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Fix powf inaccuracy (bug 18956).
The flt-32 version of powf can be inaccurate because of bugs in the extra-precision calculation of (x-1)/(x+1) or (x-1.5)/(x+1.5) as part of calculating log(x) with extra precision: a constant used (as part of adding 1 or 1.5 through integer arithmetic) is incorrect, and then the code fails to mask a computed high part before using it in arithmetic that relies on s_h*t_h being exactly representable. This patch fixes these bugs. Tested for x86_64 and x86. x86_64 ulps for powf removed and regenerated to reflect reduced ulps from the increased accuracy for existing tests. [BZ #18956] * sysdeps/ieee754/flt-32/e_powf.c (__ieee754_powf): Add 0x00400000 not 0x0040000 for high bit of mantissa. Mask with 0xfffff000 when extracting high part. * math/auto-libm-test-in: Add another test of pow. * math/auto-libm-test-out: Regenerated. * sysdeps/x86_64/fpu/libm-test-ulps: Update.
This commit is contained in:
Joseph Myers
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10
ChangeLog
10
ChangeLog
@ -1,3 +1,13 @@
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2015-09-26 Joseph Myers <joseph@codesourcery.com>
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[BZ #18956]
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* sysdeps/ieee754/flt-32/e_powf.c (__ieee754_powf): Add 0x00400000
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not 0x0040000 for high bit of mantissa. Mask with 0xfffff000 when
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extracting high part.
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* math/auto-libm-test-in: Add another test of pow.
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* math/auto-libm-test-out: Regenerated.
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* sysdeps/x86_64/fpu/libm-test-ulps: Update.
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2015-09-25 Joseph Myers <joseph@codesourcery.com>
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[BZ #18825]
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4
NEWS
4
NEWS
@ -15,8 +15,8 @@ Version 2.23
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18084, 18086, 18240, 18265, 18370, 18421, 18480, 18525, 18595, 18610,
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18618, 18647, 18661, 18674, 18675, 18681, 18757, 18778, 18781, 18787,
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18789, 18790, 18795, 18796, 18803, 18820, 18823, 18824, 18825, 18857,
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18863, 18870, 18872, 18873, 18875, 18887, 18921, 18951, 18952, 18961,
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18966, 18967, 18970, 18977, 18980, 18981, 19003.
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18863, 18870, 18872, 18873, 18875, 18887, 18921, 18951, 18952, 18956,
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18961, 18966, 18967, 18970, 18977, 18980, 18981, 19003.
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* The obsolete header <regexp.h> has been removed. Programs that require
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this header must be updated to use <regex.h> instead.
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@ -3219,6 +3219,7 @@ pow 0x1.ce78f2p+0 -0x2.7f1f78p+4
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pow 0xf.fffffp+124 -0x5.b5b648p+0
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pow 0x1.430d4cp+0 0x5.0e462p+4
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pow 0x9.8b82ap-4 -0x1.99907ap+12
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pow 0xd.73035p-4 -0x1.47bb8p+8
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sin 0
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sin -0
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@ -226489,6 +226489,31 @@ pow 0x9.8b82ap-4 -0x1.99907ap+12
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= pow tonearest ldbl-128ibm 0x9.8b82ap-4L -0x1.99907ap+12L : plus_infty : inexact-ok overflow errno-erange
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= pow towardzero ldbl-128ibm 0x9.8b82ap-4L -0x1.99907ap+12L : 0xf.ffffffffffffbffffffffffffcp+1020L : inexact-ok overflow errno-erange-ok
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= pow upward ldbl-128ibm 0x9.8b82ap-4L -0x1.99907ap+12L : plus_infty : inexact-ok overflow errno-erange
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pow 0xd.73035p-4 -0x1.47bb8p+8
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= pow downward flt-32 0xd.73035p-4f -0x1.47bb8p+8f : 0x4.52398p+80f : inexact-ok
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= pow tonearest flt-32 0xd.73035p-4f -0x1.47bb8p+8f : 0x4.523988p+80f : inexact-ok
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= pow towardzero flt-32 0xd.73035p-4f -0x1.47bb8p+8f : 0x4.52398p+80f : inexact-ok
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= pow upward flt-32 0xd.73035p-4f -0x1.47bb8p+8f : 0x4.523988p+80f : inexact-ok
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= pow downward dbl-64 0xd.73035p-4 -0x1.47bb8p+8 : 0x4.523987c590d3p+80 : inexact-ok
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= pow tonearest dbl-64 0xd.73035p-4 -0x1.47bb8p+8 : 0x4.523987c590d3p+80 : inexact-ok
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= pow towardzero dbl-64 0xd.73035p-4 -0x1.47bb8p+8 : 0x4.523987c590d3p+80 : inexact-ok
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= pow upward dbl-64 0xd.73035p-4 -0x1.47bb8p+8 : 0x4.523987c590d34p+80 : inexact-ok
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= pow downward ldbl-96-intel 0xd.73035p-4L -0x1.47bb8p+8L : 0x4.523987c590d3192p+80L : inexact-ok
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= pow tonearest ldbl-96-intel 0xd.73035p-4L -0x1.47bb8p+8L : 0x4.523987c590d31928p+80L : inexact-ok
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= pow towardzero ldbl-96-intel 0xd.73035p-4L -0x1.47bb8p+8L : 0x4.523987c590d3192p+80L : inexact-ok
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= pow upward ldbl-96-intel 0xd.73035p-4L -0x1.47bb8p+8L : 0x4.523987c590d31928p+80L : inexact-ok
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= pow downward ldbl-96-m68k 0xd.73035p-4L -0x1.47bb8p+8L : 0x4.523987c590d3192p+80L : inexact-ok
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= pow tonearest ldbl-96-m68k 0xd.73035p-4L -0x1.47bb8p+8L : 0x4.523987c590d31928p+80L : inexact-ok
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= pow towardzero ldbl-96-m68k 0xd.73035p-4L -0x1.47bb8p+8L : 0x4.523987c590d3192p+80L : inexact-ok
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= pow upward ldbl-96-m68k 0xd.73035p-4L -0x1.47bb8p+8L : 0x4.523987c590d31928p+80L : inexact-ok
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= pow downward ldbl-128 0xd.73035p-4L -0x1.47bb8p+8L : 0x4.523987c590d3192757b32fb92c7p+80L : inexact-ok
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= pow tonearest ldbl-128 0xd.73035p-4L -0x1.47bb8p+8L : 0x4.523987c590d3192757b32fb92c74p+80L : inexact-ok
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= pow towardzero ldbl-128 0xd.73035p-4L -0x1.47bb8p+8L : 0x4.523987c590d3192757b32fb92c7p+80L : inexact-ok
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= pow upward ldbl-128 0xd.73035p-4L -0x1.47bb8p+8L : 0x4.523987c590d3192757b32fb92c74p+80L : inexact-ok
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= pow downward ldbl-128ibm 0xd.73035p-4L -0x1.47bb8p+8L : 0x4.523987c590d3192757b32fb92cp+80L : inexact-ok
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= pow tonearest ldbl-128ibm 0xd.73035p-4L -0x1.47bb8p+8L : 0x4.523987c590d3192757b32fb92cp+80L : inexact-ok
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= pow towardzero ldbl-128ibm 0xd.73035p-4L -0x1.47bb8p+8L : 0x4.523987c590d3192757b32fb92cp+80L : inexact-ok
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= pow upward ldbl-128ibm 0xd.73035p-4L -0x1.47bb8p+8L : 0x4.523987c590d3192757b32fb92ep+80L : inexact-ok
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sin 0
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= sin downward flt-32 0x0p+0f : 0x0p+0f : inexact-ok
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= sin tonearest flt-32 0x0p+0f : 0x0p+0f : inexact-ok
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@ -166,7 +166,9 @@ __ieee754_powf(float x, float y)
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GET_FLOAT_WORD(is,s_h);
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SET_FLOAT_WORD(s_h,is&0xfffff000);
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/* t_h=ax+bp[k] High */
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SET_FLOAT_WORD(t_h,((ix>>1)|0x20000000)+0x0040000+(k<<21));
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SET_FLOAT_WORD (t_h,
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((((ix>>1)|0x20000000)+0x00400000+(k<<21))
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& 0xfffff000));
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t_l = ax - (t_h-bp[k]);
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s_l = v*((u-s_h*t_h)-s_h*t_l);
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/* compute log(ax) */
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@ -1966,8 +1966,8 @@ Function: "log_vlen8_avx2":
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float: 2
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Function: "pow":
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float: 3
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ifloat: 3
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float: 1
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ifloat: 1
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ildouble: 1
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ldouble: 1
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@ -2003,25 +2003,25 @@ ldouble: 2
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Function: "pow_downward":
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double: 1
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float: 4
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float: 1
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idouble: 1
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ifloat: 4
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ifloat: 1
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ildouble: 4
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ldouble: 4
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Function: "pow_towardzero":
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double: 1
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float: 8
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float: 1
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idouble: 1
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ifloat: 8
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ifloat: 1
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ildouble: 1
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ldouble: 1
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Function: "pow_upward":
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double: 1
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float: 8
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float: 1
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idouble: 1
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ifloat: 8
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ifloat: 1
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ildouble: 2
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ldouble: 2
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