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Fix log2 (1) in round-downward mode (bug 17042).

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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
2014-06-10 12:07:15 +00:00
parent 2c3520d98d
commit f8ba1b5654
11 changed files with 91 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
math/libm-test.inc
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@ -7840,9 +7840,7 @@ static const struct test_f_f_data log2_test_data[] =
static void
log2_test (void)
{
START (log2, 0);
RUN_TEST_LOOP_f_f (log2, log2_test_data, );
END;
ALL_RM_TEST (log2, 0, log2_test_data, RUN_TEST_LOOP_f_f, END);
}