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Backport of this upstream commit (with libm-test.inc adjustments):
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commit c7de50250367167d8c9f35594b264f6a0af8dd0c
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Author: Adhemerval Zanella <azanella@linux.vnet.ibm.com>
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Date:   Fri Mar 14 12:49:45 2014 -0500
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    PowerPC: remove wrong roundl implementation for PowerPC64
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    The roundl assembly implementation
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    (sysdeps/powerpc/powerpc64/fpu/s_roundl.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_roundl.c instead fixes the failing math.
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    This fixes 16707.
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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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@@ -9268,6 +9268,15 @@ round_test (void)
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   TEST_f_f (round, -72057594037927936.75L, -72057594037927937.0L);
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   TEST_f_f (round, -72057594037927937.5L, -72057594037927938.0L);
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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 (round,  34503599627370498.515625L, 34503599627370499.0L);
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+  TEST_f_f (round, -34503599627370498.515625L, -34503599627370499.0L);
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+# if LDBL_MANT_DIG >= 106
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+  TEST_f_f (round,  1192568192774434123539907640624.484375L, 1192568192774434123539907640624.0L);
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+  TEST_f_f (round, -1192568192774434123539907640624.484375L, -1192568192774434123539907640624.0L);
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+# endif
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+
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   TEST_f_f (round, 10141204801825835211973625643007.5L, 10141204801825835211973625643008.0L);
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   TEST_f_f (round, 10141204801825835211973625643008.25L, 10141204801825835211973625643008.0L);
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   TEST_f_f (round, 10141204801825835211973625643008.5L, 10141204801825835211973625643009.0L);
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Index: b/sysdeps/powerpc/powerpc64/fpu/s_roundl.S
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===================================================================
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--- a/sysdeps/powerpc/powerpc64/fpu/s_roundl.S
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+++ /dev/null
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@@ -1,132 +0,0 @@
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-/* long double round function.
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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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-.LC1:	/* 0.5 */
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-	.tc FD_3fe00000_0[TC],0x3fe0000000000000
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-	.section	".text"
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-
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-/* long double [fp1,fp2] roundl (long double x [fp1,fp2])
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-   IEEE 1003.1 round 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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-
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-ENTRY (__roundl)
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-	mffs	fp11		/* Save current FPU rounding mode.  */
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-	lfd	fp13,.LC0@toc(2)
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-	fabs	fp0,fp1
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-	fabs	fp9,fp2
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-	fsub	fp12,fp13,fp13	/* generate 0.0  */
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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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-	mtfsfi	7,1		/* Set rounding mode toward 0.  */
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-	lfd	fp10,.LC1@toc(2)
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-	ble-	cr6,.L1
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-	fneg	fp2,fp12
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-	fadd	fp1,fp1,fp10	/* x+= 0.5;  */
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-	fadd	fp1,fp1,fp13	/* x+= TWO52;  */
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-	fsub	fp1,fp1,fp13	/* x-= TWO52;  */
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-	fabs	fp1,fp1		/* if (x == 0.0) x = 0.0;  */
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-.L0:
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-	mtfsf	0x01,fp11	/* restore previous rounding mode.  */
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-	blr
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-.L1:
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-	fsub	fp9,fp1,fp10	/* x-= 0.5;  */
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-	fneg	fp2,fp12
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-	bge-	cr6,.L0		/* if (x < 0.0)  */
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-	fsub	fp1,fp9,fp13	/* x-= TWO52;  */
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-	fadd	fp1,fp1,fp13	/* x+= TWO52;  */
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-	fnabs	fp1,fp1		/* if (x == 0.0) x = -0.0;  */
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-	mtfsf	0x01,fp11	/* restore previous rounding mode.  */
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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.  In this case we have to round the low
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-   double and handle any adjustment to the high double that may be
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-   caused by rounding (up).  This is complicated by the fact that the
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-   high double may already be rounded and the low double may have the
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-   opposite sign to compensate.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 = rint(x1);
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-   y_high = x0 + r1;
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-   y_low = x0 - y_high + r1;
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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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-	fcmpu	cr5,fp2,fp12	/* if (x_low > 0.0)  */
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-	lfd	fp10,.LC1@toc(2)
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-	bgelr-	cr7		/*   return x;	*/
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-	beqlr-  cr0
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-	mtfsfi	7,1		/* Set rounding mode toward 0.  */
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-	fdiv	fp8,fp1,fp13	/* x_high/TWO52  */
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-	
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-	bng-	cr6,.L6		/* if (x > 0.0)  */
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-	fctidz	fp0,fp8
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-	fcfid	fp8,fp0		/* tau = floor(x_high/TWO52);  */
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-	bng	cr5,.L4		/* if (x_low > 0.0)  */
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-	fmr	fp3,fp1
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-	fmr	fp4,fp2
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-	b	.L5
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-.L4:				/* if (x_low < 0.0)  */
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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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-.L5:
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-	fadd	fp5,fp4,fp10	/* r1 = x1 + 0.5;  */
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-	fadd	fp5,fp5,fp13	/* r1 = r1 + TWO52;  */
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-	fsub	fp5,fp5,fp13	/* r1 = r1 - TWO52;  */
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-	b	.L9
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-.L6:				/* if (x < 0.0)  */
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-	fctidz	fp0,fp8
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-	fcfid	fp8,fp0		/* tau = floor(x_high/TWO52);  */	
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-	bnl	cr5,.L7		/* if (x_low < 0.0)  */
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-	fmr	fp3,fp1
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-	fmr	fp4,fp2
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-	b	.L8
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-.L7:				/* if (x_low > 0.0)  */
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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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-.L8:
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-	fsub	fp5,fp4,fp10	/* r1 = x1 - 0.5;  */
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-	fsub	fp5,fp5,fp13	/* r1-= TWO52;  */
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-	fadd	fp5,fp5,fp13	/* r1+= TWO52;  */
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-.L9:
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-	mtfsf	0x01,fp11	/* restore previous rounding mode.  */
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-	fadd	fp1,fp3,fp5	/* y_high = x0 + r1;  */
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-	fsub	fp2,fp3,fp1	/* y_low = x0 - y_high + r1;  */
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-	fadd	fp2,fp2,fp5
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-	blr
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-END (__roundl)
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-
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-long_double_symbol (libm, __roundl, roundl)