mirror of
git://sourceware.org/git/glibc.git
synced 2025-04-12 14:21:18 +08:00
72d839a42f
The dbl-64 implementation of __ieee754_pow returns a NaN for pow (qNaN, 0) when it should return 1. Normally this is covered up by the wrappers ending up calling __kernel_standard which fixes up the result for this case, but for -lieee the wrappers are bypassed and the bad result gets through as a return value. Now, the wrappers fixing this are dealing with variant error handling that wants a result of NaN for pow (qNaN, 0), and only ever call __kernel_standard for this case if NaN resulted from __ieee754_pow. This leads to a question of whether the dbl-64 code might be deliberately returning NaN in order to use those code paths. However, I can find no sign that this is deliberate. If it were deliberate one would expect other implementations to do the same, and would expect the return of NaN to be very old, but it appears it came in by accident when the present e_pow.c implementation replaced an fdlibm implementation in 2001. So it appears to be unintended that this path through the pow wrapper could be used at all. So this patch fixes the implementation to return 1 in this case as expected. This is consistent with all the other implementations. The relevant path through the wrappers is now unreachable, so is removed (which is the main motivation of this patch: to avoid that path becoming accidentally reachable when implementing TS 18661-1 semantics that pow (sNaN, 0) should return qNaN with "invalid" raised). Another path that would require __ieee754_pow (0, 0) to return 0 is also unreachable (as all implementations return 1, in accordance with C99 semantics), so is removed as well. Note: we don't have anything set up to test -lieee, which in any case is obsolescent (at some point we should remove the ability for new programs to access _LIB_VERSION or define matherr and have it called by glibc). So testing will be implicit through sNaN tests added when making sNaN inputs work correctly for pow functions. Tested for x86_64 and x86. [BZ #20919] * sysdeps/ieee754/dbl-64/e_pow.c (__ieee754_pow): Do not return NaN first argument when raised to power 0. * math/w_pow.c (__pow): Do not check for NaN or zero results from raising to power zero. * math/w_powf.c (__powf): Likewise. * math/w_powl.c (__powl): Likewise. * sysdeps/ieee754/k_standard.c (__kernel_standard): Do not handle pow (0, 0) or pow (NaN, 0).
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 Perl script
"gen-libm-test.pl" have some options. A full list of options is
available with --help (for the test drivers) and -h for
"gen-libm-test.pl".
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 file is "libm-test.inc". It is independent of the target
platform and the specific real floating type and format and contains
placeholder test "templates" for math functions defined in libm.
The file, along with a generated file named "auto-libm-test-out",
is preprocessed by the Perl script "gen-libm-test.pl" 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.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.c", "test-float.c", and "test-ldouble.c"
test the normal double, float and long double implementation of libm.
The test drivers with an 'i' in their name ("test-idouble.c",
"test-ifloat.c", and "test-ildoubl.c") test the corresponding inline
functions (where available - otherwise they also test the real
functions in 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 also either defines or
undefines the __NO_MATH_INLINES macro just before including
"libm-test.c" to select either the real or inline functions,
respectively. Each driver is compiled into a single executable test
program with the corresponding name.
As mentioned above, the "gen-libm-test.pl" 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" file contains sets of test cases to exercise,
the conditions under which to exercise each, and the expected results.
The file is 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.pl" with the
file as input and ask to generate a pretty printed output in the file
"NewUlps":
gen-libm-test.pl -u ULPs -n
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.pl" 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":
idouble: 6
The keywords are float, ifloat, double, idouble, ldouble and ildouble
(the prefix i stands for inline).
Adding tests to libm-test.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
- "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.
- "F" for the address of a FLOAT (only as input parameter)
- "I" for the address of an int (only as input parameter)
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), along with
whether the inline set has been selected, regardless of whether or
not any inline functions actually exist. 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.