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44 lines
1.4 KiB
C
44 lines
1.4 KiB
C
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/* Return base-2 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-underflow.h>
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FLOAT
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M_DECL_FUNC (__log2p1) (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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/* Avoid spurious underflows when log1p underflows but log2p1
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should not. */
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FLOAT ret = M_MLIT (M_LOG2E) * x;
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math_check_force_underflow (ret);
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return ret;
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}
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return M_MLIT (M_LOG2E) * M_SUF (__log1p) (x);
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}
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declare_mgen_alias (__log2p1, log2p1);
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