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GNU C Library master sources branch master updated. glibc-2.25-22-gedbbdb1

From: jsm28 at sourceware dot org
To: glibc-cvs at sourceware dot org
Date: 7 Feb 2017 17:16:06 -0000
Subject: GNU C Library master sources branch master updated. glibc-2.25-22-gedbbdb1
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The branch, master has been updated
       via  edbbdb185518008439221ed9db296ab31039d076 (commit)
      from  43ce02c6ec27d4e2d8f0ae327bbbeaba84060964 (commit)

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- Log -----------------------------------------------------------------
http://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commitdiff;h=edbbdb185518008439221ed9db296ab31039d076

commit edbbdb185518008439221ed9db296ab31039d076
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Tue Feb 7 17:15:47 2017 +0000

    Fix powf inaccuracy (bug 21112).
    
    Bug 21112 reports a case where powf is substantially inaccurate.  This
    results from a multiplication where cp_h*p_h is required to be exact,
    and p_h is masked to have only 12 leading nonzero bits in its
    mantissa, but the value of cp_h has the 13th bit nonzero, leading to
    inexact multiplication results in some cases that can result in large
    errors in the final result of powf.  This patch fixes this by using a
    value of cp_h correctly rounded to nearest to 12 bits, with a
    corresponding updated value of cp_l.
    
    Tested for x86_64 and x86.
    
    	[BZ #21112]
    	* sysdeps/ieee754/flt-32/e_powf.c (cp_h): Use value with trailing
    	12 bits zero.
    	(cp_l): Update for new value of cp_h.
    	* math/auto-libm-test-in: Add another test of pow.
    	* math/auto-libm-test-out-pow: Regenerated.

diff --git a/ChangeLog b/ChangeLog
index 4d667ad..037552d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2017-02-07  Joseph Myers  <joseph@codesourcery.com>
+
+	[BZ #21112]
+	* sysdeps/ieee754/flt-32/e_powf.c (cp_h): Use value with trailing
+	12 bits zero.
+	(cp_l): Update for new value of cp_h.
+	* math/auto-libm-test-in: Add another test of pow.
+	* math/auto-libm-test-out-pow: Regenerated.
+
 2017-02-07  Siddhesh Poyarekar  <siddhesh@sourceware.org>
 
 	* manual/contrib.texi: Fix typo.
diff --git a/math/auto-libm-test-in b/math/auto-libm-test-in
index 52272e8..58236ef 100644
--- a/math/auto-libm-test-in
+++ b/math/auto-libm-test-in
@@ -3749,6 +3749,7 @@ pow 0xf.fffffp+124 -0x5.b5b648p+0
 pow 0x1.430d4cp+0 0x5.0e462p+4
 pow 0x9.8b82ap-4 -0x1.99907ap+12
 pow 0xd.73035p-4 -0x1.47bb8p+8
+pow 0x1.059c76p+0 0x1.ff80bep+11
 
 sin 0
 sin -0
diff --git a/math/auto-libm-test-out-pow b/math/auto-libm-test-out-pow
index d2c662e..4a9f1fc 100644
--- a/math/auto-libm-test-out-pow
+++ b/math/auto-libm-test-out-pow
@@ -44146,3 +44146,28 @@ pow 0xd.73035p-4 -0x1.47bb8p+8
 = pow tonearest ibm128 0xd.73035p-4 -0x1.47bb8p+8 : 0x4.523987c590d3192757b32fb92cp+80 : inexact-ok
 = pow towardzero ibm128 0xd.73035p-4 -0x1.47bb8p+8 : 0x4.523987c590d3192757b32fb92cp+80 : inexact-ok
 = pow upward ibm128 0xd.73035p-4 -0x1.47bb8p+8 : 0x4.523987c590d3192757b32fb92ep+80 : inexact-ok
+pow 0x1.059c76p+0 0x1.ff80bep+11
+= pow downward binary32 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe55p+124 : inexact-ok
+= pow tonearest binary32 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe55p+124 : inexact-ok
+= pow towardzero binary32 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe55p+124 : inexact-ok
+= pow upward binary32 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe56p+124 : inexact-ok
+= pow downward binary64 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f98p+124 : inexact-ok
+= pow tonearest binary64 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f98p+124 : inexact-ok
+= pow towardzero binary64 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f98p+124 : inexact-ok
+= pow upward binary64 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38fap+124 : inexact-ok
+= pow downward intel96 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f9be6p+124 : inexact-ok
+= pow tonearest intel96 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f9be6p+124 : inexact-ok
+= pow towardzero intel96 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f9be6p+124 : inexact-ok
+= pow upward intel96 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f9be7p+124 : inexact-ok
+= pow downward m68k96 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f9be6p+124 : inexact-ok
+= pow tonearest m68k96 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f9be6p+124 : inexact-ok
+= pow towardzero m68k96 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f9be6p+124 : inexact-ok
+= pow upward m68k96 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f9be7p+124 : inexact-ok
+= pow downward binary128 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f9be648255c105d56p+124 : inexact-ok
+= pow tonearest binary128 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f9be648255c105d568p+124 : inexact-ok
+= pow towardzero binary128 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f9be648255c105d56p+124 : inexact-ok
+= pow upward binary128 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f9be648255c105d568p+124 : inexact-ok
+= pow downward ibm128 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f9be648255c105d4p+124 : inexact-ok
+= pow tonearest ibm128 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f9be648255c105d4p+124 : inexact-ok
+= pow towardzero ibm128 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f9be648255c105d4p+124 : inexact-ok
+= pow upward ibm128 0x1.059c76p+0 0xf.fc05fp+8 : 0xf.ffe5535a38f9be648255c105d8p+124 : inexact-ok
diff --git a/sysdeps/ieee754/flt-32/e_powf.c b/sysdeps/ieee754/flt-32/e_powf.c
index d9470f1..13b49de 100644
--- a/sysdeps/ieee754/flt-32/e_powf.c
+++ b/sysdeps/ieee754/flt-32/e_powf.c
@@ -43,8 +43,8 @@ lg2_h  =  6.93145752e-01, /* 0x3f317200 */
 lg2_l  =  1.42860654e-06, /* 0x35bfbe8c */
 ovt =  4.2995665694e-08, /* -(128-log2(ovfl+.5ulp)) */
 cp    =  9.6179670095e-01, /* 0x3f76384f =2/(3ln2) */
-cp_h  =  9.6179199219e-01, /* 0x3f763800 =head of cp */
-cp_l  =  4.7017383622e-06, /* 0x369dc3a0 =tail of cp_h */
+cp_h  =  0xf.64p-4, /* cp high 12 bits.  */
+cp_l  =  -0x7.b11e3p-16, /* 2/(3ln2) - cp_h.  */
 ivln2    =  1.4426950216e+00, /* 0x3fb8aa3b =1/ln2 */
 ivln2_h  =  1.4426879883e+00, /* 0x3fb8aa00 =16b 1/ln2*/
 ivln2_l  =  7.0526075433e-06; /* 0x36eca570 =1/ln2 tail*/

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

Summary of changes:
 ChangeLog                       |    9 +++++++++
 math/auto-libm-test-in          |    1 +
 math/auto-libm-test-out-pow     |   25 +++++++++++++++++++++++++
 sysdeps/ieee754/flt-32/e_powf.c |    4 ++--
 4 files changed, 37 insertions(+), 2 deletions(-)


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