mirror of
https://sourceware.org/git/glibc.git
synced 2024-09-18 23:49:57 +00:00
79c52daf47
C23 adds various <math.h> function families originally defined in TS 18661-4. Add the log2p1 functions (log2(1+x): like log1p, but for base-2 logarithms). This illustrates the intended structure of implementations of all these function families: define them initially with a type-generic template implementation. If someone wishes to add type-specific implementations, it is likely such implementations can be both faster and more accurate than the type-generic one and can then override it for types for which they are implemented (adding benchmarks would be desirable in such cases to demonstrate that a new implementation is indeed faster). The test inputs are copied from those for log1p. Note that these changes make gen-auto-libm-tests depend on MPFR 4.2 (or later). The bulk of the changes are fairly generic for any such new function. (sysdeps/powerpc/nofpu/Makefile only needs changing for those type-generic templates that use fabs.) Tested for x86_64 and x86, and with build-many-glibcs.py.
44 lines
1.4 KiB
C
44 lines
1.4 KiB
C
/* Return base-2 logarithm of 1 + X.
|
|
Copyright (C) 2024 Free Software Foundation, Inc.
|
|
This file is part of the GNU C Library.
|
|
|
|
The GNU C Library is free software; you can redistribute it and/or
|
|
modify it under the terms of the GNU Lesser General Public
|
|
License as published by the Free Software Foundation; either
|
|
version 2.1 of the License, or (at your option) any later version.
|
|
|
|
The GNU C Library is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
Lesser General Public License for more details.
|
|
|
|
You should have received a copy of the GNU Lesser General Public
|
|
License along with the GNU C Library; if not, see
|
|
<https://www.gnu.org/licenses/>. */
|
|
|
|
#include <errno.h>
|
|
#include <math.h>
|
|
#include <math-underflow.h>
|
|
|
|
FLOAT
|
|
M_DECL_FUNC (__log2p1) (FLOAT x)
|
|
{
|
|
if (__glibc_unlikely (islessequal (x, M_LIT (-1.0))))
|
|
{
|
|
if (x == -1)
|
|
__set_errno (ERANGE);
|
|
else
|
|
__set_errno (EDOM);
|
|
}
|
|
if (isless (M_FABS (x), M_EPSILON / 4))
|
|
{
|
|
/* Avoid spurious underflows when log1p underflows but log2p1
|
|
should not. */
|
|
FLOAT ret = M_MLIT (M_LOG2E) * x;
|
|
math_check_force_underflow (ret);
|
|
return ret;
|
|
}
|
|
return M_MLIT (M_LOG2E) * M_SUF (__log1p) (x);
|
|
}
|
|
declare_mgen_alias (__log2p1, log2p1);
|