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Fix ldbl-128ibm ilogbl near powers of 2 (bug 18029).

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The ldbl-128ibm implementation of ilogbl produces incorrect results
when the high part of the argument is a power of 2 and the low part a
nonzero number with the opposite sign (and so the returned exponent
should be 1 less than that of the high part).  For example, ilogbl
(0x1.ffffffffffffffp1L) returns 2 but should return 1.  (This is
similar to (fixed) bug 16740 for frexpl, and bug 18030 for logbl.)
This patch adds checks for that case.

Tested for powerpc.

	[BZ #18029]
	* sysdeps/ieee754/ldbl-128ibm/e_ilogbl.c (__ieee754_ilogbl):
	Adjust exponent of power of 2 down when low part has opposite
	sign.
	* math/libm-test.inc (ilogb_test_data): Add more tests.
This commit is contained in:
Joseph Myers
2015-02-26 12:57:21 +00:00
parent 23d43090e0
commit 524ae9ea2e
4 changed files with 33 additions and 5 deletions
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5
math/libm-test.inc
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@ -7219,6 +7219,11 @@ static const struct test_f_i_data ilogb_test_data[] =
TEST_f_i (ilogb, 1024, 10, NO_INEXACT_EXCEPTION),
TEST_f_i (ilogb, -2000, 10, NO_INEXACT_EXCEPTION),
#if defined TEST_LDOUBLE && LDBL_MANT_DIG >= 57
TEST_f_i (ilogb, 0x1.ffffffffffffffp1L, 1, NO_INEXACT_EXCEPTION),
TEST_f_i (ilogb, -0x1.ffffffffffffffp1L, 1, NO_INEXACT_EXCEPTION),
#endif
/* ilogb (0.0) == FP_ILOGB0 plus invalid exception */
TEST_f_i (ilogb, 0.0, FP_ILOGB0, NO_INEXACT_EXCEPTION|INVALID_EXCEPTION|ERRNO_EDOM),
/* ilogb (qNaN) == FP_ILOGBNAN plus invalid exception */