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55eb99e9a9
C23 adds various <math.h> function families originally defined in TS 18661-4. Add the log10p1 functions (log10(1+x): like log1p, but for base-10 logarithms). This is directly analogous to the log2p1 implementation (except that whereas log2p1 has a smaller underflow range than log1p, log10p1 has a larger underflow range). The test inputs are copied from those for log1p and log2p1, plus a few more inputs in that wider underflow range. Tested for x86_64 and x86, and with build-many-glibcs.py.
50 lines
1.7 KiB
C
50 lines
1.7 KiB
C
/* Return base-10 logarithm of 1 + X.
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Copyright (C) 2024 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <errno.h>
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#include <math.h>
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#include <math-narrow-eval.h>
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#include <math-underflow.h>
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FLOAT
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M_DECL_FUNC (__log10p1) (FLOAT x)
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{
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if (__glibc_unlikely (islessequal (x, M_LIT (-1.0))))
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{
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if (x == -1)
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__set_errno (ERANGE);
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else
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__set_errno (EDOM);
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}
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if (isless (M_FABS (x), M_EPSILON / 4))
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{
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/* Ensure appropriate underflows (a wider range than for log1p,
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with potential for zero results from nonzero arguments, in
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which case errno should be set based on the result with any
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excess range and precision removed) even if the result of
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multiplying by M_MLIT (M_LOG10E) is exact. */
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FLOAT ret = math_narrow_eval (M_MLIT (M_LOG10E) * x);
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math_check_force_underflow (ret);
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if (x != 0 && ret == 0)
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__set_errno (ERANGE);
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return ret;
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}
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return M_MLIT (M_LOG10E) * M_SUF (__log1p) (x);
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}
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declare_mgen_alias (__log10p1, log10p1);
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