The threshold value at which powf overflows depends on the rounding mode
and the current check did not take this into account. So when the result
was rounded away from zero it could become infinity without setting
errno to ERANGE.
Example: pow(0x1.7ac7cp+5, 23) is 0x1.fffffep+127 + 0.1633ulp
If the result goes above 0x1.fffffep+127 + 0.5ulp then errno is set,
which is fine in nearest rounding mode, but
powf(0x1.7ac7cp+5, 23) is inf in upward rounding mode
powf(-0x1.7ac7cp+5, 23) is -inf in downward rounding mode
and the previous implementation did not set errno in these cases.
The fix tries to avoid affecting the common code path or calling a
function that may introduce a stack frame, so float arithmetics is used
to check the rounding mode and the threshold is selected accordingly.
[BZ #23961]
* math/auto-libm-test-in: Add new test case.
* math/auto-libm-test-out-pow: Regenerated.
* sysdeps/ieee754/flt-32/e_powf.c (__powf): Fix overflow check.
Bug 21112 reports a case where powf is substantially inaccurate. This
results from a multiplication where cp_h*p_h is required to be exact,
and p_h is masked to have only 12 leading nonzero bits in its
mantissa, but the value of cp_h has the 13th bit nonzero, leading to
inexact multiplication results in some cases that can result in large
errors in the final result of powf. This patch fixes this by using a
value of cp_h correctly rounded to nearest to 12 bits, with a
corresponding updated value of cp_l.
Tested for x86_64 and x86.
[BZ #21112]
* sysdeps/ieee754/flt-32/e_powf.c (cp_h): Use value with trailing
12 bits zero.
(cp_l): Update for new value of cp_h.
* math/auto-libm-test-in: Add another test of pow.
* math/auto-libm-test-out-pow: Regenerated.
math/auto-libm-test-out is, at over 30 MB, by far the largest file in
the glibc source tree. This patch splits it by function, so reducing
it to auto-libm-test-out-<func> files that are all under 5 MB in size.
This is preliminary to splitting up libm-test.inc as well so that each
function's tests can also be processed separately by
gen-libm-test.pl. As a preliminary patch it doesn't actually
implement that step; rather, all the separate files get concatenated
by the Makefile to produce the monolithic auto-libm-test-out file
again as an input to gen-libm-test.pl. (The concatentation is
identical to the file in the source tree before this patch.)
Even this preliminary step, however, is of use independent of
splitting up libm-test.inc: some tests for csin and csinh have not
been moved to auto-libm-test-in because they result in
auto-libm-test-out generation taking several minutes rather than a few
seconds (all released MPC versions are very slow for certain sin /
sinh inputs; there are some old improvements in MPC mainline which
should eventually become MPC 1.1, but the complex inverse trig and
hyperbolic functions are slow even in MPC mainline and have yet to be
moved to auto-libm-test-in at all), and it seems much more reasonable
to add such inputs to auto-libm-test-in when it will only slow down
regeneration for particular functions than when it will slow down
regeneration globally.
gen-auto-libm-tests still parses the whole input file, but only
generates output for the requested function. This ensures bad syntax
in the file is always detected, and parsing the whole file is quick;
it's output generation that is comparatively slow for some functions.
Tested for x86_64.
* math/gen-auto-libm-tests.c: Update comment about use of program.
(generate_output): Add argument FUNCTION.
(main): Require extra argument. Pass function name to
generate_output.
* math/Makefile (generated): Add auto-libm-test-out.
(libm-test-funcs-auto): New variable.
(auto-libm-test-out-files): New variable.
($(objpfx)libm-test.c): Depend on $(auto-libm-test-out-files).
Concatenate those files to form $(objpfx)auto-libm-test-out and
use it as input to gen-libm-test.pl.
* math/README.libm-test: Update.
* math/auto-libm-test-out: Remove.
* math/auto-libm-test-out-acos: New generated file.
* math/auto-libm-test-out-acosh: Likewise.
* math/auto-libm-test-out-asin: Likewise.
* math/auto-libm-test-out-asinh: Likewise.
* math/auto-libm-test-out-atan: Likewise.
* math/auto-libm-test-out-atan2: Likewise.
* math/auto-libm-test-out-atanh: Likewise.
* math/auto-libm-test-out-cabs: Likewise.
* math/auto-libm-test-out-carg: Likewise.
* math/auto-libm-test-out-cbrt: Likewise.
* math/auto-libm-test-out-ccos: Likewise.
* math/auto-libm-test-out-ccosh: Likewise.
* math/auto-libm-test-out-cexp: Likewise.
* math/auto-libm-test-out-clog: Likewise.
* math/auto-libm-test-out-clog10: Likewise.
* math/auto-libm-test-out-cos: Likewise.
* math/auto-libm-test-out-cosh: Likewise.
* math/auto-libm-test-out-cpow: Likewise.
* math/auto-libm-test-out-csin: Likewise.
* math/auto-libm-test-out-csinh: Likewise.
* math/auto-libm-test-out-csqrt: Likewise.
* math/auto-libm-test-out-ctan: Likewise.
* math/auto-libm-test-out-ctanh: Likewise.
* math/auto-libm-test-out-erf: Likewise.
* math/auto-libm-test-out-erfc: Likewise.
* math/auto-libm-test-out-exp: Likewise.
* math/auto-libm-test-out-exp10: Likewise.
* math/auto-libm-test-out-exp2: Likewise.
* math/auto-libm-test-out-expm1: Likewise.
* math/auto-libm-test-out-fma: Likewise.
* math/auto-libm-test-out-hypot: Likewise.
* math/auto-libm-test-out-j0: Likewise.
* math/auto-libm-test-out-j1: Likewise.
* math/auto-libm-test-out-jn: Likewise.
* math/auto-libm-test-out-lgamma: Likewise.
* math/auto-libm-test-out-log: Likewise.
* math/auto-libm-test-out-log10: Likewise.
* math/auto-libm-test-out-log1p: Likewise.
* math/auto-libm-test-out-log2: Likewise.
* math/auto-libm-test-out-pow: Likewise.
* math/auto-libm-test-out-sin: Likewise.
* math/auto-libm-test-out-sincos: Likewise.
* math/auto-libm-test-out-sinh: Likewise.
* math/auto-libm-test-out-sqrt: Likewise.
* math/auto-libm-test-out-tan: Likewise.
* math/auto-libm-test-out-tanh: Likewise.
* math/auto-libm-test-out-tgamma: Likewise.
* math/auto-libm-test-out-y0: Likewise.
* math/auto-libm-test-out-y1: Likewise.
* math/auto-libm-test-out-yn: Likewise.
