@@ -7868,6 +7868,11 @@ static const struct test_f_f_data logb_test_data[] =
TEST_f_f (logb, 0x1p-16400L, -16400, NO_INEXACT_EXCEPTION),
TEST_f_f (logb, 0x.00000000001p-16382L, -16426, NO_INEXACT_EXCEPTION),
#endif
+
+#if defined TEST_LDOUBLE && LDBL_MANT_DIG >= 57
+ TEST_f_f (logb, 0x1.ffffffffffffffp1L, 1, NO_INEXACT_EXCEPTION),
+ TEST_f_f (logb, -0x1.ffffffffffffffp1L, 1, NO_INEXACT_EXCEPTION),
+#endif
};
static void
@@ -26,11 +26,12 @@
long double
__logbl (long double x)
{
- int64_t hx, rhx;
- double xhi;
+ int64_t hx, hxs, rhx;
+ double xhi, xlo;
- xhi = ldbl_high (x);
+ ldbl_unpack (x, &xhi, &xlo);
EXTRACT_WORDS64 (hx, xhi);
+ hxs = hx;
hx &= 0x7fffffffffffffffLL; /* high |x| */
if (hx == 0)
return -1.0 / fabs (x);
@@ -42,6 +43,16 @@ __logbl (long double x)
though it were normalized. */
rhx -= __builtin_clzll (hx) - 12;
}
+ else if ((hx & 0x000fffffffffffffLL) == 0)
+ {
+ /* If the high part is a power of 2, and the low part is nonzero
+ with the opposite sign, the low part affects the
+ exponent. */
+ int64_t lx;
+ EXTRACT_WORDS64 (lx, xlo);
+ if ((hxs ^ lx) < 0 && (lx & 0x7fffffffffffffffLL) != 0)
+ rhx--;
+ }
return (long double) (rhx - 1023);
}
#ifndef __logbl