Re: strtod ("nan") returns negative NaN

[Masamichi Hosoda <trueroad at trueroad dot jp>]

[...]
> By the way, here are the results of the test prints from an embedded
> 64-bit ARM:
> 
> strtof ("nan", NULL) = 0.000000
> strtof ("-nan", NULL) = 0.000000
> strtod ("nan", NULL) = nan
> strtod ("-nan", NULL) = nan
> strtold ("nan", NULL) = inf
> strtold ("-nan", NULL) =
> 2315841784746322880031071374419981810209660594968745666
> 57923565917084799991808.000000

If I understand correctly, qNaN definition for 64-bit ARM is wrong
like x86_64 and i386 definition was wrong.

The following code can generate the correct definition.

```
/* gcc arch-nans.c */

#include <inttypes.h>
#include <math.h>
#include <stdio.h>
#include <stdint.h>

int main (void)
{
  union
  {
    float f;
    uint32_t u;
  } fb;

  union
  {
    double d;
    uint32_t u[2];
  } db;

  union
  {
    long double ld;
    uint32_t u[4];
    uint16_t us[5];
  } ldb;

  fb.u = 0;
  fb.f = nanf ("");
  printf ("#define f_QNAN 0x%"PRIx32"\n", fb.u);

  db.u[0] = 0;
  db.u[1] = 0;
  db.d = nan ("");
  printf ("#define d_QNAN0 0x%"PRIx32"\n"
	  "#define d_QNAN1  0x%"PRIx32"\n", db.u[0], db.u[1]);

  ldb.u[0] = 0;
  ldb.u[1] = 0;
  ldb.u[2] = 0;
  ldb.u[3] = 0;
  ldb.ld = nanl ("");
  printf ("#define ld_QNAN0 0x%"PRIx32"\n"
	  "#define ld_QNAN1 0x%"PRIx32"\n"
	  "#define ld_QNAN2 0x%"PRIx32"\n"
	  "#define ld_QNAN2 0x%"PRIx32"\n",
	  ldb.u[0], ldb.u[1], ldb.u[2], ldb.u[3]);
  printf ("#define ldus_QNAN0 0x%"PRIx16"\n"
	  "#define ldus_QNAN1 0x%"PRIx16"\n"
	  "#define ldus_QNAN2 0x%"PRIx16"\n"
	  "#define ldus_QNAN3 0x%"PRIx16"\n"
	  "#define ldus_QNAN4 0x%"PRIx16"\n",
	  ldb.us[0], ldb.us[1], ldb.us[2], ldb.us[3], ldb.us[4]);
}
```

The result on Cygwin 64 bit (x86_64) and 32 bit (i386):
```
#define f_QNAN 0x7fc00000
#define d_QNAN0 0x0
#define d_QNAN1  0x7ff80000
#define ld_QNAN0 0x0
#define ld_QNAN1 0xc0000000
#define ld_QNAN2 0x7fff
#define ld_QNAN2 0x0
#define ldus_QNAN0 0x0
#define ldus_QNAN1 0x0
#define ldus_QNAN2 0x0
#define ldus_QNAN3 0xc000
#define ldus_QNAN4 0x7fff
```

My patch
0001-Fix-strtod-nan-returns-negative-NaN.patch
v2-0001-Fix-strtod-nan-returns-negative-NaN.patch
uses the generated definition.