[BZ4997]

	* sysdeps/powerpc/powerpc32/fpu/s_lround.S (__lround): Fixed erroneous
	result when x is +/-nextafter(+/-0.5,-/+1) i.e. all 1's in the
	mantissa.
	* sysdeps/powerpc/powerpc32/power4/fpu/s_llround.S (__llround):
	Likewise.  Also account for when x is an odd number between 2^52
	and 2^53-1.
	* sysdeps/powerpc/powerpc64/fpu/s_llround.S (__llround): Likewise.
	* sysdeps/powerpc/powerpc64/fpu/s_llroundf.S (__llroundf): Likewise.
	* math/libm-test.inc (lround_test, llround_test): Added test cases to
	detect aforementioned erroneous conditions.

1 files changed, 38 insertions, 19 deletions

diff --git a/sysdeps/powerpc/powerpc64/fpu/s_llround.S b/sysdeps/powerpc/powerpc64/fpu/s_llround.S
index d023b8f2c0..4134847536 100644
--- a/sysdeps/powerpc/powerpc64/fpu/s_llround.S
+++ b/sysdeps/powerpc/powerpc64/fpu/s_llround.S
@@ -1,5 +1,5 @@
 /* llround function.  PowerPC64 version.
-   Copyright (C) 2004, 2006 Free Software Foundation, Inc.
+   Copyright (C) 2004, 2006, 2007 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
@@ -21,13 +21,13 @@
 #include <math_ldbl_opt.h>
 
 	.section	".toc","aw"
-.LC0:	/* -0.0 */
-	.tc FD_00000000_0[TC],0x0000000000000000
+.LC0:	/* 2^52 */
+	.tc FD_43300000_0[TC],0x4330000000000000
 .LC1:	/* 0.5 */
 	.tc FD_3fe00000_0[TC],0x3fe0000000000000
 	.section	".text"
 	
-/* long long [r3] llround (float x [fp1])
+/* long long [r3] llround (double x [fp1])
    IEEE 1003.1 llround 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
@@ -35,26 +35,45 @@
    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.  */
+   to the integer value.
+
+   It is necessary to detect when x is (+-)0x1.fffffffffffffp-2
+   because adding +-0.5 in this case will cause an erroneous shift,
+   carry and round.  We simply return 0 if 0.5 > x > -0.5.  Likewise
+   if x is and odd number between +-(2^52 and 2^53-1) a shift and
+   carry will erroneously round if biased with +-0.5.  Therefore if x
+   is greater/less than +-2^52 we don't need to bias the number with
+   +-0.5.  */
 
 ENTRY (__llround)
 	CALL_MCOUNT 0
-	lfd	fp12,.LC0@toc(2)
-	lfd	fp10,.LC1@toc(2)
-	fcmpu	cr6,fp1,fp12	/* if (x > 0.0)  */
-	ble-	cr6,.L4
-	fadd	fp1,fp1,fp10	/* x+= 0.5;  */
-.L9:
-	fctidz	fp2,fp1		/* Convert To Integer DW llround toward 0.  */
-	stfd	fp2,-16(r1)
-	nop	/* Insure the following load is in a different dispatch group */
-	nop	/* to avoid pipe stall on POWER4&5.  */
+	lfd	fp9,.LC0@toc(2)	/* Load 2^52 into fpr9.  */
+	lfd	fp10,.LC1@toc(2)/* Load 0.5 into fpr10.  */
+	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  */
+	fcmpu	cr4,fp2,fp9	/* if |x| >= 2^52  */
+	fcmpu	cr3,fp1,fp12	/* x is negative? x < 0.0  */
+	blt-	cr6,.Lretzero	/* 0.5 > x < -0.5 so just return 0.  */
+	bge-	cr4,.Lnobias	/* 2^52 > x < -2^52 just convert with no bias.  */
+	fadd	fp3,fp2,fp10	/* |x|+=0.5 bias to prepare to round.  */
+	bge	cr3,.Lconvert	/* x is positive so don't negate x.  */
+	fnabs	fp3,fp3		/* -(|x|+=0.5)  */
+.Lconvert:
+	fctidz	fp4,fp3		/* Convert to Integer double word round toward 0.  */
+	stfd	fp4,-16(r1)
+	nop
+	nop
 	nop
-	ld	r3,-16(r1)
+	ld	r3,-16(r1)	/* Load return as integer.  */
+.Lout:
 	blr
-.L4:
-	fsub	fp1,fp1,fp10	/* x-= 0.5;  */
-	b	.L9
+.Lretzero:			/* 0.5 > x > -0.5  */
+	li	r3,0		/* return 0.  */
+	b	.Lout
+.Lnobias:
+	fmr	fp3,fp1
+	b	.Lconvert
 	END (__llround)
 
 strong_alias (__llround, __lround)