aboutsummaryrefslogtreecommitdiff
diff options
context:
space:
mode:
-rw-r--r--ChangeLog7
-rw-r--r--math/libm-test.inc10
-rw-r--r--sysdeps/ieee754/dbl-64/s_fma.c103
3 files changed, 105 insertions, 15 deletions
diff --git a/ChangeLog b/ChangeLog
index a6af960..62ba40b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2010-10-14 Jakub Jelinek <jakub@redhat.com>
+
+ [BZ #3268]
+ * math/libm-test.inc (fma_test): Add some more tests.
+ * sysdeps/ieee754/dbl-64/s_fma.c (__fma): Handle underflows
+ correctly.
+
2010-10-15 Andreas Schwab <schwab@redhat.com>
* scripts/data/localplt-s390-linux-gnu.data: New file.
diff --git a/math/libm-test.inc b/math/libm-test.inc
index 34c4fa9..1bec476 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -2808,6 +2808,16 @@ fma_test (void)
TEST_fff_f (fma, 0x1.fffffffffffffp+1023, 0x1.001p+0, -0x1.fffffffffffffp+1023, 0x1.fffffffffffffp+1011);
TEST_fff_f (fma, -0x1.fffffffffffffp+1023, 0x1.fffffffffffffp+0, 0x1.fffffffffffffp+1023, -0x1.ffffffffffffdp+1023);
TEST_fff_f (fma, 0x1.fffffffffffffp+1023, 2.0, -0x1.fffffffffffffp+1023, 0x1.fffffffffffffp+1023);
+ TEST_fff_f (fma, 0x1.6a09e667f3bccp-538, 0x1.6a09e667f3bccp-538, 0.0, 0.0);
+ TEST_fff_f (fma, 0x1.deadbeef2feedp-495, 0x1.deadbeef2feedp-495, -0x1.bf86a5786a574p-989, 0x0.0000042625a1fp-1022);
+ TEST_fff_f (fma, 0x1.deadbeef2feedp-503, 0x1.deadbeef2feedp-503, -0x1.bf86a5786a574p-1005, 0x0.0000000004262p-1022);
+ TEST_fff_f (fma, 0x1p-537, 0x1p-538, 0x1p-1074, 0x0.0000000000002p-1022);
+ TEST_fff_f (fma, 0x1.7fffff8p-968, 0x1p-106, 0x0.000001p-1022, 0x0.0000010000001p-1022);
+ TEST_fff_f (fma, 0x1.4000004p-967, 0x1p-106, 0x0.000001p-1022, 0x0.0000010000003p-1022);
+ TEST_fff_f (fma, 0x1.4p-967, -0x1p-106, -0x0.000001p-1022, -0x0.0000010000002p-1022);
+ TEST_fff_f (fma, -0x1.19cab66d73e17p-959, 0x1.c7108a8c5ff51p-107, -0x0.80b0ad65d9b64p-1022, -0x0.80b0ad65d9d59p-1022);
+ TEST_fff_f (fma, -0x1.d2eaed6e8e9d3p-979, -0x1.4e066c62ac9ddp-63, -0x0.9245e6b003454p-1022, -0x0.9245c09c5fb5dp-1022);
+ TEST_fff_f (fma, 0x1.153d650bb9f06p-907, 0x1.2d01230d48407p-125, -0x0.b278d5acfc3cp-1022, -0x0.b22757123bbe9p-1022);
#endif
END (fma);
diff --git a/sysdeps/ieee754/dbl-64/s_fma.c b/sysdeps/ieee754/dbl-64/s_fma.c
index ca7300c..911682e 100644
--- a/sysdeps/ieee754/dbl-64/s_fma.c
+++ b/sysdeps/ieee754/dbl-64/s_fma.c
@@ -39,15 +39,20 @@ __fma (double x, double y, double z)
>= 0x7ff + IEEE754_DOUBLE_BIAS - DBL_MANT_DIG, 0)
|| __builtin_expect (u.ieee.exponent >= 0x7ff - DBL_MANT_DIG, 0)
|| __builtin_expect (v.ieee.exponent >= 0x7ff - DBL_MANT_DIG, 0)
- || __builtin_expect (w.ieee.exponent >= 0x7ff - DBL_MANT_DIG, 0))
+ || __builtin_expect (w.ieee.exponent >= 0x7ff - DBL_MANT_DIG, 0)
+ || __builtin_expect (u.ieee.exponent + v.ieee.exponent
+ <= IEEE754_DOUBLE_BIAS + DBL_MANT_DIG, 0))
{
- /* If x or y or z is Inf/NaN or if fma will certainly overflow,
+ /* If x or y or z is Inf/NaN, or if fma will certainly overflow,
+ or if x * y is less than half of DBL_DENORM_MIN,
compute as x * y + z. */
if (u.ieee.exponent == 0x7ff
|| v.ieee.exponent == 0x7ff
|| w.ieee.exponent == 0x7ff
|| u.ieee.exponent + v.ieee.exponent
- > 0x7ff + IEEE754_DOUBLE_BIAS)
+ > 0x7ff + IEEE754_DOUBLE_BIAS
+ || u.ieee.exponent + v.ieee.exponent
+ < IEEE754_DOUBLE_BIAS - DBL_MANT_DIG - 2)
return x * y + z;
if (u.ieee.exponent + v.ieee.exponent
>= 0x7ff + IEEE754_DOUBLE_BIAS - DBL_MANT_DIG)
@@ -87,7 +92,7 @@ __fma (double x, double y, double z)
else
v.d *= 0x1p53;
}
- else
+ else if (v.ieee.exponent >= 0x7ff - DBL_MANT_DIG)
{
v.ieee.exponent -= DBL_MANT_DIG;
if (u.ieee.exponent)
@@ -95,6 +100,24 @@ __fma (double x, double y, double z)
else
u.d *= 0x1p53;
}
+ else /* if (u.ieee.exponent + v.ieee.exponent
+ <= IEEE754_DOUBLE_BIAS + DBL_MANT_DIG) */
+ {
+ if (u.ieee.exponent > v.ieee.exponent)
+ u.ieee.exponent += 2 * DBL_MANT_DIG;
+ else
+ v.ieee.exponent += 2 * DBL_MANT_DIG;
+ if (w.ieee.exponent <= 4 * DBL_MANT_DIG + 4)
+ {
+ if (w.ieee.exponent)
+ w.ieee.exponent += 2 * DBL_MANT_DIG;
+ else
+ w.d *= 0x1p106;
+ adjust = -1;
+ }
+ /* Otherwise x * y should just affect inexact
+ and nothing else. */
+ }
x = u.d;
y = v.d;
z = w.d;
@@ -123,18 +146,68 @@ __fma (double x, double y, double z)
fesetround (FE_TOWARDZERO);
/* Perform m2 + a2 addition with round to odd. */
u.d = a2 + m2;
- if ((u.ieee.mantissa1 & 1) == 0 && u.ieee.exponent != 0x7ff)
- u.ieee.mantissa1 |= fetestexcept (FE_INEXACT) != 0;
- feupdateenv (&env);
-
- /* Add that to a1. */
- a1 = a1 + u.d;
- /* And adjust exponent if needed. */
- if (__builtin_expect (adjust, 0))
- a1 *= 0x1p53;
-
- return a1;
+ if (__builtin_expect (adjust == 0, 1))
+ {
+ if ((u.ieee.mantissa1 & 1) == 0 && u.ieee.exponent != 0x7ff)
+ u.ieee.mantissa1 |= fetestexcept (FE_INEXACT) != 0;
+ feupdateenv (&env);
+ /* Result is a1 + u.d. */
+ return a1 + u.d;
+ }
+ else if (__builtin_expect (adjust > 0, 1))
+ {
+ if ((u.ieee.mantissa1 & 1) == 0 && u.ieee.exponent != 0x7ff)
+ u.ieee.mantissa1 |= fetestexcept (FE_INEXACT) != 0;
+ feupdateenv (&env);
+ /* Result is a1 + u.d, scaled up. */
+ return (a1 + u.d) * 0x1p53;
+ }
+ else
+ {
+ v.d = a1 + u.d;
+ int j = fetestexcept (FE_INEXACT) != 0;
+ feupdateenv (&env);
+ /* Ensure the following computations are performed in default rounding
+ mode instead of just reusing the round to zero computation. */
+ asm volatile ("" : "=m" (u) : "m" (u));
+ /* If a1 + u.d is exact, the only rounding happens during
+ scaling down. */
+ if (j == 0)
+ return v.d * 0x1p-106;
+ /* If result rounded to zero is not subnormal, no double
+ rounding will occur. */
+ if (v.ieee.exponent > 106)
+ return (a1 + u.d) * 0x1p-106;
+ /* If v.d * 0x1p-106 with round to zero is a subnormal above
+ or equal to DBL_MIN / 2, then v.d * 0x1p-106 shifts mantissa
+ down just by 1 bit, which means v.ieee.mantissa1 |= j would
+ change the round bit, not sticky or guard bit.
+ v.d * 0x1p-106 never normalizes by shifting up,
+ so round bit plus sticky bit should be already enough
+ for proper rounding. */
+ if (v.ieee.exponent == 106)
+ {
+ /* v.ieee.mantissa1 & 2 is LSB bit of the result before rounding,
+ v.ieee.mantissa1 & 1 is the round bit and j is our sticky
+ bit. In round-to-nearest 001 rounds down like 00,
+ 011 rounds up, even though 01 rounds down (thus we need
+ to adjust), 101 rounds down like 10 and 111 rounds up
+ like 11. */
+ if ((v.ieee.mantissa1 & 3) == 1)
+ {
+ v.d *= 0x1p-106;
+ if (v.ieee.negative)
+ return v.d - 0x1p-1074 /* __DBL_DENORM_MIN__ */;
+ else
+ return v.d + 0x1p-1074 /* __DBL_DENORM_MIN__ */;
+ }
+ else
+ return v.d * 0x1p-106;
+ }
+ v.ieee.mantissa1 |= j;
+ return v.d * 0x1p-106;
+ }
}
#ifndef __fma
weak_alias (__fma, fma)