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Fix spurious undeflow for ldbl-128ibm erfl

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For values higher than 25.6283 erflc underflow, so adjust erfl
to return a constant value based argument sign.
This commit is contained in:
Adhemerval Zanella 2012-06-05 10:42:49 -03:00
parent 34ae0b3270
commit 6043738b36
2 changed files with 23 additions and 3 deletions
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5
ChangeLog
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@ -1,3 +1,8 @@
2012-06-05 Adhemerval Zanella <azanella@linux.vnet.ibm.com>
* sysdeps/ieee754/ldbl-128ibm/s_erfl.c: Fix spurious underflow for
values higher than 25.6283.
2012-06-04 Adhemerval Zanella <azanella@linux.vnet.ibm.com>
* sysdeps/ieee754/ldbl-128ibm/e_fmodl.c (__ieee754_fmodl): Fix

21
sysdeps/ieee754/ldbl-128ibm/s_erfl.c
View File

@ -72,6 +72,8 @@
* z=1/x^2
* The interval is partitioned into several segments
* of width 1/8 in 1/x.
* erf(x) = 1.0 - erfc(x) if x < 25.6283 else
* erf(x) = sign(x)*(1.0 - tiny)
*
* Note1:
* To compute exp(-x*x-0.5625+R/S), let s be a single
@ -85,6 +87,9 @@
* erfc(x) ~ ---------- * ( 1 + Poly(1/x^2) )
* x*sqrt(pi)
*
* Note3:
* For x higher than 25.6283, erf(x) underflows.
*
* 5. For inf > x >= 107
* erf(x) = sign(x) *(1 - tiny) (raise inexact)
* erfc(x) = tiny*tiny (raise underflow) if x > 0
@ -770,9 +775,19 @@ __erfl (long double x)
if (ix >= 0x3ff00000) /* |x| >= 1.0 */
{
y = __erfcl (x);
return (one - y);
/* return (one - __erfcl (x)); */
if (ix >= 0x4039A0DE)
{
/* __erfcl (x) underflows if x > 25.6283 */
if (sign)
return one-tiny;
else
return tiny-one;
}
else
{
y = __erfcl (x);
return (one - y);
}
}
u.parts32.w0 = ix;
a = u.value;