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Issue #7632: Fix a bug in dtoa.c that could lead to incorrectly-rounded results.

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This commit is contained in:
Mark Dickinson 2010-01-12 22:55:51 +00:00
parent 8efef5ce9f
commit 5ff4f279e6
3 changed files with 126 additions and 3 deletions
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24
Python/dtoa.c
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@ -1130,6 +1130,26 @@ quorem(Bigint *b, Bigint *S)
return q;
}
/* version of ulp(x) that takes bc.scale into account.
Assuming that x is finite and nonzero, and x / 2^bc.scale is exactly
representable as a double, sulp(x) is equivalent to 2^bc.scale * ulp(x /
2^bc.scale). */
static double
sulp(U *x, BCinfo *bc)
{
U u;
if (bc->scale && 2*P + 1 - ((word0(x) & Exp_mask) >> Exp_shift) > 0) {
/* rv/2^bc->scale is subnormal */
word0(&u) = (P+2)*Exp_msk1;
word1(&u) = 0;
return u.d;
}
else
return ulp(x);
}
/* return 0 on success, -1 on failure */
@ -1289,12 +1309,12 @@ bigcomp(U *rv, const char *s0, BCinfo *bc)
else if (dd < 0) {
if (!dsign) /* does not happen for round-near */
retlow1:
dval(rv) -= ulp(rv);
dval(rv) -= sulp(rv, bc);
}
else if (dd > 0) {
if (dsign) {
rethi1:
dval(rv) += ulp(rv);
dval(rv) += sulp(rv, bc);
}
}
else {