GNU C Library master sources branch master updated. glibc-2.21-73-g95c2623

[jsm28 at sourceware dot org]

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http://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commitdiff;h=95c26233a1c7dd73a852a4f3bffd2d2eeba5e2fd

commit 95c26233a1c7dd73a852a4f3bffd2d2eeba5e2fd
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Fri Feb 13 16:20:36 2015 +0000

    Fix powerpc software sqrtf (bug 17967).
    
    Similarly to sqrt in
    <https://sourceware.org/ml/libc-alpha/2015-02/msg00353.html>, the
    powerpc sqrtf implementation for when _ARCH_PPCSQ is not defined also
    relies on a * b + c being contracted into a fused multiply-add.
    Although this contraction is not explicitly disabled for e_sqrtf.c, it
    still seems appropriate to make the file explicit about its
    requirements by using __builtin_fmaf; this patch does so.
    Furthermore, it turns out that doing so fixes the observed inaccuracy
    and missing exceptions (that is, that without explicit __builtin_fmaf
    usage, it was not being compiled as intended).
    
    Tested for powerpc32 (hard float).
    
    	[BZ #17967]
    	* sysdeps/powerpc/fpu/e_sqrtf.c (__slow_ieee754_sqrtf): Use
    	__builtin_fmaf instead of relying on contraction of a * b + c.

diff --git a/ChangeLog b/ChangeLog
index 821da1d..50adb3c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2015-02-13  Joseph Myers  <joseph@codesourcery.com>
+
+	[BZ #17967]
+	* sysdeps/powerpc/fpu/e_sqrtf.c (__slow_ieee754_sqrtf): Use
+	__builtin_fmaf instead of relying on contraction of a * b + c.
+
 2015-02-12  J William Piggott  <elseifthen@gmx.com>
 
 	[BZ #17969]
diff --git a/NEWS b/NEWS
index f6f34e8..b95f5e6 100644
--- a/NEWS
+++ b/NEWS
@@ -10,7 +10,7 @@ Version 2.22
 * The following bugs are resolved with this release:
 
   4719, 15467, 15790, 16560, 17912, 17932, 17944, 17949, 17964, 17965,
-  17969.
+  17967, 17969.
 
 Version 2.21
 
diff --git a/sysdeps/powerpc/fpu/e_sqrtf.c b/sysdeps/powerpc/fpu/e_sqrtf.c
index 034b6f5..a684cf9 100644
--- a/sysdeps/powerpc/fpu/e_sqrtf.c
+++ b/sysdeps/powerpc/fpu/e_sqrtf.c
@@ -87,26 +87,28 @@ __slow_ieee754_sqrtf (float x)
 	  /* Here we have three Newton-Raphson iterations each of a
 	     division and a square root and the remainder of the
 	     argument reduction, all interleaved.   */
-	  sd = -(sg * sg - sx);
+	  sd = -__builtin_fmaf (sg, sg, -sx);
 	  fsgi = (xi + 0x40000000) >> 1 & 0x7f800000;
 	  sy2 = sy + sy;
-	  sg = sy * sd + sg;	/* 16-bit approximation to sqrt(sx). */
-	  e = -(sy * sg - almost_half);
+	  sg = __builtin_fmaf (sy, sd, sg);	/* 16-bit approximation to
+						   sqrt(sx). */
+	  e = -__builtin_fmaf (sy, sg, -almost_half);
 	  SET_FLOAT_WORD (fsg, fsgi);
-	  sd = -(sg * sg - sx);
-	  sy = sy + e * sy2;
+	  sd = -__builtin_fmaf (sg, sg, -sx);
+	  sy = __builtin_fmaf (e, sy2, sy);
 	  if ((xi & 0x7f800000) == 0)
 	    goto denorm;
 	  shx = sx * fsg;
-	  sg = sg + sy * sd;	/* 32-bit approximation to sqrt(sx),
-				   but perhaps rounded incorrectly.  */
+	  sg = __builtin_fmaf (sy, sd, sg);	/* 32-bit approximation to
+						   sqrt(sx), but perhaps
+						   rounded incorrectly.  */
 	  sy2 = sy + sy;
 	  g = sg * fsg;
-	  e = -(sy * sg - almost_half);
-	  d = -(g * sg - shx);
-	  sy = sy + e * sy2;
+	  e = -__builtin_fmaf (sy, sg, -almost_half);
+	  d = -__builtin_fmaf (g, sg, -shx);
+	  sy = __builtin_fmaf (e, sy2, sy);
 	  fesetenv_register (fe);
-	  return g + sy * d;
+	  return __builtin_fmaf (sy, d, g);
 	denorm:
 	  /* For denormalised numbers, we normalise, calculate the
 	     square root, and return an adjusted result.  */

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                     |    6 ++++++
 NEWS                          |    2 +-
 sysdeps/powerpc/fpu/e_sqrtf.c |   24 +++++++++++++-----------
 3 files changed, 20 insertions(+), 12 deletions(-)


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