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Backport of this upstream commit (with libm-test.inc adjustments):
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commit 98fb27a373f37554232e0060eef1a5bb00a07eb0
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Author: Adhemerval Zanella <azanella@linux.vnet.ibm.com>
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Date: Fri Mar 14 12:27:52 2014 -0500
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PowerPC: remove wrong nearbyintl implementation for PPC64
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The nearbyintl assembly implementation
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(sysdeps/powerpc/powerpc64/fpu/s_nearbyintl.S)
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returns wrong results for some inputs where first double is a exact
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integer and the precision is determined by second long double.
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Checking on implementation comments and history, I am very confident the
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assembly implementation was based on a version before commit
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5c68d401698a58cf7da150d9cce769fa6679ba5f that fixes BZ#2423 (Errors in
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long double (ldbl-128ibm) rounding functions in glibc-2.4).
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By just removing the implementation and make the build select
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sysdeps/ieee754/ldbl-128ibm/s_nearbyintl.c instead fixes the failing
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math.
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Fixes BZ#16706.
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Index: b/math/libm-test.inc
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===================================================================
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--- a/math/libm-test.inc
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+++ b/math/libm-test.inc
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@@ -7619,6 +7619,16 @@ nearbyint_test (void)
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TEST_f_f (nearbyint, -562949953421312.75, -562949953421313.0);
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TEST_f_f (nearbyint, -1125899906842624.75, -1125899906842625.0);
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#endif
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+#ifdef TEST_LDOUBLE
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+ /* Check cases where first double is a exact integer higher than 2^52 and
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+ the precision is determined by second long double for IBM long double. */
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+ TEST_f_f (nearbyint, 34503599627370498.515625L, 34503599627370499.0L);
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+ TEST_f_f (nearbyint, -34503599627370498.515625L, -34503599627370499.0L);
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+# if LDBL_MANT_DIG >= 106
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+ TEST_f_f (nearbyint, 1192568192774434123539907640624.484375L, 1192568192774434123539907640624.0L);
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+ TEST_f_f (nearbyint, -1192568192774434123539907640624.484375L, -1192568192774434123539907640624.0L);
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+# endif
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+#endif
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END (nearbyint);
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}
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Index: b/sysdeps/powerpc/powerpc64/fpu/s_nearbyintl.S
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===================================================================
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--- a/sysdeps/powerpc/powerpc64/fpu/s_nearbyintl.S
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+++ /dev/null
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@@ -1,113 +0,0 @@
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-/* nearbyint long double.
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- IBM extended format long double version.
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- Copyright (C) 2004, 2006 Free Software Foundation, Inc.
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- This file is part of the GNU C Library.
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-
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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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-
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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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-
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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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- <http://www.gnu.org/licenses/>. */
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-
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-#include <sysdep.h>
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-#include <math_ldbl_opt.h>
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-
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- .section ".toc","aw"
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-.LC0: /* 2**52 */
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- .tc FD_43300000_0[TC],0x4330000000000000
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- .section ".text"
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-
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-/* long double [fp1,fp2] nearbyintl (long double x [fp1,fp2])
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- IEEE 1003.1 nearbyintl function. nearbyintl is simular to the rintl
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- but does raise the "inexact" exception. This implementation is
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- based on rintl but explicitly maskes the inexact exception on entry
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- and clears any pending inexact before restoring the exception mask
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- on exit.
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-
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- PowerPC64 long double uses the IBM extended format which is
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- represented two 64-floating point double values. The values are
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- non-overlapping giving an effective precision of 106 bits. The first
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- double contains the high order bits of mantisa and is always rounded
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- to represent a normal rounding of long double to double. Since the
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- long double value is sum of the high and low values, the low double
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- normally has the opposite sign to compensate for the this rounding.
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-
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- For long double there are two cases:
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- 1) |x| < 2**52, all the integer bits are in the high double.
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- floor the high double and set the low double to -0.0.
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- 2) |x| >= 2**52, Rounding involves both doubles.
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- See the comment before lable .L2 for details.
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- */
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-ENTRY (__nearbyintl)
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- mffs fp11 /* Save current FPSCR. */
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- lfd fp13,.LC0@toc(2)
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- fabs fp0,fp1
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- mtfsb0 28 /* Disable "inexact" exceptions. */
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- fsub fp12,fp13,fp13 /* generate 0.0 */
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- fabs fp9,fp2
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- fcmpu cr7,fp0,fp13 /* if (fabs(x) > TWO52) */
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- fcmpu cr6,fp1,fp12 /* if (x > 0.0) */
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- bnl- cr7,.L2
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- fmr fp2,fp12
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- bng- cr6,.L4
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- fadd fp1,fp1,fp13 /* x+= TWO52; */
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- fsub fp1,fp1,fp13 /* x-= TWO52; */
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- b .L9
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-.L4:
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- bnl- cr6,.L9 /* if (x < 0.0) */
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- fsub fp1,fp13,fp1 /* x = TWO52 - x; */
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- fsub fp0,fp1,fp13 /* x = - (x - TWO52); */
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- fneg fp1,fp0
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-.L9:
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- mtfsb0 6 /* Clear any pending "inexact" exceptions. */
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- mtfsf 0x01,fp11 /* restore exception mask. */
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- blr
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-
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-/* The high double is > TWO52 so we need to round the low double and
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- perhaps the high double. This gets a bit tricky so we use the
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- following algorithm:
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-
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- tau = floor(x_high/TWO52);
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- x0 = x_high - tau;
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- x1 = x_low + tau;
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- r1 = nearbyint(x1);
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- y_high = x0 + r1;
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- y_low = r1 - tau;
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- return y; */
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-.L2:
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- fcmpu cr7,fp9,fp13 /* if (|x_low| > TWO52) */
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- fcmpu cr0,fp9,fp12 /* || (|x_low| == 0.0) */
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- bge- cr7,.L9 /* return x; */
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- beq- cr0,.L9
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- fdiv fp8,fp1,fp13 /* x_high/TWO52 */
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- fctidz fp0,fp8
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- fcfid fp8,fp0 /* tau = floor(x_high/TWO52); */
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- fsub fp3,fp1,fp8 /* x0 = x_high - tau; */
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- fadd fp4,fp2,fp8 /* x1 = x_low + tau; */
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-
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- fcmpu cr6,fp4,fp12 /* if (x1 > 0.0) */
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- bng- cr6,.L8
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- fadd fp5,fp4,fp13 /* r1 = x1 + TWO52; */
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- fsub fp5,fp5,fp13 /* r1 = r1 - TWO52; */
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- b .L6
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-.L8:
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- fmr fp5,fp4
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- bge- cr6,.L6 /* if (x1 < 0.0) */
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- fsub fp5,fp13,fp4 /* r1 = TWO52 - x1; */
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- fsub fp0,fp5,fp13 /* r1 = - (r1 - TWO52); */
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- fneg fp5,fp0
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-.L6:
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- fadd fp1,fp3,fp5 /* y_high = x0 + r1; */
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- fsub fp2,fp5,fp8 /* y_low = r1 - tau; */
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- b .L9
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-END (__nearbyintl)
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-
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-long_double_symbol (libm, __nearbyintl, nearbyintl)
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