From b34b46b8806a115b86da3b2b22555ad5bffa89d1 Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Wed, 3 Jan 2024 12:07:14 +0000 Subject: Implement C23 C23 adds a header with various functions and type-generic macros for bit-manipulation of unsigned integers (plus macro defines related to endianness). Implement this header for glibc. The functions have both inline definitions in the header (referenced by macros defined in the header) and copies with external linkage in the library (which are implemented in terms of those macros to avoid duplication). They are documented in the glibc manual. Tests, as well as verifying results for various inputs (of both the macros and the out-of-line functions), verify the types of those results (which showed up a bug in an earlier version with the type-generic macro stdc_has_single_bit wrongly returning a promoted type), that the macros can be used at top level in a source file (so don't use ({})), that they evaluate their arguments exactly once, and that the macros for the type-specific functions have the expected implicit conversions to the relevant argument type. Jakub previously referred to -Wconversion warnings in type-generic macros, so I've included a test with -Wconversion (but the only warnings I saw and fixed from that test were actually in inline functions in the header - not anything coming from use of the type-generic macros themselves). This implementation of the type-generic macros does not handle unsigned __int128, or unsigned _BitInt types with a width other than that of a standard integer type (and C23 doesn't require the header to handle such types either). Support for those types, using the new type-generic built-in functions Jakub's added for GCC 14, can reasonably be added in a followup (along of course with associated tests). This implementation doesn't do anything special to handle C++, or have any tests of functionality in C++ beyond the existing tests that all headers can be compiled in C++ code; it's not clear exactly what form this header should take in C++, but probably not one using macros. DIS ballot comment AT-107 asks for the word "count" to be added to the names of the stdc_leading_zeros, stdc_leading_ones, stdc_trailing_zeros and stdc_trailing_ones functions and macros. I don't think it's likely to be accepted (accepting any technical comments would mean having an FDIS ballot), but if it is accepted at the WG14 meeting (22-26 January in Strasbourg, starting with DIS ballot comment handling) then there would still be time to update glibc for the renaming before the 2.39 release. The new functions and header are placed in the stdlib/ directory in glibc, rather than creating a new toplevel stdbit/ or putting them in string/ alongside ffs. Tested for x86_64 and x86. --- manual/Makefile | 2 +- manual/arith.texi | 2 +- manual/stdbit.texi | 206 +++++++++++++++++++++++++++++++++++++++++++++++++++++ manual/time.texi | 2 +- 4 files changed, 209 insertions(+), 3 deletions(-) create mode 100644 manual/stdbit.texi (limited to 'manual') diff --git a/manual/Makefile b/manual/Makefile index 877e568bbe..b5fda4a7ae 100644 --- a/manual/Makefile +++ b/manual/Makefile @@ -36,7 +36,7 @@ endif chapters = $(addsuffix .texi, \ intro errno memory ctype string charset locale \ message search pattern io stdio llio filesys \ - pipe socket terminal syslog math arith time \ + pipe socket terminal syslog math arith stdbit time \ resource setjmp signal startup process ipc job \ nss users sysinfo conf crypt debug threads \ dynlink probes tunables) diff --git a/manual/arith.texi b/manual/arith.texi index be24c20493..2b99cd8389 100644 --- a/manual/arith.texi +++ b/manual/arith.texi @@ -1,4 +1,4 @@ -@node Arithmetic, Date and Time, Mathematics, Top +@node Arithmetic, Bit Manipulation, Mathematics, Top @c %MENU% Low level arithmetic functions @chapter Arithmetic Functions diff --git a/manual/stdbit.texi b/manual/stdbit.texi new file mode 100644 index 0000000000..fe41c671d8 --- /dev/null +++ b/manual/stdbit.texi @@ -0,0 +1,206 @@ +@node Bit Manipulation, Date and Time, Arithmetic, Top +@c %MENU% Bit manipulation +@chapter Bit Manipulation + +This chapter contains information about functions and macros for +determining the endianness of integer types and manipulating the bits +of unsigned integers. These functions and macros are from ISO C2X and +are declared in the header file @file{stdbit.h}. + +The following macros describe the endianness of integer types. They +have values that are integer constant expressions. + +@defmac __STDC_ENDIAN_LITTLE__ +This macro represents little-endian storage. +@end defmac + +@defmac __STDC_ENDIAN_BIG__ +This macro represents big-endian storage. +@end defmac + +@defmac __STDC_ENDIAN_NATIVE__ +This macro equals @code{__STDC_ENDIAN_LITTLE__} if integer types are +stored in memory in little-endian format, and equals +@code{__STDC_ENDIAN_BIG__} if integer types are stored in memory in +big-endian format. +@end defmac + +The following functions manipulate the bits of unsigned integers. +Each function family has functions for the types @code{unsigned char}, +@code{unsigned short}, @code{unsigned int}, @code{unsigned long int} +and @code{unsigned long long int}. In addition, there is a +corresponding type-generic macro (not listed below), named the same as +the functions but without any suffix such as @samp{_uc}. The +type-generic macro can only be used with an argument of an unsigned +integer type with a width of 8, 16, 32 or 64 bits. + +@deftypefun {unsigned int} stdc_leading_zeros_uc (unsigned char @var{x}) +@deftypefunx {unsigned int} stdc_leading_zeros_us (unsigned short @var{x}) +@deftypefunx {unsigned int} stdc_leading_zeros_ui (unsigned int @var{x}) +@deftypefunx {unsigned int} stdc_leading_zeros_ul (unsigned long int @var{x}) +@deftypefunx {unsigned int} stdc_leading_zeros_ull (unsigned long long int @var{x}) +@standards{C2X, stdbit.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +The @code{stdc_leading_zeros} functions count the number of leading +(most significant) zero bits in @var{x}, starting from the most +significant bit of the argument type. If @var{x} is zero, they return +the width of @var{x} in bits. +@end deftypefun + +@deftypefun {unsigned int} stdc_leading_ones_uc (unsigned char @var{x}) +@deftypefunx {unsigned int} stdc_leading_ones_us (unsigned short @var{x}) +@deftypefunx {unsigned int} stdc_leading_ones_ui (unsigned int @var{x}) +@deftypefunx {unsigned int} stdc_leading_ones_ul (unsigned long int @var{x}) +@deftypefunx {unsigned int} stdc_leading_ones_ull (unsigned long long int @var{x}) +@standards{C2X, stdbit.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +The @code{stdc_leading_ones} functions count the number of leading +(most significant) one bits in @var{x}, starting from the most +significant bit of the argument type. +@end deftypefun + +@deftypefun {unsigned int} stdc_trailing_zeros_uc (unsigned char @var{x}) +@deftypefunx {unsigned int} stdc_trailing_zeros_us (unsigned short @var{x}) +@deftypefunx {unsigned int} stdc_trailing_zeros_ui (unsigned int @var{x}) +@deftypefunx {unsigned int} stdc_trailing_zeros_ul (unsigned long int @var{x}) +@deftypefunx {unsigned int} stdc_trailing_zeros_ull (unsigned long long int @var{x}) +@standards{C2X, stdbit.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +The @code{stdc_trailing_zeros} functions count the number of trailing +(least significant) zero bits in @var{x}, starting from the least +significant bit of the argument type. If @var{x} is zero, they return +the width of @var{x} in bits. +@end deftypefun + +@deftypefun {unsigned int} stdc_trailing_ones_uc (unsigned char @var{x}) +@deftypefunx {unsigned int} stdc_trailing_ones_us (unsigned short @var{x}) +@deftypefunx {unsigned int} stdc_trailing_ones_ui (unsigned int @var{x}) +@deftypefunx {unsigned int} stdc_trailing_ones_ul (unsigned long int @var{x}) +@deftypefunx {unsigned int} stdc_trailing_ones_ull (unsigned long long int @var{x}) +@standards{C2X, stdbit.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +The @code{stdc_trailing_ones} functions count the number of trailing +(least significant) one bits in @var{x}, starting from the least +significant bit of the argument type. +@end deftypefun + +@deftypefun {unsigned int} stdc_first_leading_zero_uc (unsigned char @var{x}) +@deftypefunx {unsigned int} stdc_first_leading_zero_us (unsigned short @var{x}) +@deftypefunx {unsigned int} stdc_first_leading_zero_ui (unsigned int @var{x}) +@deftypefunx {unsigned int} stdc_first_leading_zero_ul (unsigned long int @var{x}) +@deftypefunx {unsigned int} stdc_first_leading_zero_ull (unsigned long long int @var{x}) +@standards{C2X, stdbit.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +The @code{stdc_first_leading_zero} functions return the position of +the most significant zero bit in @var{x}, counting from the most +significant bit of @var{x} as 1, or zero if there is no zero bit in +@var{x}. +@end deftypefun + +@deftypefun {unsigned int} stdc_first_leading_one_uc (unsigned char @var{x}) +@deftypefunx {unsigned int} stdc_first_leading_one_us (unsigned short @var{x}) +@deftypefunx {unsigned int} stdc_first_leading_one_ui (unsigned int @var{x}) +@deftypefunx {unsigned int} stdc_first_leading_one_ul (unsigned long int @var{x}) +@deftypefunx {unsigned int} stdc_first_leading_one_ull (unsigned long long int @var{x}) +@standards{C2X, stdbit.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +The @code{stdc_first_leading_one} functions return the position of the +most significant one bit in @var{x}, counting from the most +significant bit of @var{x} as 1, or zero if there is no one bit in +@var{x}. +@end deftypefun + +@deftypefun {unsigned int} stdc_first_trailing_zero_uc (unsigned char @var{x}) +@deftypefunx {unsigned int} stdc_first_trailing_zero_us (unsigned short @var{x}) +@deftypefunx {unsigned int} stdc_first_trailing_zero_ui (unsigned int @var{x}) +@deftypefunx {unsigned int} stdc_first_trailing_zero_ul (unsigned long int @var{x}) +@deftypefunx {unsigned int} stdc_first_trailing_zero_ull (unsigned long long int @var{x}) +@standards{C2X, stdbit.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +The @code{stdc_first_trailing_zero} functions return the position of +the least significant zero bit in @var{x}, counting from the least +significant bit of @var{x} as 1, or zero if there is no zero bit in +@var{x}. +@end deftypefun + +@deftypefun {unsigned int} stdc_first_trailing_one_uc (unsigned char @var{x}) +@deftypefunx {unsigned int} stdc_first_trailing_one_us (unsigned short @var{x}) +@deftypefunx {unsigned int} stdc_first_trailing_one_ui (unsigned int @var{x}) +@deftypefunx {unsigned int} stdc_first_trailing_one_ul (unsigned long int @var{x}) +@deftypefunx {unsigned int} stdc_first_trailing_one_ull (unsigned long long int @var{x}) +@standards{C2X, stdbit.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +The @code{stdc_first_trailing_one} functions return the position of +the least significant one bit in @var{x}, counting from the least +significant bit of @var{x} as 1, or zero if there is no one bit in +@var{x}. +@end deftypefun + +@deftypefun {unsigned int} stdc_count_zeros_uc (unsigned char @var{x}) +@deftypefunx {unsigned int} stdc_count_zeros_us (unsigned short @var{x}) +@deftypefunx {unsigned int} stdc_count_zeros_ui (unsigned int @var{x}) +@deftypefunx {unsigned int} stdc_count_zeros_ul (unsigned long int @var{x}) +@deftypefunx {unsigned int} stdc_count_zeros_ull (unsigned long long int @var{x}) +@standards{C2X, stdbit.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +The @code{stdc_count_zeros} functions count the number of zero bits in +@var{x}. +@end deftypefun + +@deftypefun {unsigned int} stdc_count_ones_uc (unsigned char @var{x}) +@deftypefunx {unsigned int} stdc_count_ones_us (unsigned short @var{x}) +@deftypefunx {unsigned int} stdc_count_ones_ui (unsigned int @var{x}) +@deftypefunx {unsigned int} stdc_count_ones_ul (unsigned long int @var{x}) +@deftypefunx {unsigned int} stdc_count_ones_ull (unsigned long long int @var{x}) +@standards{C2X, stdbit.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +The @code{stdc_count_ones} functions count the number of one bits in +@var{x}. +@end deftypefun + +@deftypefun {_Bool} stdc_has_single_bit_uc (unsigned char @var{x}) +@deftypefunx {_Bool} stdc_has_single_bit_us (unsigned short @var{x}) +@deftypefunx {_Bool} stdc_has_single_bit_ui (unsigned int @var{x}) +@deftypefunx {_Bool} stdc_has_single_bit_ul (unsigned long int @var{x}) +@deftypefunx {_Bool} stdc_has_single_bit_ull (unsigned long long int @var{x}) +@standards{C2X, stdbit.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +The @code{stdc_has_single_bit} functions return whether @var{x} has +exactly one bit set to one. +@end deftypefun + +@deftypefun {unsigned int} stdc_bit_width_uc (unsigned char @var{x}) +@deftypefunx {unsigned int} stdc_bit_width_us (unsigned short @var{x}) +@deftypefunx {unsigned int} stdc_bit_width_ui (unsigned int @var{x}) +@deftypefunx {unsigned int} stdc_bit_width_ul (unsigned long int @var{x}) +@deftypefunx {unsigned int} stdc_bit_width_ull (unsigned long long int @var{x}) +@standards{C2X, stdbit.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +The @code{stdc_bit_width} functions return the minimum number of bits +needed to store @var{x}, not counting leading zero bits. If @var{x} +is zero, they return zero. +@end deftypefun + +@deftypefun {unsigned char} stdc_bit_floor_uc (unsigned char @var{x}) +@deftypefunx {unsigned short} stdc_bit_floor_us (unsigned short @var{x}) +@deftypefunx {unsigned int} stdc_bit_floor_ui (unsigned int @var{x}) +@deftypefunx {unsigned long int} stdc_bit_floor_ul (unsigned long int @var{x}) +@deftypefunx {unsigned long long int} stdc_bit_floor_ull (unsigned long long int @var{x}) +@standards{C2X, stdbit.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +The @code{stdc_bit_floor} functions return the largest integer power +of two that is less than or equal to @var{x}. If @var{x} is zero, +they return zero. +@end deftypefun + +@deftypefun {unsigned char} stdc_bit_ceil_uc (unsigned char @var{x}) +@deftypefunx {unsigned short} stdc_bit_ceil_us (unsigned short @var{x}) +@deftypefunx {unsigned int} stdc_bit_ceil_ui (unsigned int @var{x}) +@deftypefunx {unsigned long int} stdc_bit_ceil_ul (unsigned long int @var{x}) +@deftypefunx {unsigned long long int} stdc_bit_ceil_ull (unsigned long long int @var{x}) +@standards{C2X, stdbit.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +The @code{stdc_bit_ceil} functions return the smallest integer power +of two that is greater than or equal to @var{x}. If this cannot be +represented in the return type, they return zero. +@end deftypefun diff --git a/manual/time.texi b/manual/time.texi index d661d55d40..7d9efc7c6f 100644 --- a/manual/time.texi +++ b/manual/time.texi @@ -1,4 +1,4 @@ -@node Date and Time, Resource Usage And Limitation, Arithmetic, Top +@node Date and Time, Resource Usage And Limitation, Bit Manipulation, Top @c %MENU% Functions for getting the date and time and formatting them nicely @chapter Date and Time -- cgit 1.4.1