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authorJoseph Myers <joseph@codesourcery.com>2015-10-05 22:53:50 +0000
committerJoseph Myers <joseph@codesourcery.com>2015-10-05 22:54:50 +0000
commitcec7d28af8ccb40dbf82d99efa13a040b31b9387 (patch)
tree712f63f528c5cb98381cdc15e063558d72667f35 /sysdeps
parenta8133e197ec852cac46132efeeefae14489031f0 (diff)
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Fix ldbl-96 lroundl just below powers of 2 (bug 19071).
The ldbl-96 version of lroundl is incorrect for systems with 64-bit long when the argument's absolute value is just below a power of 2, 2^32 or more, and rounds up to the next integer; in such cases, it returns 0. The problem is incrementing the high part of the mantissa loses the high bit of the value (which is not an issue for any other floating-point format, and is handled specially in lround when the bit corresponding to 0.5 was in the high part rather than the low part). This patch fixes this in a similar way to that used in llroundl: storing the high part in an unsigned long variable before incrementing it, so problems cannot occur in the case when this code is reachable. I improved test coverage for both lround and llround by making them use the same test inputs (appropriately conditioned on the size of long in the lround case) - complete with the same comments, to make comparison as easy as possible. (This test coverage improvement was how I found the lroundl bug.) Tested for x86_64 and x86. [BZ #19071] * sysdeps/ieee754/ldbl-96/s_lroundl.c (__lroundl): Use unsigned long int variable to store possibly incremented high part of mantissa. * math/libm-test.inc (lround_test_data): Add tests used for llround. Use [LONG_MAX > 0x7fffffff] consistently as condition for tests requiring 64-bit long. Do not condition tests on [TEST_FLOAT] unnecessarily. (llround_test_data): Add tests used for lround. Add another expectation for the "inexact" exception. Do not condition tests on [TEST_FLOAT] unnecessarily.
Diffstat (limited to 'sysdeps')
-rw-r--r--sysdeps/ieee754/ldbl-96/s_lroundl.c8
1 files changed, 5 insertions, 3 deletions
diff --git a/sysdeps/ieee754/ldbl-96/s_lroundl.c b/sysdeps/ieee754/ldbl-96/s_lroundl.c
index e34edd3..7a59835 100644
--- a/sysdeps/ieee754/ldbl-96/s_lroundl.c
+++ b/sysdeps/ieee754/ldbl-96/s_lroundl.c
@@ -58,13 +58,15 @@ __lroundl (long double x)
else
{
u_int32_t j = i1 + (0x80000000 >> (j0 - 31));
+ unsigned long int ures = i0;
+
if (j < i1)
- ++i0;
+ ++ures;
if (j0 == 31)
- result = (long int) i0;
+ result = ures;
else
- result = ((long int) i0 << (j0 - 31)) | (j >> (63 - j0));
+ result = (ures << (j0 - 31)) | (j >> (63 - j0));
}
}
else