mirror of
git://sourceware.org/git/glibc.git
synced 2025-03-31 14:01:18 +08:00
63716ab270
TS 18661-1 defines libm functions that carry out an operation (+ - * / sqrt fma) on their arguments and return a result rounded to a (usually) narrower type, as if the original result were computed to infinite precision and then rounded directly to the result type without any intermediate rounding to the argument type. For example, fadd, faddl and daddl for addition. These are the last remaining TS 18661-1 functions left to be added to glibc. TS 18661-3 extends this to corresponding functions for _FloatN and _FloatNx types. As functions parametrized by two rather than one varying floating-point types, these functions require infrastructure in glibc that was not required for previous libm functions. This patch provides such infrastructure - excluding test support, and actual function implementations, which will be in subsequent patches. Declaring the functions uses a header bits/mathcalls-narrow.h, which is included many times, for each relevant pair of types. This will end up containing macro calls of the form __MATHCALL_NARROW (__MATHCALL_NAME (add), __MATHCALL_REDIR_NAME (add), 2); for each family of narrowing functions. (The structure of this macro call, with the calls to __MATHCALL_NAME and __MATHCALL_REDIR_NAME there rather than in the definition of __MATHCALL_NARROW, arises from the names such as "add" *not* themselves being reserved identifiers - meaning it's necessary to avoid any indirection that would result in a user-defined "add" macro being expanded.) Whereas for existing functions declaring long double functions is disabled if _LIBC in the case where they alias double functions, to facilitate defining the long double functions as aliases of the double ones, there is no such logic for the narrowing functions in this patch. Rather, the files defining such functions are expected to use #define to hide the original declarations of the alias names, to avoid errors about defining aliases with incompatible types. math/Makefile support is added for building the functions (listed in libm-narrow-fns, currently empty) for all relevant pairs of types. An internal header math-narrow.h is added for macros shared between multiple function implementations - currently a ROUND_TO_ODD macro to facilitate writing functions using the round-to-odd implementation approach, and alias macros to create all the required function aliases. libc_feholdexcept_setroundf128 and libc_feupdateenv_testf128 are added for use when required (only for x86_64). float128_private.h support is added for ldbl-128 narrowing functions to be used for _Float128. Certain things are specifically omitted from this patch and the immediate followups. tgmath.h support is deferred; there remain unresolved questions about how the type-generic macros for these functions are supposed to work, especially in the case of arguments of integer type. The math.h / bits/mathcalls-narrow.h logic, and the logic for determining what functions / aliases to define, will need some adjustments to support the sqrt and fma functions, where e.g. f32xsqrtf64 can just be an alias for sqrt rather than a separate function. TS 18661-1 defines FP_FAST_* macros but no support is included for defining them (they won't in general be true without architecture-specific optimized function versions). For each of the function groups (add sub mul div sqrt fma) there are always six functions present (e.g. fadd, faddl, daddl, f32addf64, f32addf32x, f32xaddf64). When _Float64x and _Float128 are supported, there are seven more (e.g. f32addf64x, f32addf128, f64addf64x, f64addf128, f32xaddf64x, f32xaddf128, f64xaddf128). In addition, in the ldbl-opt case there are function names such as __nldbl_daddl (an alias for f32xaddf64, which is not a reserved name in TS 18661-1, only in TS 18661-3), for calls to daddl to be mapped to in the -mlong-double-64 case. (Calls to faddl just get mapped to fadd, and for sqrt and fma there won't be __nldbl_* functions because dsqrtl and dfmal can just be mapped to sqrt and fma with -mlong-double-64.) While there are six or thirteen functions present in each group (plus __nldbl_* names only as an ABI, not an API), not all are distinct; they fall in various groups of aliases. There are two distinct versions built if long double has the same format as double; four if they have distinct formats but there is no _Float64x or _Float128 support; five if long double has binary128 format; seven when _Float128 is distinct from long double. Architecture-specific optimized versions are possible, but not included in my patches. For example, IA64 generally supports narrowing the result of most floating-point instructions; Power ISA 2.07 (POWER8) supports double values as arguments to float instructions, with the results narrowed as expected; Power ISA 3 (POWER9) supports round-to-odd for float128 instructions, so meaning that approach can be used without needing to set and restore the rounding mode and test "inexact". I intend to leave any such optimized versions to the architecture maintainers. Generally in such cases it would also make sense for calls to these functions to be expanded inline (given -fno-math-errno); I put a suggestion for TS 18661-1 built-in functions at <https://gcc.gnu.org/wiki/SummerOfCode>. Tested for x86_64 (this patch in isolation, as well as testing for various configurations in conjunction with further patches). * math/bits/mathcalls-narrow.h: New file. * include/bits/mathcalls-narrow.h: Likewise. * math/math-narrow.h: Likewise. * math/math.h (__MATHCALL_NARROW_ARGS_1): New macro. (__MATHCALL_NARROW_ARGS_2): Likewise. (__MATHCALL_NARROW_ARGS_3): Likewise. (__MATHCALL_NARROW_NORMAL): Likewise. (__MATHCALL_NARROW_REDIR): Likewise. (__MATHCALL_NARROW): Likewise. [__GLIBC_USE (IEC_60559_BFP_EXT)]: Repeatedly include <bits/mathcalls-narrow.h> with _Mret_, _Marg_ and __MATHCALL_NAME defined. [__GLIBC_USE (IEC_60559_TYPES_EXT)]: Likewise. * math/Makefile (headers): Add bits/mathcalls-narrow.h. (libm-narrow-fns): New variable. (libm-narrow-types-basic): Likewise. (libm-narrow-types-ldouble-yes): Likewise. (libm-narrow-types-float128-yes): Likewise. (libm-narrow-types-float128-alias-yes): Likewise. (libm-narrow-types): Likewise. (libm-routines): Add narrowing functions. * sysdeps/i386/fpu/fenv_private.h [__x86_64__] (libc_feholdexcept_setroundf128): New macro. [__x86_64__] (libc_feupdateenv_testf128): Likewise. * sysdeps/ieee754/float128/float128_private.h: Include <math/math-narrow.h>. [libc_feholdexcept_setroundf128] (libc_feholdexcept_setroundl): Undefine and redefine. [libc_feupdateenv_testf128] (libc_feupdateenv_testl): Likewise. (libm_alias_float_ldouble): Undefine and redefine. (libm_alias_double_ldouble): Likewise.
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 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 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-<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. The test
drivers with an 'i' in their name ("test-idouble-<func>.c",
"test-ifloat-<func>.c", and "test-ildoubl-<func>.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-<func>.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-<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.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 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.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-<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.
- "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), 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.