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Add some tests for double-rounding bugs in fma().

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This commit is contained in:
David Schultz 2011-10-15 05:26:16 +00:00
parent b052ec9065
commit 9c7781b7a3
1 changed files with 54 additions and 1 deletions
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55
tools/regression/lib/msun/test-fma.c
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@ -364,13 +364,63 @@ test_accuracy(void)
#endif
}
static void
test_double_rounding(void)
{
/*
* a = 0x1.8000000000001p0
* b = 0x1.8000000000001p0
* c = -0x0.0000000000000000000000000080...1p+1
* a * b = 0x1.2000000000001800000000000080p+1
*
* The correct behavior is to round DOWN to 0x1.2000000000001p+1 in
* round-to-nearest mode. An implementation that computes a*b+c in
* double+double precision, however, will get 0x1.20000000000018p+1,
* and then round UP.
*/
fesetround(FE_TONEAREST);
test(fma, 0x1.8000000000001p0, 0x1.8000000000001p0,
-0x1.0000000000001p-104, 0x1.2000000000001p+1,
ALL_STD_EXCEPT, FE_INEXACT);
fesetround(FE_DOWNWARD);
test(fma, 0x1.8000000000001p0, 0x1.8000000000001p0,
-0x1.0000000000001p-104, 0x1.2000000000001p+1,
ALL_STD_EXCEPT, FE_INEXACT);
fesetround(FE_UPWARD);
test(fma, 0x1.8000000000001p0, 0x1.8000000000001p0,
-0x1.0000000000001p-104, 0x1.2000000000002p+1,
ALL_STD_EXCEPT, FE_INEXACT);
fesetround(FE_TONEAREST);
test(fmaf, 0x1.800002p+0, 0x1.800002p+0, -0x1.000002p-46, 0x1.200002p+1,
ALL_STD_EXCEPT, FE_INEXACT);
fesetround(FE_DOWNWARD);
test(fmaf, 0x1.800002p+0, 0x1.800002p+0, -0x1.000002p-46, 0x1.200002p+1,
ALL_STD_EXCEPT, FE_INEXACT);
fesetround(FE_UPWARD);
test(fmaf, 0x1.800002p+0, 0x1.800002p+0, -0x1.000002p-46, 0x1.200004p+1,
ALL_STD_EXCEPT, FE_INEXACT);
fesetround(FE_TONEAREST);
#if LDBL_MANT_DIG == 64
test(fmal, 0x1.4p+0L, 0x1.0000000000000004p+0L, 0x1p-128L,
0x1.4000000000000006p+0L, ALL_STD_EXCEPT, FE_INEXACT);
#elif LDBL_MANT_DIG == 113
/* XXX untested test */
test(fmal, 0x1.4p+0L, 0x1.0000000000000000000000000002p+0L, 0x1p-224L,
0x1.4000000000000000000000000003p+0L, ALL_STD_EXCEPT, FE_INEXACT);
#endif
}
int
main(int argc, char *argv[])
{
int rmodes[] = { FE_TONEAREST, FE_UPWARD, FE_DOWNWARD, FE_TOWARDZERO };
int i;
printf("1..18\n");
printf("1..19\n");
for (i = 0; i < 4; i++) {
fesetround(rmodes[i]);
@ -404,6 +454,9 @@ main(int argc, char *argv[])
test_accuracy();
printf("ok 18 - fma accuracy\n");
test_double_rounding();
printf("ok 19 - fma double rounding\n");
/*
* TODO:
* - Tests for subnormals