Backport of this upstream commit (with libm-test.inc adjustments):

commit c7de50250367167d8c9f35594b264f6a0af8dd0c

Author: Adhemerval Zanella <azanella@linux.vnet.ibm.com>

Date:   Fri Mar 14 12:49:45 2014 -0500

    PowerPC: remove wrong roundl implementation for PowerPC64

    The roundl assembly implementation

    (sysdeps/powerpc/powerpc64/fpu/s_roundl.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_roundl.c instead fixes the failing math.

    This fixes 16707.

Index: b/math/libm-test.inc

===================================================================

--- a/math/libm-test.inc

+++ b/math/libm-test.inc

@@ -9268,6 +9268,15 @@ round_test (void)

   TEST_f_f (round, -72057594037927936.75L, -72057594037927937.0L);

   TEST_f_f (round, -72057594037927937.5L, -72057594037927938.0L);

+  /* 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 (round,  34503599627370498.515625L, 34503599627370499.0L);

+  TEST_f_f (round, -34503599627370498.515625L, -34503599627370499.0L);

+# if LDBL_MANT_DIG >= 106

+  TEST_f_f (round,  1192568192774434123539907640624.484375L, 1192568192774434123539907640624.0L);

+  TEST_f_f (round, -1192568192774434123539907640624.484375L, -1192568192774434123539907640624.0L);

+# endif

+

   TEST_f_f (round, 10141204801825835211973625643007.5L, 10141204801825835211973625643008.0L);

   TEST_f_f (round, 10141204801825835211973625643008.25L, 10141204801825835211973625643008.0L);

   TEST_f_f (round, 10141204801825835211973625643008.5L, 10141204801825835211973625643009.0L);

Index: b/sysdeps/powerpc/powerpc64/fpu/s_roundl.S

===================================================================

--- a/sysdeps/powerpc/powerpc64/fpu/s_roundl.S

+++ /dev/null

@@ -1,132 +0,0 @@

-/* long double round function.

-   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

-.LC1:	/* 0.5 */

-	.tc FD_3fe00000_0[TC],0x3fe0000000000000

-	.section	".text"

-

-/* long double [fp1,fp2] roundl (long double x [fp1,fp2])

-   IEEE 1003.1 round function.  IEEE specifies "round to the nearest

-   integer value, rounding halfway cases away from zero, regardless of

-   the current rounding mode."  However PowerPC Architecture defines

-   "Round to Nearest" as "Choose the best approximation. In case of a

-   tie, choose the one that is even (least significant bit o).".

-   So we can't use the PowerPC "Round to Nearest" mode. Instead we set

-   "Round toward Zero" mode and round by adding +-0.5 before rounding

-   to the integer value.  */

-

-ENTRY (__roundl)

-	mffs	fp11		/* Save current FPU rounding mode.  */

-	lfd	fp13,.LC0@toc(2)

-	fabs	fp0,fp1

-	fabs	fp9,fp2

-	fsub	fp12,fp13,fp13	/* generate 0.0  */

-	fcmpu	cr7,fp0,fp13	/* if (fabs(x) > TWO52)  */

-	fcmpu	cr6,fp1,fp12	/* if (x > 0.0)  */

-	bnl-	cr7,.L2

-	mtfsfi	7,1		/* Set rounding mode toward 0.  */

-	lfd	fp10,.LC1@toc(2)

-	ble-	cr6,.L1

-	fneg	fp2,fp12

-	fadd	fp1,fp1,fp10	/* x+= 0.5;  */

-	fadd	fp1,fp1,fp13	/* x+= TWO52;  */

-	fsub	fp1,fp1,fp13	/* x-= TWO52;  */

-	fabs	fp1,fp1		/* if (x == 0.0) x = 0.0;  */

-.L0:

-	mtfsf	0x01,fp11	/* restore previous rounding mode.  */

-	blr

-.L1:

-	fsub	fp9,fp1,fp10	/* x-= 0.5;  */

-	fneg	fp2,fp12

-	bge-	cr6,.L0		/* if (x < 0.0)  */

-	fsub	fp1,fp9,fp13	/* x-= TWO52;  */

-	fadd	fp1,fp1,fp13	/* x+= TWO52;  */

-	fnabs	fp1,fp1		/* if (x == 0.0) x = -0.0;  */

-	mtfsf	0x01,fp11	/* restore previous rounding mode.  */

-	blr

-

-/* The high double is > TWO52 so we need to round the low double and

-   perhaps the high double.  In this case we have to round the low

-   double and handle any adjustment to the high double that may be

-   caused by rounding (up).  This is complicated by the fact that the

-   high double may already be rounded and the low double may have the

-   opposite sign to compensate.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 = rint(x1);

-   y_high = x0 + r1;

-   y_low = x0 - y_high + r1;

-   return y;  */

-.L2:

-	fcmpu	cr7,fp9,fp13	/* if (|x_low| > TWO52)  */

-	fcmpu	cr0,fp9,fp12	/* || (|x_low| == 0.0)  */

-	fcmpu	cr5,fp2,fp12	/* if (x_low > 0.0)  */

-	lfd	fp10,.LC1@toc(2)

-	bgelr-	cr7		/*   return x;	*/

-	beqlr-  cr0

-	mtfsfi	7,1		/* Set rounding mode toward 0.  */

-	fdiv	fp8,fp1,fp13	/* x_high/TWO52  */

-	

-	bng-	cr6,.L6		/* if (x > 0.0)  */

-	fctidz	fp0,fp8

-	fcfid	fp8,fp0		/* tau = floor(x_high/TWO52);  */

-	bng	cr5,.L4		/* if (x_low > 0.0)  */

-	fmr	fp3,fp1

-	fmr	fp4,fp2

-	b	.L5

-.L4:				/* if (x_low < 0.0)  */

-	fsub	fp3,fp1,fp8	/* x0 = x_high - tau;  */

-	fadd	fp4,fp2,fp8	/* x1 = x_low + tau;  */

-.L5:

-	fadd	fp5,fp4,fp10	/* r1 = x1 + 0.5;  */

-	fadd	fp5,fp5,fp13	/* r1 = r1 + TWO52;  */

-	fsub	fp5,fp5,fp13	/* r1 = r1 - TWO52;  */

-	b	.L9

-.L6:				/* if (x < 0.0)  */

-	fctidz	fp0,fp8

-	fcfid	fp8,fp0		/* tau = floor(x_high/TWO52);  */	

-	bnl	cr5,.L7		/* if (x_low < 0.0)  */

-	fmr	fp3,fp1

-	fmr	fp4,fp2

-	b	.L8

-.L7:				/* if (x_low > 0.0)  */

-	fsub	fp3,fp1,fp8	/* x0 = x_high - tau;  */

-	fadd	fp4,fp2,fp8	/* x1 = x_low + tau;  */

-.L8:

-	fsub	fp5,fp4,fp10	/* r1 = x1 - 0.5;  */

-	fsub	fp5,fp5,fp13	/* r1-= TWO52;  */

-	fadd	fp5,fp5,fp13	/* r1+= TWO52;  */

-.L9:

-	mtfsf	0x01,fp11	/* restore previous rounding mode.  */

-	fadd	fp1,fp3,fp5	/* y_high = x0 + r1;  */

-	fsub	fp2,fp3,fp1	/* y_low = x0 - y_high + r1;  */

-	fadd	fp2,fp2,fp5

-	blr

-END (__roundl)

-

-long_double_symbol (libm, __roundl, roundl)