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ISO C2X has made some changes to the handling of feature test macros related to features from the floating-point TSes, and to exactly what such features are present in what headers, that require corresponding changes in glibc. * For the few features that were controlled by __STDC_WANT_IEC_60559_BFP_EXT__ (and the corresponding DFP macro) in C2X, there is now instead a new feature test macro __STDC_WANT_IEC_60559_EXT__ covering both binary and decimal FP. This controls CR_DECIMAL_DIG in <float.h> (provided by GCC; I implemented support for the new feature test macro for GCC 11) and the totalorder and payload functions in <math.h>. C2X no longer says anything about __STDC_WANT_IEC_60559_BFP_EXT__ (so it's appropriate for that macro to continue to enable exactly the features from TS 18661-1). * The SNAN macros for each floating-point type have moved to <float.h> (and been renamed in the process). Thus, the copies in <math.h> should only be defined for __STDC_WANT_IEC_60559_BFP_EXT__, not for C2X. * The fmaxmag and fminmag functions have been removed (replaced by new functions for the new min/max operations in IEEE 754-2019). Thus those should also only be declared for __STDC_WANT_IEC_60559_BFP_EXT__. * The _FloatN / _FloatNx handling for the last two points in glibc is trickier, since __STDC_WANT_IEC_60559_TYPES_EXT__ is still in C2X (the integration of TS 18661-3 as an Annex, that is, which hasn't yet been merged into the C standard git repository but has been accepted by WG14), so C2X with that macro should not declare some things that are declared for older standards with that macro. The approach taken here is to provide the declarations (when __STDC_WANT_IEC_60559_TYPES_EXT__ is enabled) only when (defined __USE_GNU || !__GLIBC_USE (ISOC2X)), so if C2X features are enabled then those declarations (that are only in TS 18661-3 and not in C2X) will only be provided if _GNU_SOURCE is defined as well. Thus _GNU_SOURCE remains a superset of the TS features as well as of C2X. Some other somewhat related changes in C2X are not addressed here. There's an open proposal not to include the fmin and fmax functions for the _FloatN / _FloatNx types, given the new min/max operations, which could be handled like the previous point if adopted. And the fromfp functions have been changed to return a result in floating type rather than intmax_t / uintmax_t; my inclination there is to treat that like that change of totalorder type (new symbol versions etc. for the ABI change; old versions become compat symbols and are no longer supported as an API). Tested for x86_64 and x86.
README for libm-test math test suite
====================================
The libm-test math test suite tests a number of function points of
math functions in the GNU C library. The following sections contain a
brief overview. Please note that the test drivers and the Python
script "gen-libm-test.py" have some options. A full list of options
is available with --help (for the test drivers) and -h for
"gen-libm-test.py".
What is tested?
===============
The tests just evaluate the functions at specified points and compare
the results with precomputed values and the requirements of the ISO
C99 standard.
Besides testing the special values mandated by IEEE 754 (infinities,
NaNs and minus zero), some more or less random values are tested.
Files that are part of libm-test
================================
The main files are "libm-test-<func>.inc". They are independent of
the target platform and the specific real floating type and format and
contain placeholder test "templates" for math functions defined in
libm. These files, along with generated files named
"auto-libm-test-out-<func>", are preprocessed by the Python script
"gen-libm-test.py" to expand the templates and produce a set of test
cases for each math function that are specific to the target platform
but still independent of the real floating type. The results of the
processing are "libm-test-<func>.c" and a file "libm-test-ulps.h" with
platform specific deltas by which the actual math function results may
deviate from the expected results and still be considered correct.
The test drivers "test-double-<func>.c", "test-float-<func>.c", and
"test-ldouble-<func>.c", generated by the Makefile, test the normal
double, float and long double implementation of libm. Each driver
selects the desired real floating type to exercise the math functions
to test with (float, double, or long double) by defining a small set
of macros just before including the generic "libm-test.c" file. Each
driver is compiled into a single executable test program with the
corresponding name.
As mentioned above, the "gen-libm-test.py" script looks for a file
named "libm-test-ulps" in the platform specific sysdep directory (or
its fpu or nofpu subdirectory) and for each variant (real floating
type and rounding mode) of every tested function reads from it the
maximum difference expressed as Units of Least Precision (ULP) the
actual result of the function may deviate from the expected result
before it's considered incorrect.
The "auto-libm-test-out-<func>" files contain sets of test cases to
exercise, the conditions under which to exercise each, and the
expected results. The files are generated by the
"gen-auto-libm-tests" program from the "auto-libm-test-in" file. See
the comments in gen-auto-libm-tests.c for details about the content
and format of the -in and -out files.
How can I generate "libm-test-ulps"?
====================================
To automatically generate a new "libm-test-ulps" run "make regen-ulps".
This generates the file "math/NewUlps" in the build directory. The file
contains the sorted results of all the tests. You can use the "NewUlps"
file as the machine's updated "libm-test-ulps" file. Copy "NewUlps" to
"libm-test-ulps" in the appropriate machine sysdep directory. Verify
the changes, post your patch, and check it in after review.
To manually generate a new "libm-test-ulps" file, first remove "ULPs"
file in the current directory, then you can execute for example:
./testrun.sh math/test-double -u --ignore-max-ulp=yes
This generates a file "ULPs" with all double ULPs in it, ignoring any
previously calculated ULPs, and running with the newly built dynamic
loader and math library (assumes you didn't install your build). Now
generate the ULPs for all other formats, the tests will be appending the
data to the "ULPs" file. As final step run "gen-libm-test.py" with the
file as input and ask to generate a pretty printed output in the file
"NewUlps":
gen-libm-test.py -u ULPs -n NewUlps
Copy "NewUlps" to "libm-test-ulps" in the appropriate machine sysdep
directory.
Note that the test drivers have an option "-u" to output an unsorted
list of all epsilons that the functions have. The output can be read
in directly but it's better to pretty print it first.
"gen-libm-test.py" has an option to generate a pretty-printed and
sorted new ULPs file from the output of the test drivers.
Contents of libm-test-ulps
==========================
Since libm-test-ulps can be generated automatically, just a few notes.
The file contains lines for maximal errors of single functions, like:
Function "yn":
double: 6
The keywords are float, double, and ldouble.
Adding tests to libm-test-<func>.inc
====================================
The tests are evaluated by a set of special test macros. The macros
start with "TEST_" followed by a specification the input values, an
underscore and a specification of the output values. As an example,
the test macro for a function with input of type FLOAT (FLOAT is
either float, double, long double) and output of type FLOAT is
"TEST_f_f". The macro's parameter are the name of the function, the
input parameter, output parameter and optionally one exception
parameter.
The accepted parameter types are:
- "f" for FLOAT
- "j" for long double.
- "a" for ARG_FLOAT, the argument type for narrowing functions.
- "b" for boolean - just tests if the output parameter evaluates to 0
or 1 (only for output).
- "c" for complex. This parameter needs two values, first the real,
then the imaginary part.
- "i" for int.
- "l" for long int.
- "L" for long long int.
- "u" for unsigned int.
- "M" for intmax_t.
- "U" for uintmax_t.
- "p" for an argument (described in the previous character) passed
through a pointer rather than directly.
- "F" for the address of a FLOAT (only as input parameter)
- "I" for the address of an int (only as input parameter)
- "1" for an additional output (either output through a pointer passed
as an argument, or to a global variable such as signgam).
How to read the test output
===========================
Running each test on its own at the default level of verbosity will
print on stdout a line describing the implementation of math functions
exercised by the test (float, double, or long double). This is then
followed by the details of test failures (if any). The output concludes
by a summary listing the number of test cases exercised and the number
of test failures uncovered.
For each test failure (and for each test case at higher levels of
verbosity), the output contains the name of the function under test
and its arguments or conditions that triggered the failure. Note
that the name of the function in the output need not correspond
exactly to the name of the math function actually invoked. For example,
the output will refer to the "acos" function even if the actual function
under test is acosf (for the float version) or acosl (for the long
double version). Also note that the function arguments may be shown
in either the decimal or the hexadecimal floating point format which
may or may not correspond to the format used in the auto-libm-test-in
file. Besides the name of the function, for each test failure the
output contains the actual and expected results and the difference
between the two, printed in both the decimal and hexadecimal
floating point format, and the ULP and maximum ULP for the test
case.