[3/3] PowerPC: remove wrong roundl implementation for PowerPC64
diff mbox

Message ID 53230A15.9060203@linux.vnet.ibm.com
State New
Headers show

Commit Message

Adhemerval Zanella March 14, 2014, 1:54 p.m. UTC
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.

Fixes BZ#16707.

Test on PPC64 and PPC64LE. If no one opposes it, I'll commit in a couple
of hours.

--

2014-03-14  Adhemerval Zanella  <azanella@linux.vnet.ibm.com>

	[BZ #16707]
	* sysdeps/powerpc/powerpc64/fpu/s_roundl.S: Remove wrong
	implementation.
	* math/libm-test.inc (round_test_data): Add more tests.

---

Comments

Adhemerval Zanella March 14, 2014, 6:05 p.m. UTC | #1
On 14-03-2014 10:54, Adhemerval Zanella wrote:
> 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.
>
> Fixes BZ#16707.
>
> Test on PPC64 and PPC64LE. If no one opposes it, I'll commit in a couple
> of hours.
>

Pushed as 98fb27a373f37554232e0060eef1a5bb00a07eb0 with the LDBL_MANT_DIG guards.
Adhemerval Zanella March 14, 2014, 6:06 p.m. UTC | #2
On 14-03-2014 10:54, Adhemerval Zanella wrote:
> 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.
>
> Fixes BZ#16707.
>
> Test on PPC64 and PPC64LE. If no one opposes it, I'll commit in a couple
> of hours.


Pushed as c7de50250367167d8c9f35594b264f6a0af8dd0c with the LDBL_MANT_DIG guards.

Patch
diff mbox

diff --git a/NEWS b/NEWS
index c9bfcb8..443b146 100644
--- a/NEWS
+++ b/NEWS
@@ -11,7 +11,7 @@  Version 2.20
 
   15347, 15804, 15894, 16447, 16532, 16545, 16574, 16600, 16609, 16610,
   16611, 16613, 16623, 16632, 16639, 16642, 16670, 16674, 16677, 16683,
-  16689, 16695, 16701, 16706.
+  16689, 16695, 16701, 16706, 16707.
 
 * The am33 port, which had not worked for several years, has been removed
   from ports.
diff --git a/math/libm-test.inc b/math/libm-test.inc
index ee0a353..378c79d 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -10625,6 +10625,13 @@  static const struct test_f_f_data round_test_data[] =
     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,  1192568192774434123539907640624.484375L, 1192568192774434123539907640624.0L),
+    TEST_f_f (round, -34503599627370498.515625L, -34503599627370499.0L),
+    TEST_f_f (round, -1192568192774434123539907640624.484375L, -1192568192774434123539907640624.0L),
+
     TEST_f_f (round, 10141204801825835211973625643007.5L, 10141204801825835211973625643008.0L),
     TEST_f_f (round, 10141204801825835211973625643008.25L, 10141204801825835211973625643008.0L),
     TEST_f_f (round, 10141204801825835211973625643008.5L, 10141204801825835211973625643009.0L),
diff --git a/sysdeps/powerpc/powerpc64/fpu/s_roundl.S b/sysdeps/powerpc/powerpc64/fpu/s_roundl.S
deleted file mode 100644
index 5362da8..0000000
--- 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) 2004-2014 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)