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strtod: Convert 64 bit double to 64 bit int during computation

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The gdtoa implementation uses the type long, defined as Long, in lots
of code.  For historical reason newlib defines Long as int32_t instead.

This works fine, as long as floating point exceptions are not enabled.
The conversion to 32 bit int can lead to a FE_INVALID situation.

Example:

  const char *str = "121645100408832000.0";
  char *ptr;

  feenableexcept (FE_INVALID);
  strtod (str, &ptr);

This leads to the following situation in strtod

  double aadj;
  Long L;

  [...]
  L = (Long)aadj;

For instance, on x86_64 the code here is

  cvttsd2si %xmm0,%eax

At this point, aadj is 2529648000.0 in our example.  The conversion to
32 bit %eax results in a negative int value, thus the conversion is
invalid.  With feenableexcept (FE_INVALID), a SIGFPE is raised.

Fix this by always using 64 bit ints here if double is not a 32 bit type
to avoid this type of FP exceptions.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen 2018-04-09 11:31:04 +02:00
parent 1ee6654e50
commit 27652b608d
1 changed files with 9 additions and 0 deletions
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9
newlib/libc/stdlib/strtod.c
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@ -1186,7 +1186,16 @@ _strtod_l (struct _reent *ptr, const char *__restrict s00, char **__restrict se,
#endif
if (y == z) {
/* Can we stop now? */
#ifndef _DOUBLE_IS_32BITS
/* If FE_INVALID floating point exceptions are
enabled, a conversion to a 32 bit value is
dangerous. A positive double value can result
in a negative 32 bit int, thus raising SIGFPE.
To avoid this, always convert into 64 bit here. */
__int64_t L = (__int64_t)aadj;
#else
L = (Long)aadj;
#endif
aadj -= L;
/* The tolerances below are conservative. */
if (dsign || dword1(rv) || dword0(rv) & Bndry_mask) {