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Re: [PATCH] PowerPC: remove wrong truncl implementation for PowerPC64


I forgot to add that I'll create a bugzilla for the truncl on PPC64 and
send a patch to add some test inputs for 2.20.


On 07-01-2014 20:05, Adhemerval Zanella wrote:
> While seeking why some tgammal results shows wrong signal on PPC64, I found
> out that the assembly implementation truncl (sysdeps/powerpc/powerpc64/fpu/s_truncl.S)
> for is in fact returning wrong results for some inputs. More specifically,
> for number where the 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), since
> the implementation indeed does not handle some inputs correctly.
>
> By just removing the implementation and make the build select 
> sysdeps/ieee754/ldbl-128ibm/s_truncl.c instead it fixes the tgammal
> issues.
>
> Tested on PPC64.
>
> ---
>
> 2014-01-07  Adhemerval Zanella  <azanella@linux.vnet.ibm.com>
>
> 	* sysdeps/powerpc/powerpc64/fpu/s_truncl.S: Remove wrong
> 	implementation.
> 	* sysdeps/ieee754/ldbl-128ibm/s_truncl.c: Remove bogus comment.
>
> --
>
> diff --git a/sysdeps/ieee754/ldbl-128ibm/s_truncl.c b/sysdeps/ieee754/ldbl-128ibm/s_truncl.c
> index 490ad26..aca3f3e 100644
> --- a/sysdeps/ieee754/ldbl-128ibm/s_truncl.c
> +++ b/sysdeps/ieee754/ldbl-128ibm/s_truncl.c
> @@ -17,9 +17,6 @@
>     License along with the GNU C Library; if not, see
>     <http://www.gnu.org/licenses/>.  */
>
> -/* This has been coded in assembler because GCC makes such a mess of it
> -   when it's coded in C.  */
> -
>  #include <math.h>
>  #include <math_ldbl_opt.h>
>  #include <float.h>
> diff --git a/sysdeps/powerpc/powerpc64/fpu/s_truncl.S b/sysdeps/powerpc/powerpc64/fpu/s_truncl.S
> deleted file mode 100644
> index e5a3008..0000000
> --- a/sysdeps/powerpc/powerpc64/fpu/s_truncl.S
> +++ /dev/null
> @@ -1,120 +0,0 @@
> -/* long double trunc 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] truncl (long double x [fp1,fp2])  */
> -
> -ENTRY (__truncl)
> -	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.  */
> -	ble-	cr6,.L1
> -	fneg	fp2,fp12
> -	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:
> -	fneg	fp2,fp12
> -	bge-	cr6,.L0		/* if (x < 0.0)  */
> -	fsub	fp1,fp1,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)  */
> -	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);  */
> -	fadd	fp8,fp8,fp8	/* tau++; Make tau even  */
> -	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,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);  */
> -	fadd	fp8,fp8,fp8	/* tau++; Make tau even  */
> -	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,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 (__truncl)
> -
> -long_double_symbol (libm, __truncl, truncl)
>


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