul_overflow)
+#  define ckd_mul(r, a, b) __builtin_mul_overflow(a, b, r)
+# endif
+#elif 7 <= __GNUC__
+# 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)
 #endif
 
 #if 3 <= __GNUC__
-# define ATTRIBUTE_CONST __attribute__((const))
-# define ATTRIBUTE_MALLOC __attribute__((__malloc__))
-# define ATTRIBUTE_PURE __attribute__((__pure__))
-# define ATTRIBUTE_FORMAT(spec) __attribute__((__format__ spec))
+# define ATTRIBUTE_MALLOC __attribute__((malloc))
+# define ATTRIBUTE_FORMAT(spec) __attribute__((format spec))
 #else
-# define ATTRIBUTE_CONST /* empty */
 # define ATTRIBUTE_MALLOC /* empty */
-# define ATTRIBUTE_PURE /* empty */
 # define ATTRIBUTE_FORMAT(spec) /* empty */
 #endif
 
-#if !defined _Noreturn && __STDC_VERSION__ < 201112
-# if 2 < __GNUC__ + (8 <= __GNUC_MINOR__)
-#  define _Noreturn __attribute__((__noreturn__))
+#if (defined __has_c_attribute \
+     && (202311 <= __STDC_VERSION__ || !defined __STRICT_ANSI__))
+# define HAVE___HAS_C_ATTRIBUTE true
+#else
+# define HAVE___HAS_C_ATTRIBUTE false
+#endif
+
+#if HAVE___HAS_C_ATTRIBUTE
+# if __has_c_attribute(deprecated)
+#  define ATTRIBUTE_DEPRECATED [[deprecated]]
+# endif
+#endif
+#ifndef ATTRIBUTE_DEPRECATED
+# if 3 < __GNUC__ + (2 <= __GNUC_MINOR__)
+#  define ATTRIBUTE_DEPRECATED __attribute__((deprecated))
 # else
-#  define _Noreturn
+#  define ATTRIBUTE_DEPRECATED /* empty */
 # endif
 #endif
 
-#if __STDC_VERSION__ < 199901 && !defined restrict
+#if HAVE___HAS_C_ATTRIBUTE
+# if __has_c_attribute(fallthrough)
+#  define ATTRIBUTE_FALLTHROUGH [[fallthrough]]
+# endif
+#endif
+#ifndef ATTRIBUTE_FALLTHROUGH
+# if 7 <= __GNUC__
+#  define ATTRIBUTE_FALLTHROUGH __attribute__((fallthrough))
+# else
+#  define ATTRIBUTE_FALLTHROUGH ((void) 0)
+# endif
+#endif
+
+#if HAVE___HAS_C_ATTRIBUTE
+# if __has_c_attribute(maybe_unused)
+#  define ATTRIBUTE_MAYBE_UNUSED [[maybe_unused]]
+# endif
+#endif
+#ifndef ATTRIBUTE_MAYBE_UNUSED
+# if 2 < __GNUC__ + (7 <= __GNUC_MINOR__)
+#  define ATTRIBUTE_MAYBE_UNUSED __attribute__((unused))
+# else
+#  define ATTRIBUTE_MAYBE_UNUSED /* empty */
+# endif
+#endif
+
+#if HAVE___HAS_C_ATTRIBUTE
+# if __has_c_attribute(noreturn)
+#  define ATTRIBUTE_NORETURN [[noreturn]]
+# endif
+#endif
+#ifndef ATTRIBUTE_NORETURN
+# if 201112 <= __STDC_VERSION__
+#  define ATTRIBUTE_NORETURN _Noreturn
+# elif 2 < __GNUC__ + (8 <= __GNUC_MINOR__)
+#  define ATTRIBUTE_NORETURN __attribute__((noreturn))
+# else
+#  define ATTRIBUTE_NORETURN /* empty */
+# endif
+#endif
+
+#if HAVE___HAS_C_ATTRIBUTE
+# if __has_c_attribute(reproducible)
+#  define ATTRIBUTE_REPRODUCIBLE [[reproducible]]
+# endif
+#endif
+#ifndef ATTRIBUTE_REPRODUCIBLE
+# if 3 <= __GNUC__
+#  define ATTRIBUTE_REPRODUCIBLE __attribute__((pure))
+# else
+#  define ATTRIBUTE_REPRODUCIBLE /* empty */
+# endif
+#endif
+
+#if HAVE___HAS_C_ATTRIBUTE
+# if __has_c_attribute(unsequenced)
+#  define ATTRIBUTE_UNSEQUENCED [[unsequenced]]
+# endif
+#endif
+#ifndef ATTRIBUTE_UNSEQUENCED
+# if 3 <= __GNUC__
+#  define ATTRIBUTE_UNSEQUENCED __attribute__((const))
+# else
+#  define ATTRIBUTE_UNSEQUENCED /* empty */
+# endif
+#endif
+
+#if (__STDC_VERSION__ < 199901 && !defined restrict \
+     && (PORT_TO_C89 || defined _MSC_VER))
 # define restrict /* empty */
 #endif
 
@@ -505,11 +671,16 @@
 #  define altzone tz_altzone
 # endif
 
-char *asctime(struct tm const *);
+# if __STDC_VERSION__ < 202311
+#  define DEPRECATED_IN_C23 /* empty */
+# else
+#  define DEPRECATED_IN_C23 ATTRIBUTE_DEPRECATED
+# endif
+DEPRECATED_IN_C23 char *asctime(struct tm const *);
 char *asctime_r(struct tm const *restrict, char *restrict);
-char *ctime(time_t const *);
+DEPRECATED_IN_C23 char *ctime(time_t const *);
 char *ctime_r(time_t const *, char *);
-double difftime(time_t, time_t) ATTRIBUTE_CONST;
+ATTRIBUTE_UNSEQUENCED double difftime(time_t, time_t);
 size_t strftime(char *restrict, size_t, char const *restrict,
 		struct tm const *restrict);
 # if HAVE_STRFTIME_L
@@ -522,9 +693,24 @@
 struct tm *localtime_r(time_t const *restrict, struct tm *restrict);
 time_t mktime(struct tm *);
 time_t time(time_t *);
+time_t timegm(struct tm *);
 void tzset(void);
 #endif
 
+#ifndef HAVE_DECL_TIMEGM
+# if (202311 <= __STDC_VERSION__ \
+      || defined __GLIBC__ || defined __tm_zone /* musl */ \
+      || defined __FreeBSD__ || defined __NetBSD__ || defined __OpenBSD__ \
+      || (defined __APPLE__ && defined __MACH__))
+#  define HAVE_DECL_TIMEGM true
+# else
+#  define HAVE_DECL_TIMEGM false
+# endif
+#endif
+#if !HAVE_DECL_TIMEGM && !defined timegm
+time_t timegm(struct tm *);
+#endif
+
 #if !HAVE_DECL_ASCTIME_R && !defined asctime_r
 extern char *asctime_r(struct tm const *restrict, char *restrict);
 #endif
@@ -557,13 +743,13 @@
 ** declarations if time_tz is defined.
 */
 
-#ifdef STD_INSPIRED
+#ifndef STD_INSPIRED
+# define STD_INSPIRED 0
+#endif
+#if STD_INSPIRED
 # if TZ_TIME_T || !defined offtime
 struct tm *offtime(time_t const *, long);
 # endif
-# if TZ_TIME_T || !defined timegm
-time_t timegm(struct tm *);
-# endif
 # if TZ_TIME_T || !defined timelocal
 time_t timelocal(struct tm *);
 # endif
@@ -581,6 +767,7 @@
 /* Infer TM_ZONE on systems where this information is known, but suppress
    guessing if NO_TM_ZONE is defined.  Similarly for TM_GMTOFF.  */
 #if (defined __GLIBC__ \
+     || defined __tm_zone /* musl */ \
      || defined __FreeBSD__ || defined __NetBSD__ || defined __OpenBSD__ \
      || (defined __APPLE__ && defined __MACH__))
 # if !defined TM_GMTOFF && !defined NO_TM_GMTOFF
@@ -606,12 +793,12 @@
 time_t mktime_z(timezone_t restrict, struct tm *restrict);
 timezone_t tzalloc(char const *);
 void tzfree(timezone_t);
-# ifdef STD_INSPIRED
+# if STD_INSPIRED
 #  if TZ_TIME_T || !defined posix2time_z
-time_t posix2time_z(timezone_t, time_t) ATTRIBUTE_PURE;
+ATTRIBUTE_REPRODUCIBLE time_t posix2time_z(timezone_t, time_t);
 #  endif
 #  if TZ_TIME_T || !defined time2posix_z
-time_t time2posix_z(timezone_t, time_t) ATTRIBUTE_PURE;
+ATTRIBUTE_REPRODUCIBLE time_t time2posix_z(timezone_t, time_t);
 #  endif
 # endif
 #endif
@@ -620,18 +807,15 @@
 ** Finally, some convenience items.
 */
 
-#if HAVE_STDBOOL_H
-# include <stdbool.h>
-#else
-# define true 1
-# define false 0
-# define bool int
-#endif
-
-#define TYPE_BIT(type)	(sizeof(type) * CHAR_BIT)
+#define TYPE_BIT(type) (CHAR_BIT * (ptrdiff_t) sizeof(type))
 #define TYPE_SIGNED(type) (((type) -1) < 0)
 #define TWOS_COMPLEMENT(t) ((t) ~ (t) 0 < 0)
 
+/* Minimum and maximum of two values.  Use lower case to avoid
+   naming clashes with standard include files.  */
+#define max(a, b) ((a) > (b) ? (a) : (b))
+#define min(a, b) ((a) < (b) ? (a) : (b))
+
 /* Max and min values of the integer type T, of which only the bottom
    B bits are used, and where the highest-order used bit is considered
    to be a sign bit if T is signed.  */
@@ -651,7 +835,7 @@
    This implementation assumes no padding if time_t is signed and
    either the compiler lacks support for _Generic or time_t is not one
    of the standard signed integer types.  */
-#if HAVE_GENERIC
+#if HAVE__GENERIC
 # define TIME_T_MIN \
     _Generic((time_t) 0, \
 	     signed char: SCHAR_MIN, short: SHRT_MIN, \
@@ -664,10 +848,23 @@
 		int: INT_MAX, long: LONG_MAX, long long: LLONG_MAX, \
 		default: TIME_T_MAX_NO_PADDING)			    \
      : (time_t) -1)
+enum { SIGNED_PADDING_CHECK_NEEDED
+         = _Generic((time_t) 0,
+		    signed char: false, short: false,
+		    int: false, long: false, long long: false,
+		    default: true) };
 #else
 # define TIME_T_MIN TIME_T_MIN_NO_PADDING
 # define TIME_T_MAX TIME_T_MAX_NO_PADDING
+enum { SIGNED_PADDING_CHECK_NEEDED = true };
 #endif
+/* Try to check the padding assumptions.  Although TIME_T_MAX and the
+   following check can both have undefined behavior on oddball
+   platforms due to shifts exceeding widths of signed integers, these
+   platforms' compilers are likely to diagnose these issues in integer
+   constant expressions, so it shouldn't hurt to check statically.  */
+static_assert(! TYPE_SIGNED(time_t) || ! SIGNED_PADDING_CHECK_NEEDED
+	      || TIME_T_MAX >> (TYPE_BIT(time_t) - 2) == 1);
 
 /*
 ** 302 / 1000 is log10(2.0) rounded up.
@@ -689,21 +886,30 @@
 # define INITIALIZE(x)
 #endif
 
+/* Whether memory access must strictly follow the C standard.
+   If 0, it's OK to read uninitialized storage so long as the value is
+   not relied upon.  Defining it to 0 lets mktime access parts of
+   struct tm that might be uninitialized, as a heuristic when the
+   standard doesn't say what to return and when tm_gmtoff can help
+   mktime likely infer a better value.  */
 #ifndef UNINIT_TRAP
 # define UNINIT_TRAP 0
 #endif
 
 #ifdef DEBUG
-# define UNREACHABLE() abort()
-#elif 4 < __GNUC__ + (5 <= __GNUC_MINOR__)
-# define UNREACHABLE() __builtin_unreachable()
-#elif defined __has_builtin
-# if __has_builtin(__builtin_unreachable)
-#  define UNREACHABLE() __builtin_unreachable()
+# undef unreachable
+# define unreachable() abort()
+#elif !defined unreachable
+# ifdef __has_builtin
+#  if __has_builtin(__builtin_unreachable)
+#   define unreachable() __builtin_unreachable()
+#  endif
+# elif 4 < __GNUC__ + (5 <= __GNUC_MINOR__)
+#  define unreachable() __builtin_unreachable()
 # endif
-#endif
-#ifndef UNREACHABLE
-# define UNREACHABLE() ((void) 0)
+# ifndef unreachable
+#  define unreachable() ((void) 0)
+# endif
 #endif
 
 /*
@@ -725,53 +931,61 @@
 #if HAVE_INCOMPATIBLE_CTIME_R
 #undef asctime_r
 #undef ctime_r
-char *asctime_r(struct tm const *, char *);
+char *asctime_r(struct tm const *restrict, char *restrict);
 char *ctime_r(time_t const *, char *);
 #endif /* HAVE_INCOMPATIBLE_CTIME_R */
 
 /* Handy macros that are independent of tzfile implementation.  */
 
-#define SECSPERMIN	60
-#define MINSPERHOUR	60
-#define HOURSPERDAY	24
-#define DAYSPERWEEK	7
-#define DAYSPERNYEAR	365
-#define DAYSPERLYEAR	366
-#define SECSPERHOUR	(SECSPERMIN * MINSPERHOUR)
-#define SECSPERDAY	((int_fast32_t) SECSPERHOUR * HOURSPERDAY)
-#define MONSPERYEAR	12
+enum {
+  SECSPERMIN = 60,
+  MINSPERHOUR = 60,
+  SECSPERHOUR = SECSPERMIN * MINSPERHOUR,
+  HOURSPERDAY = 24,
+  DAYSPERWEEK = 7,
+  DAYSPERNYEAR = 365,
+  DAYSPERLYEAR = DAYSPERNYEAR + 1,
+  MONSPERYEAR = 12,
+  YEARSPERREPEAT = 400	/* years before a Gregorian repeat */
+};
 
-#define YEARSPERREPEAT		400	/* years before a Gregorian repeat */
+#define SECSPERDAY	((int_fast32_t) SECSPERHOUR * HOURSPERDAY)
+
 #define DAYSPERREPEAT		((int_fast32_t) 400 * 365 + 100 - 4 + 1)
 #define SECSPERREPEAT		((int_fast64_t) DAYSPERREPEAT * SECSPERDAY)
 #define AVGSECSPERYEAR		(SECSPERREPEAT / YEARSPERREPEAT)
 
-#define TM_SUNDAY	0
-#define TM_MONDAY	1
-#define TM_TUESDAY	2
-#define TM_WEDNESDAY	3
-#define TM_THURSDAY	4
-#define TM_FRIDAY	5
-#define TM_SATURDAY	6
+enum {
+  TM_SUNDAY,
+  TM_MONDAY,
+  TM_TUESDAY,
+  TM_WEDNESDAY,
+  TM_THURSDAY,
+  TM_FRIDAY,
+  TM_SATURDAY
+};
 
-#define TM_JANUARY	0
-#define TM_FEBRUARY	1
-#define TM_MARCH	2
-#define TM_APRIL	3
-#define TM_MAY		4
-#define TM_JUNE		5
-#define TM_JULY		6
-#define TM_AUGUST	7
-#define TM_SEPTEMBER	8
-#define TM_OCTOBER	9
-#define TM_NOVEMBER	10
-#define TM_DECEMBER	11
+enum {
+  TM_JANUARY,
+  TM_FEBRUARY,
+  TM_MARCH,
+  TM_APRIL,
+  TM_MAY,
+  TM_JUNE,
+  TM_JULY,
+  TM_AUGUST,
+  TM_SEPTEMBER,
+  TM_OCTOBER,
+  TM_NOVEMBER,
+  TM_DECEMBER
+};
 
-#define TM_YEAR_BASE	1900
-#define TM_WDAY_BASE	TM_MONDAY
-
-#define EPOCH_YEAR	1970
-#define EPOCH_WDAY	TM_THURSDAY
+enum {
+  TM_YEAR_BASE = 1900,
+  TM_WDAY_BASE = TM_MONDAY,
+  EPOCH_YEAR = 1970,
+  EPOCH_WDAY = TM_THURSDAY
+};
 
 #define isleap(y) (((y) % 4) == 0 && (((y) % 100) != 0 || ((y) % 400) == 0))