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84 lines
2.7 KiB
C
84 lines
2.7 KiB
C
/* Round to nearest integer. PowerPC64 version.
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Copyright (C) 2019-2024 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 Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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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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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If
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not, see <https://www.gnu.org/licenses/>. */
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#define NO_MATH_REDIRECT
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#define lround __redirect_lround
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#define __lround __redirect___lround
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#include <math.h>
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#undef lround
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#undef __lround
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#include <libm-alias-double.h>
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#include <math-barriers.h>
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long long int
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__llround (double x)
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{
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#ifdef _ARCH_PWR5X
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double r = __builtin_round (x);
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/* Prevent gcc from calling llround directly when compiled with
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-fno-math-errno by inserting a barrier. */
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math_opt_barrier (r);
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return r;
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#else
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/* IEEE 1003.1 llround function. IEEE specifies "round to the nearest
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integer value, rounding halfway cases away from zero, regardless of
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the current rounding mode." However PowerPC Architecture defines
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"round to Nearest" as "Choose the best approximation. In case of a
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tie, choose the one that is even (least significant bit o).".
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So we can't use the PowerPC "round to Nearest" mode. Instead we set
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"round toward Zero" mode and round by adding +-0.5 before rounding
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to the integer value.
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It is necessary to detect when x is (+-)0x1.fffffffffffffp-2
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because adding +-0.5 in this case will cause an erroneous shift,
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carry and round. We simply return 0 if 0.5 > x > -0.5. Likewise
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if x is and odd number between +-(2^52 and 2^53-1) a shift and
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carry will erroneously round if biased with +-0.5. Therefore if x
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is greater/less than +-2^52 we don't need to bias the number with
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+-0.5. */
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double ax = fabs (x);
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if (ax < 0.5)
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return 0;
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if (ax < 0x1p+52)
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{
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/* Test whether an integer to avoid spurious "inexact". */
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double t = ax + 0x1p+52;
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t = t - 0x1p+52;
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if (ax != t)
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{
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ax = ax + 0.5;
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if (x < 0.0)
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ax = -fabs (ax);
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x = ax;
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}
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}
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long int ret;
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__asm__ ("fctidz %0, %1" : "=d" (ret) : "d" (x));
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return ret;
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#endif
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}
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#ifndef __llround
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strong_alias (__llround, __lround)
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libm_alias_double (__llround, llround)
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libm_alias_double (__lround, lround)
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#endif
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