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66 lines
1.9 KiB
C
66 lines
1.9 KiB
C
/* Return exp2(X) - 1.
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Copyright (C) 2024-2025 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 <fenv.h>
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#include <math.h>
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#include <math_private.h>
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#include <math-underflow.h>
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FLOAT
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M_DECL_FUNC (__exp2m1) (FLOAT x)
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{
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if (isgreaterequal (x, M_LIT (-1.0)) && islessequal (x, M_LIT (1.0)))
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{
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FLOAT ret = M_SUF (__expm1) (M_MLIT (M_LN2) * 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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else if (isgreater (x, M_MANT_DIG + M_LIT (2.0)))
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{
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#if defined FE_DOWNWARD || defined FE_TOWARDZERO
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/* exp2m1 (MAX_EXP) should not overflow in these two rounding
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modes, but exp2 does overflow. */
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if (x == M_MAX_EXP)
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{
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int rnd_mode = fegetround ();
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if (0
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# ifdef FE_DOWNWARD
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|| rnd_mode == FE_DOWNWARD
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# endif
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# ifdef FE_TOWARDZERO
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|| rnd_mode == FE_TOWARDZERO
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# endif
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)
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return M_MAX;
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}
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#endif
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FLOAT ret = M_SUF (__ieee754_exp2) (x);
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if (!isfinite (ret) && isfinite (x))
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__set_errno (ERANGE);
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return ret;
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}
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else if (isless (x, -M_MANT_DIG - M_LIT (2.0)))
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return M_LIT (-1.0);
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else
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return M_SUF (__ieee754_exp2) (x) - M_LIT (1.0);
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}
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declare_mgen_alias (__exp2m1, exp2m1);
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