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Fix powerpc64 lround, lroundf, llround, llroundf spurious "inexact" exceptions (bug 19235) [committed]

Message ID alpine.DEB.2.10.1511121624410.21729@digraph.polyomino.org.uk
State New
Headers show

Commit Message

Joseph Myers Nov. 12, 2015, 4:25 p.m. UTC 
Similar to bug 19134 for powerpc32, the powerpc64 implementations of
lround, lroundf, llround, llroundf can raise spurious "inexact"
exceptions for integer arguments from adding 0.5 then converting to
integer (this does not apply to the power5+ version for double, which
uses the frin instruction which is defined never to raise "inexact"; I
don't know why power5+ doesn't use that version for float as well).

This patch fixes the bug in a similar way to the powerpc32 bug, by
testing for integers (adding and subtracting 2^52 and comparing with
the value before that addition and subtraction) and not adding 0.5 in
that case.

The powerpc maintainers may wish to look at making power5+ / power6x /
power8 use frin for float lround / llround as well as for double,
unless there's some reason I've missed that this isn't beneficial.

Tested for powerpc64.  Committed.

2015-11-12  Joseph Myers  <joseph@codesourcery.com>

	[BZ #19235]
	* sysdeps/powerpc/powerpc64/fpu/s_llround.S (__llround): Do not
	add 0.5 to integer arguments.
	* sysdeps/powerpc/powerpc64/fpu/s_llroundf.S (__llroundf):
	Likewise.
	(.LC2): New object.
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Patch

diff --git a/sysdeps/powerpc/powerpc64/fpu/s_llround.S b/sysdeps/powerpc/powerpc64/fpu/s_llround.S
index 321925e..bc433bc 100644
--- a/sysdeps/powerpc/powerpc64/fpu/s_llround.S
+++ b/sysdeps/powerpc/powerpc64/fpu/s_llround.S
@@ -55,6 +55,11 @@  ENTRY (__llround)
 	fcmpu	cr1,fp1,fp12	/* x is negative? x < 0.0  */
 	blt-	cr6,.Lretzero	/* 0.5 > x < -0.5 so just return 0.  */
 	bge-	cr7,.Lnobias	/* 2^52 > x < -2^52 just convert with no bias.  */
+	/* Test whether an integer to avoid spurious "inexact".  */
+	fadd	fp3,fp2,fp9
+	fsub	fp3,fp3,fp9
+	fcmpu	cr5,fp2,fp3
+	beq	cr5,.Lnobias
 	fadd	fp3,fp2,fp10	/* |x|+=0.5 bias to prepare to round.  */
 	bge	cr1,.Lconvert	/* x is positive so don't negate x.  */
 	fnabs	fp3,fp3		/* -(|x|+=0.5)  */
diff --git a/sysdeps/powerpc/powerpc64/fpu/s_llroundf.S b/sysdeps/powerpc/powerpc64/fpu/s_llroundf.S
index fc5aa77..e8a8bf8 100644
--- a/sysdeps/powerpc/powerpc64/fpu/s_llroundf.S
+++ b/sysdeps/powerpc/powerpc64/fpu/s_llroundf.S
@@ -23,6 +23,8 @@ 
 	.tc FD_41600000_0[TC],0x4160000000000000
 .LC1:	/* 0.5 */
 	.tc FD_3fe00000_0[TC],0x3fe0000000000000
+.LC2:	/* 2^52 */
+	.tc FD_43300000_0[TC],0x4330000000000000
 	.section	".text"
 
 /* long long [r3] llroundf (float x [fp1])
@@ -47,6 +49,7 @@  ENTRY (__llroundf)
 	CALL_MCOUNT 0
 	lfd	fp9,.LC0@toc(2)	/* Load 2^23 into fpr9.  */
 	lfd	fp10,.LC1@toc(2)/* Load 0.5 into fpr10.  */
+	lfd	fp11,.LC2@toc(2)	/* Load 2^52 into fpr11.  */
 	fabs	fp2,fp1		/* Get the absolute value of x.  */
 	fsub	fp12,fp10,fp10	/* Compute 0.0 into fp12.  */
 	fcmpu	cr6,fp2,fp10	/* if |x| < 0.5  */
@@ -54,6 +57,11 @@  ENTRY (__llroundf)
 	fcmpu	cr1,fp1,fp12	/* x is negative? x < 0.0  */
 	blt-	cr6,.Lretzero	/* 0.5 > x < -0.5 so just return 0.  */
 	bge-	cr7,.Lnobias	/* 2^23 > x < -2^23 just convert with no bias.  */
+	/* Test whether an integer to avoid spurious "inexact".  */
+	fadd	fp3,fp2,fp11
+	fsub	fp3,fp3,fp11
+	fcmpu	cr5,fp2,fp3
+	beq	cr5,.Lnobias
 	fadd	fp3,fp2,fp10	/* |x|+=0.5 bias to prepare to round.  */
 	bge	cr1,.Lconvert	/* x is positive so don't negate x.  */
 	fnabs	fp3,fp3		/* -(|x|+=0.5)  */