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Fix log2 (1) in round-downward mode (bug 17042).
As with other issues of this kind, bug 17042 is log2 (1) wrongly returning -0 instead of +0 in round-downward mode because of implementations effectively in terms of log1p (x - 1). This patch fixes the issue in the same way used for log and log10. Tested x86_64 and x86 and ulps updated accordingly. Also tested for mips64 to confirm a fix was needed for ldbl-128 and to validate that fix (also applied to ldbl-128ibm since that version of log2l is essentially the same as the ldbl-128 one). [BZ #17042] * sysdeps/i386/fpu/e_log2.S (__ieee754_log2): Take absolete value when x - 1 is zero. * sysdeps/i386/fpu/e_log2f.S (__ieee754_log2f): Likewise. * sysdeps/i386/fpu/e_log2l.S (__ieee754_log2l): Likewise. * sysdeps/ieee754/ldbl-128/e_log2l.c (__ieee754_log2l): Return 0.0L for an argument of 1.0L. * sysdeps/ieee754/ldbl-128ibm/e_log2l.c (__ieee754_log2l): Likewise. * sysdeps/x86_64/fpu/e_log2l.S (__ieee754_log2l): Take absolute value when x - 1 is zero. * math/libm-test.inc (log2_test): Use ALL_RM_TEST. * sysdeps/i386/fpu/libm-test-ulps: Update. * sysdeps/x86_64/fpu/libm-test-ulps: Likewise.
This commit is contained in:
Joseph Myers
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17
ChangeLog
17
ChangeLog
@ -1,3 +1,20 @@
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2014-06-10 Joseph Myers <joseph@codesourcery.com>
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[BZ #17042]
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* sysdeps/i386/fpu/e_log2.S (__ieee754_log2): Take absolete value
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when x - 1 is zero.
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* sysdeps/i386/fpu/e_log2f.S (__ieee754_log2f): Likewise.
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* sysdeps/i386/fpu/e_log2l.S (__ieee754_log2l): Likewise.
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* sysdeps/ieee754/ldbl-128/e_log2l.c (__ieee754_log2l): Return
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0.0L for an argument of 1.0L.
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* sysdeps/ieee754/ldbl-128ibm/e_log2l.c (__ieee754_log2l):
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Likewise.
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* sysdeps/x86_64/fpu/e_log2l.S (__ieee754_log2l): Take absolute
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value when x - 1 is zero.
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* math/libm-test.inc (log2_test): Use ALL_RM_TEST.
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* sysdeps/i386/fpu/libm-test-ulps: Update.
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* sysdeps/x86_64/fpu/libm-test-ulps: Likewise.
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2014-06-09 Bernard Ogden <bernie.ogden@linaro.org>
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[BZ #15119]
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2
NEWS
2
NEWS
@ -19,7 +19,7 @@ Version 2.20
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16791, 16796, 16799, 16800, 16815, 16823, 16824, 16831, 16838, 16849,
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16854, 16876, 16877, 16878, 16882, 16885, 16888, 16890, 16912, 16915,
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16916, 16917, 16922, 16927, 16928, 16932, 16943, 16958, 16965, 16966,
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16967, 16977, 16978, 16984, 16990, 17009.
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16967, 16977, 16978, 16984, 16990, 17009, 17042.
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* The minimum Linux kernel version that this version of the GNU C Library
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can be used with is 2.6.32.
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@ -7840,9 +7840,7 @@ static const struct test_f_f_data log2_test_data[] =
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static void
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log2_test (void)
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{
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START (log2, 0);
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RUN_TEST_LOOP_f_f (log2, log2_test_data, );
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END;
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ALL_RM_TEST (log2, 0, log2_test_data, RUN_TEST_LOOP_f_f, END);
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}
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@ -47,7 +47,13 @@ ENTRY(__ieee754_log2)
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fnstsw // x-1 : x : 1
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andb $0x45, %ah
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jz 2f
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fstp %st(1) // x-1 : 1
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fxam
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fnstsw
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andb $0x45, %ah
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cmpb $0x40, %ah
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jne 5f
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fabs // log2(1) is +0 in all rounding modes.
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5: fstp %st(1) // x-1 : 1
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fyl2xp1 // log(x)
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ret
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@ -47,7 +47,13 @@ ENTRY(__ieee754_log2f)
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fnstsw // x-1 : x : 1
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andb $0x45, %ah
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jz 2f
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fstp %st(1) // x-1 : 1
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fxam
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fnstsw
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andb $0x45, %ah
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cmpb $0x40, %ah
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jne 5f
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fabs // log2(1) is +0 in all rounding modes.
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5: fstp %st(1) // x-1 : 1
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fyl2xp1 // log(x)
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ret
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@ -47,7 +47,13 @@ ENTRY(__ieee754_log2l)
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fnstsw // x-1 : x : 1
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andb $0x45, %ah
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jz 2f
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fstp %st(1) // x-1 : 1
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fxam
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fnstsw
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andb $0x45, %ah
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cmpb $0x40, %ah
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jne 5f
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fabs // log2(1) is +0 in all rounding modes.
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5: fstp %st(1) // x-1 : 1
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fyl2xp1 // log(x)
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ret
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@ -1588,6 +1588,22 @@ ifloat: 1
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ildouble: 1
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ldouble: 1
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Function: "log2_towardzero":
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double: 1
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float: 1
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idouble: 1
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ifloat: 1
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ildouble: 1
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ldouble: 1
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Function: "log2_upward":
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double: 1
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float: 1
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idouble: 1
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ifloat: 1
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ildouble: 1
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ldouble: 1
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Function: "log_downward":
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ildouble: 1
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ldouble: 1
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@ -188,6 +188,9 @@ __ieee754_log2l (x)
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if (hx >= 0x7fff000000000000LL)
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return (x + x);
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if (x == 1.0L)
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return 0.0L;
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/* separate mantissa from exponent */
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/* Note, frexp is used so that denormal numbers
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@ -190,6 +190,9 @@ __ieee754_log2l (x)
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if (hx >= 0x7ff0000000000000LL)
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return (x + x);
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if (x == 1.0L)
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return 0.0L;
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/* separate mantissa from exponent */
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/* Note, frexp is used so that denormal numbers
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@ -45,7 +45,13 @@ ENTRY(__ieee754_log2l)
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fnstsw // x-1 : x : 1
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andb $0x45, %ah
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jz 2f
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fstp %st(1) // x-1 : 1
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fxam
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fnstsw
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andb $0x45, %ah
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cmpb $0x40, %ah
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jne 5f
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fabs // log2(1) is +0 in all rounding modes.
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5: fstp %st(1) // x-1 : 1
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fyl2xp1 // log(x)
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ret
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@ -1665,6 +1665,28 @@ ifloat: 1
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ildouble: 1
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ldouble: 1
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Function: "log2_downward":
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double: 2
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float: 2
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idouble: 2
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ifloat: 2
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Function: "log2_towardzero":
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double: 1
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float: 1
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idouble: 1
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ifloat: 1
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ildouble: 1
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ldouble: 1
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Function: "log2_upward":
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double: 2
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float: 2
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idouble: 2
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ifloat: 2
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ildouble: 1
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ldouble: 1
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Function: "log_downward":
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float: 1
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ifloat: 1
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