summaryrefslogtreecommitdiff
path: root/sysdeps/ieee754/ldbl-128ibm/e_powl.c
diff options
context:
space:
mode:
authorJoseph Myers <joseph@codesourcery.com>2016-02-19 01:07:40 +0000
committerJoseph Myers <joseph@codesourcery.com>2016-02-19 01:07:40 +0000
commitc091488e5172025eb4e96fcc1141edb89dbc9afd (patch)
tree5081dc911a41c3bfe40e50311b3e8072eca3fe02 /sysdeps/ieee754/ldbl-128ibm/e_powl.c
parent9120a57f4819965fa976d5de3b1d27b284319ed1 (diff)
downloadglibc-c091488e5172025eb4e96fcc1141edb89dbc9afd.tar.gz
Fix ldbl-128ibm powl overflow handling (bug 19674).
The ldbl-128ibm implementation of powl has some problems in the case of overflow or underflow, which are mainly visible in non-default rounding modes. * When overflow or underflow is detected early, the correct sign of an overflowing or underflowing result is not allowed for. This is mostly hidden in the default rounding mode by the errno-setting wrappers recomputing the result (except in non-default error-handling modes such as -lieee), but visible in other rounding modes where a result that is not zero or infinity causes the wrappers not to do the recomputation. * The final scaling is done before the sign is incorporated in the result, but should be done afterwards for correct overflowing and underflowing results in directed rounding modes. This patch fixes those problems. Tested for powerpc. [BZ #19674] * sysdeps/ieee754/ldbl-128ibm/e_powl.c (__ieee754_powl): Include sign in overflowing and underflowing results when overflow or underflow is detected early. Include sign in result before rather than after scaling.
Diffstat (limited to 'sysdeps/ieee754/ldbl-128ibm/e_powl.c')
-rw-r--r--sysdeps/ieee754/ldbl-128ibm/e_powl.c34
1 files changed, 17 insertions, 17 deletions
diff --git a/sysdeps/ieee754/ldbl-128ibm/e_powl.c b/sysdeps/ieee754/ldbl-128ibm/e_powl.c
index 90340e890e..861b44ac8b 100644
--- a/sysdeps/ieee754/ldbl-128ibm/e_powl.c
+++ b/sysdeps/ieee754/ldbl-128ibm/e_powl.c
@@ -148,7 +148,7 @@ long double
__ieee754_powl (long double x, long double y)
{
long double z, ax, z_h, z_l, p_h, p_l;
- long double y1, t1, t2, r, s, t, u, v, w;
+ long double y1, t1, t2, r, s, sgn, t, u, v, w;
long double s2, s_h, s_l, t_h, t_l, ay;
int32_t i, j, k, yisint, n;
uint32_t ix, iy;
@@ -263,6 +263,11 @@ __ieee754_powl (long double x, long double y)
if (((((u_int32_t) hx >> 31) - 1) | yisint) == 0)
return (x - x) / (x - x);
+ /* sgn (sign of result -ve**odd) = -1 else = 1 */
+ sgn = one;
+ if (((((u_int32_t) hx >> 31) - 1) | (yisint - 1)) == 0)
+ sgn = -one; /* (-ve)**(odd int) */
+
/* |y| is huge.
2^-16495 = 1/2 of smallest representable value.
If (1 - 1/131072)^y underflows, y > 1.4986e9 */
@@ -272,15 +277,15 @@ __ieee754_powl (long double x, long double y)
if (iy > 0x47d654b0)
{
if (ix <= 0x3fefffff)
- return (hy < 0) ? huge * huge : tiny * tiny;
+ return (hy < 0) ? sgn * huge * huge : sgn * tiny * tiny;
if (ix >= 0x3ff00000)
- return (hy > 0) ? huge * huge : tiny * tiny;
+ return (hy > 0) ? sgn * huge * huge : sgn * tiny * tiny;
}
/* over/underflow if x is not close to one */
if (ix < 0x3fefffff)
- return (hy < 0) ? huge * huge : tiny * tiny;
+ return (hy < 0) ? sgn * huge * huge : sgn * tiny * tiny;
if (ix > 0x3ff00000)
- return (hy > 0) ? huge * huge : tiny * tiny;
+ return (hy > 0) ? sgn * huge * huge : sgn * tiny * tiny;
}
ay = y > 0 ? y : -y;
@@ -351,11 +356,6 @@ __ieee754_powl (long double x, long double y)
t1 = ldbl_high (t1);
t2 = z_l - (((t1 - t) - dp_h[k]) - z_h);
- /* s (sign of result -ve**odd) = -1 else = 1 */
- s = one;
- if (((((u_int32_t) hx >> 31) - 1) | (yisint - 1)) == 0)
- s = -one; /* (-ve)**(odd int) */
-
/* split up y into y1+y2 and compute (y1+y2)*(t1+t2) */
y1 = ldbl_high (y);
p_l = (y - y1) * t1 + y * t2;
@@ -367,22 +367,22 @@ __ieee754_powl (long double x, long double y)
{
/* if z > 16384 */
if (((j - 0x40d00000) | lj) != 0)
- return s * huge * huge; /* overflow */
+ return sgn * huge * huge; /* overflow */
else
{
if (p_l + ovt > z - p_h)
- return s * huge * huge; /* overflow */
+ return sgn * huge * huge; /* overflow */
}
}
else if ((j & 0x7fffffff) >= 0x40d01b90) /* z <= -16495 */
{
/* z < -16495 */
if (((j - 0xc0d01bc0) | lj) != 0)
- return s * tiny * tiny; /* underflow */
+ return sgn * tiny * tiny; /* underflow */
else
{
if (p_l <= z - p_h)
- return s * tiny * tiny; /* underflow */
+ return sgn * tiny * tiny; /* underflow */
}
}
/* compute 2**(p_h+p_l) */
@@ -408,8 +408,8 @@ __ieee754_powl (long double x, long double y)
t1 = z - t * u / v;
r = (z * t1) / (t1 - two) - (w + z * w);
z = one - (r - z);
- z = __scalbnl (z, n);
- math_check_force_underflow_nonneg (z);
- return s * z;
+ z = __scalbnl (sgn * z, n);
+ math_check_force_underflow (z);
+ return z;
}
strong_alias (__ieee754_powl, __powl_finite)