Backport of this upstream commit (with libm-test.inc adjustments):
commit 98fb27a373f37554232e0060eef1a5bb00a07eb0
Author: Adhemerval Zanella <azanella@linux.vnet.ibm.com>
Date: Fri Mar 14 12:27:52 2014 -0500
PowerPC: remove wrong nearbyintl implementation for PPC64
The nearbyintl assembly implementation
(sysdeps/powerpc/powerpc64/fpu/s_nearbyintl.S)
returns wrong results for some inputs where first double is a exact
integer and the precision is determined by second long double.
Checking on implementation comments and history, I am very confident the
assembly implementation was based on a version before commit
5c68d401698a58cf7da150d9cce769fa6679ba5f that fixes BZ#2423 (Errors in
long double (ldbl-128ibm) rounding functions in glibc-2.4).
By just removing the implementation and make the build select
sysdeps/ieee754/ldbl-128ibm/s_nearbyintl.c instead fixes the failing
math.
Fixes BZ#16706.
Index: b/math/libm-test.inc
===================================================================
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -7619,6 +7619,16 @@ nearbyint_test (void)
TEST_f_f (nearbyint, -562949953421312.75, -562949953421313.0);
TEST_f_f (nearbyint, -1125899906842624.75, -1125899906842625.0);
#endif
+#ifdef TEST_LDOUBLE
+ /* Check cases where first double is a exact integer higher than 2^52 and
+ the precision is determined by second long double for IBM long double. */
+ TEST_f_f (nearbyint, 34503599627370498.515625L, 34503599627370499.0L);
+ TEST_f_f (nearbyint, -34503599627370498.515625L, -34503599627370499.0L);
+# if LDBL_MANT_DIG >= 106
+ TEST_f_f (nearbyint, 1192568192774434123539907640624.484375L, 1192568192774434123539907640624.0L);
+ TEST_f_f (nearbyint, -1192568192774434123539907640624.484375L, -1192568192774434123539907640624.0L);
+# endif
+#endif
END (nearbyint);
}
Index: b/sysdeps/powerpc/powerpc64/fpu/s_nearbyintl.S
===================================================================
--- a/sysdeps/powerpc/powerpc64/fpu/s_nearbyintl.S
+++ /dev/null
@@ -1,113 +0,0 @@
-/* nearbyint long double.
- IBM extended format long double version.
- Copyright (C) 2004, 2006 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
-
- The GNU C Library is free software; you can redistribute it and/or
- modify it under the terms of the GNU Lesser General Public
- License as published by the Free Software Foundation; either
- version 2.1 of the License, or (at your option) any later version.
-
- The GNU C Library is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public
- License along with the GNU C Library; if not, see
- <http://www.gnu.org/licenses/>. */
-
-#include <sysdep.h>
-#include <math_ldbl_opt.h>
-
- .section ".toc","aw"
-.LC0: /* 2**52 */
- .tc FD_43300000_0[TC],0x4330000000000000
- .section ".text"
-
-/* long double [fp1,fp2] nearbyintl (long double x [fp1,fp2])
- IEEE 1003.1 nearbyintl function. nearbyintl is simular to the rintl
- but does raise the "inexact" exception. This implementation is
- based on rintl but explicitly maskes the inexact exception on entry
- and clears any pending inexact before restoring the exception mask
- on exit.
-
- PowerPC64 long double uses the IBM extended format which is
- represented two 64-floating point double values. The values are
- non-overlapping giving an effective precision of 106 bits. The first
- double contains the high order bits of mantisa and is always rounded
- to represent a normal rounding of long double to double. Since the
- long double value is sum of the high and low values, the low double
- normally has the opposite sign to compensate for the this rounding.
-
- For long double there are two cases:
- 1) |x| < 2**52, all the integer bits are in the high double.
- floor the high double and set the low double to -0.0.
- 2) |x| >= 2**52, Rounding involves both doubles.
- See the comment before lable .L2 for details.
- */
-ENTRY (__nearbyintl)
- mffs fp11 /* Save current FPSCR. */
- lfd fp13,.LC0@toc(2)
- fabs fp0,fp1
- mtfsb0 28 /* Disable "inexact" exceptions. */
- fsub fp12,fp13,fp13 /* generate 0.0 */
- fabs fp9,fp2
- fcmpu cr7,fp0,fp13 /* if (fabs(x) > TWO52) */
- fcmpu cr6,fp1,fp12 /* if (x > 0.0) */
- bnl- cr7,.L2
- fmr fp2,fp12
- bng- cr6,.L4
- fadd fp1,fp1,fp13 /* x+= TWO52; */
- fsub fp1,fp1,fp13 /* x-= TWO52; */
- b .L9
-.L4:
- bnl- cr6,.L9 /* if (x < 0.0) */
- fsub fp1,fp13,fp1 /* x = TWO52 - x; */
- fsub fp0,fp1,fp13 /* x = - (x - TWO52); */
- fneg fp1,fp0
-.L9:
- mtfsb0 6 /* Clear any pending "inexact" exceptions. */
- mtfsf 0x01,fp11 /* restore exception mask. */
- blr
-
-/* The high double is > TWO52 so we need to round the low double and
- perhaps the high double. This gets a bit tricky so we use the
- following algorithm:
-
- tau = floor(x_high/TWO52);
- x0 = x_high - tau;
- x1 = x_low + tau;
- r1 = nearbyint(x1);
- y_high = x0 + r1;
- y_low = r1 - tau;
- return y; */
-.L2:
- fcmpu cr7,fp9,fp13 /* if (|x_low| > TWO52) */
- fcmpu cr0,fp9,fp12 /* || (|x_low| == 0.0) */
- bge- cr7,.L9 /* return x; */
- beq- cr0,.L9
- fdiv fp8,fp1,fp13 /* x_high/TWO52 */
- fctidz fp0,fp8
- fcfid fp8,fp0 /* tau = floor(x_high/TWO52); */
- fsub fp3,fp1,fp8 /* x0 = x_high - tau; */
- fadd fp4,fp2,fp8 /* x1 = x_low + tau; */
-
- fcmpu cr6,fp4,fp12 /* if (x1 > 0.0) */
- bng- cr6,.L8
- fadd fp5,fp4,fp13 /* r1 = x1 + TWO52; */
- fsub fp5,fp5,fp13 /* r1 = r1 - TWO52; */
- b .L6
-.L8:
- fmr fp5,fp4
- bge- cr6,.L6 /* if (x1 < 0.0) */
- fsub fp5,fp13,fp4 /* r1 = TWO52 - x1; */
- fsub fp0,fp5,fp13 /* r1 = - (r1 - TWO52); */
- fneg fp5,fp0
-.L6:
- fadd fp1,fp3,fp5 /* y_high = x0 + r1; */
- fsub fp2,fp5,fp8 /* y_low = r1 - tau; */
- b .L9
-END (__nearbyintl)
-
-long_double_symbol (libm, __nearbyintl, nearbyintl)