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Re: [BZ #15522] strtod ("nan(N)") returning a sNaN in some cases


Hi!

Ping.

On Fri, 31 May 2013 09:00:00 +0200, I wrote:
> Ping.
> 
> On Thu, 23 May 2013 18:00:10 +0200, Thomas Schwinge <thomas@codesourcery.com> wrote:
> > BZ #15522:
> > | strtod ("nan(N)") (and likewise for the other float types) exhibits wrong
> > | behavior such that for architectures defining
> > | HIGH_ORDER_BIT_IS_SET_FOR_SNAN, a sNaN is returned for N = 0, and for
> > | other architectures a sNaN is returned for positive integral N != 0.
> > 
> > Use the ieee754_* unions' ieee_nan member for easily setting a NaN's
> > mantissa without touching the quiet/signaling bit (or anything else), and
> > only if that new mantissa is unequal to zero (denoting infinity) use it
> > to overwrite the generic NaN's mantissa (which has been pre-set before
> > invoking SET_MANTISSA).
> > 
> > Tested for several MIPS multilibs, x86, x86_64, PowerPC -m64 (but a
> > PowerPC maintainer please confirm the
> > sysdeps/ieee754/ldbl-128ibm/ieee754.h change; I copied the ieee member
> > and changed it as done for other ldbl-*/ieee754.h's long double
> > structures/unions).
> > 
> > 	* stdlib/strtof_l.c (SET_MANTISSA): Rewrite.
> > 	* stdlib/strtod_l.c (SET_MANTISSA): Likewise.
> > 	* sysdeps/ieee754/ldbl-64-128/strtold_l.c (SET_MANTISSA): Likewise.
> > 	* sysdeps/ieee754/ldbl-96/strtold_l.c (SET_MANTISSA): Likewise.
> > 	* sysdeps/ieee754/ldbl-128/strtold_l.c (SET_MANTISSA): Likewise.
> > 	* sysdeps/ieee754/ldbl-128ibm/strtold_l.c (SET_MANTISSA): Likewise.
> > 	* sysdeps/ieee754/ldbl-128ibm/ieee754.h (ibm_extended_long_double):
> > 	Add ieee_nan member.
> > 	* stdlib/tst-strtod6.c (test): New function, renamed from do_test.
> > 	(do_test): New function.
> > 
> > diff --git stdlib/strtod_l.c stdlib/strtod_l.c
> > index 47247b5..5ed5a35 100644
> > --- stdlib/strtod_l.c
> > +++ stdlib/strtod_l.c
> > @@ -42,11 +42,10 @@ extern unsigned long long int ____strtoull_l_internal (const char *, char **,
> >  # define SET_MANTISSA(flt, mant) \
> >    do { union ieee754_double u;						      \
> >         u.d = (flt);							      \
> > -       if ((mant & 0xfffffffffffffULL) == 0)				      \
> > -	 mant = 0x8000000000000ULL;					      \
> > -       u.ieee.mantissa0 = ((mant) >> 32) & 0xfffff;			      \
> > -       u.ieee.mantissa1 = (mant) & 0xffffffff;				      \
> > -       (flt) = u.d;							      \
> > +       u.ieee_nan.mantissa0 = (mant) >> 32;				      \
> > +       u.ieee_nan.mantissa1 = (mant);					      \
> > +       if ((u.ieee.mantissa0 | u.ieee.mantissa1) != 0)			      \
> > +	 (flt) = u.d;							      \
> >    } while (0)
> >  #endif
> >  /* End of configuration part.  */
> > diff --git stdlib/strtof_l.c stdlib/strtof_l.c
> > index 6fb44bd..c4c1c1f 100644
> > --- stdlib/strtof_l.c
> > +++ stdlib/strtof_l.c
> > @@ -37,10 +37,9 @@ extern unsigned long long int ____strtoull_l_internal (const char *, char **,
> >  #define SET_MANTISSA(flt, mant) \
> >    do { union ieee754_float u;						      \
> >         u.f = (flt);							      \
> > -       if ((mant & 0x7fffff) == 0)					      \
> > -	 mant = 0x400000;						      \
> > -       u.ieee.mantissa = (mant) & 0x7fffff;				      \
> > -       (flt) = u.f;							      \
> > +       u.ieee_nan.mantissa = (mant);					      \
> > +       if (u.ieee.mantissa != 0)					      \
> > +	 (flt) = u.f;							      \
> >    } while (0)
> >  
> >  #include "strtod_l.c"
> > diff --git stdlib/tst-strtod6.c stdlib/tst-strtod6.c
> > index 1d87266..15e79fd 100644
> > --- stdlib/tst-strtod6.c
> > +++ stdlib/tst-strtod6.c
> > @@ -4,12 +4,13 @@
> >  #include <string.h>
> >  
> >  static int
> > -do_test (void)
> > +test (const char str[])
> >  {
> > -  static const char str[] = "NaN(blabla)something";
> >    char *endp;
> >    int result = 0;
> >  
> > +  puts (str);
> > +
> >    double d = strtod (str, &endp);
> >    if (!isnan (d))
> >      {
> > @@ -64,5 +65,24 @@ do_test (void)
> >    return result;
> >  }
> >  
> > +static int
> > +do_test (void)
> > +{
> > +  int result = 0;
> > +
> > +  result |= test ("NaN(blabla)something");
> > +  result |= test ("NaN(1234)something");
> > +  /* UINT32_MAX.  */
> > +  result |= test ("NaN(4294967295)something");
> > +  /* UINT64_MAX.  */
> > +  result |= test ("NaN(18446744073709551615)something");
> > +  /* The case of zero is special in that "something" has to be done to make the
> > +     mantissa different from zero, which would mean infinity instead of
> > +     NaN.  */
> > +  result |= test ("NaN(0)something");
> > +
> > +  return result;
> > +}
> > +
> >  #define TEST_FUNCTION do_test ()
> >  #include "../test-skeleton.c"
> > diff --git sysdeps/ieee754/ldbl-128/strtold_l.c sysdeps/ieee754/ldbl-128/strtold_l.c
> > index 8e0bc03..d3a1d1e 100644
> > --- sysdeps/ieee754/ldbl-128/strtold_l.c
> > +++ sysdeps/ieee754/ldbl-128/strtold_l.c
> > @@ -34,11 +34,13 @@
> >  #define SET_MANTISSA(flt, mant) \
> >    do { union ieee854_long_double u;					      \
> >         u.d = (flt);							      \
> > -       u.ieee.mantissa0 = 0x8000;					      \
> > -       u.ieee.mantissa1 = 0;						      \
> > -       u.ieee.mantissa2 = ((mant) >> 32);	      			      \
> > -       u.ieee.mantissa3 = (mant) & 0xffffffff;				      \
> > -       (flt) = u.d;							      \
> > +       u.ieee_nan.mantissa0 = 0;					      \
> > +       u.ieee_nan.mantissa1 = 0;					      \
> > +       u.ieee_nan.mantissa2 = (mant) >> 32;				      \
> > +       u.ieee_nan.mantissa3 = (mant);					      \
> > +       if ((u.ieee.mantissa0 | u.ieee.mantissa1				      \
> > +	    | u.ieee.mantissa2 | u.ieee.mantissa3) != 0)		      \
> > +	 (flt) = u.d;							      \
> >    } while (0)
> >  
> >  #include <strtod_l.c>
> > diff --git sysdeps/ieee754/ldbl-128ibm/ieee754.h sysdeps/ieee754/ldbl-128ibm/ieee754.h
> > index e5644f5..9e94f53 100644
> > --- sysdeps/ieee754/ldbl-128ibm/ieee754.h
> > +++ sysdeps/ieee754/ldbl-128ibm/ieee754.h
> > @@ -199,6 +199,25 @@ union ibm_extended_long_double
> >  	unsigned int mantissa2:20;
> >  	unsigned int mantissa3:32;
> >        } ieee;
> > +
> > +    /* This format makes it easier to see if a NaN is a signalling NaN.  */
> > +    struct
> > +      { /* Big endian.  There is no other.  */
> > +
> > +	unsigned int negative:1;
> > +	unsigned int exponent:11;
> > +	unsigned int quiet_nan:1;
> > +	/* Together Mantissa0-3 comprise the mantissa.  */
> > +	unsigned int mantissa0:19;
> > +	unsigned int mantissa1:32;
> > +
> > +	unsigned int negative2:1;
> > +	unsigned int exponent2:11;
> > +	/* There is an implied 1 here?  */
> > +	/* Together these comprise the mantissa.  */
> > +	unsigned int mantissa2:20;
> > +	unsigned int mantissa3:32;
> > +      } ieee_nan;
> >     };
> >  
> >  #define IBM_EXTENDED_LONG_DOUBLE_BIAS 0x3ff /* Added to exponent.  */
> > diff --git sysdeps/ieee754/ldbl-128ibm/strtold_l.c sysdeps/ieee754/ldbl-128ibm/strtold_l.c
> > index 93415f0..04e3288 100644
> > --- sysdeps/ieee754/ldbl-128ibm/strtold_l.c
> > +++ sysdeps/ieee754/ldbl-128ibm/strtold_l.c
> > @@ -44,11 +44,10 @@ libc_hidden_proto (STRTOF)
> >  # define SET_MANTISSA(flt, mant) \
> >    do { union ibm_extended_long_double u;				      \
> >         u.d = (flt);							      \
> > -       if ((mant & 0xfffffffffffffULL) == 0)				      \
> > -	 mant = 0x8000000000000ULL;					      \
> > -       u.ieee.mantissa0 = ((mant) >> 32) & 0xfffff;			      \
> > -       u.ieee.mantissa1 = (mant) & 0xffffffff;				      \
> > -       (flt) = u.d;							      \
> > +       u.ieee_nan.mantissa0 = (mant) >> 32;				      \
> > +       u.ieee_nan.mantissa1 = (mant);					      \
> > +       if ((u.ieee.mantissa0 | u.ieee.mantissa1) != 0)			      \
> > +	 (flt) = u.d;							      \
> >    } while (0)
> >  
> >  #include <strtod_l.c>
> > diff --git sysdeps/ieee754/ldbl-64-128/strtold_l.c sysdeps/ieee754/ldbl-64-128/strtold_l.c
> > index 8182b2b..e9b33f2 100644
> > --- sysdeps/ieee754/ldbl-64-128/strtold_l.c
> > +++ sysdeps/ieee754/ldbl-64-128/strtold_l.c
> > @@ -44,11 +44,13 @@ libc_hidden_proto (STRTOF)
> >  #define SET_MANTISSA(flt, mant) \
> >    do { union ieee854_long_double u;					      \
> >         u.d = (flt);							      \
> > -       u.ieee.mantissa0 = 0x8000;					      \
> > -       u.ieee.mantissa1 = 0;						      \
> > -       u.ieee.mantissa2 = ((mant) >> 32);	      			      \
> > -       u.ieee.mantissa3 = (mant) & 0xffffffff;				      \
> > -       (flt) = u.d;							      \
> > +       u.ieee_nan.mantissa0 = 0;					      \
> > +       u.ieee_nan.mantissa1 = 0;					      \
> > +       u.ieee_nan.mantissa2 = (mant) >> 32;				      \
> > +       u.ieee_nan.mantissa3 = (mant);					      \
> > +       if ((u.ieee.mantissa0 | u.ieee.mantissa1				      \
> > +	    | u.ieee.mantissa2 | u.ieee.mantissa3) != 0)		      \
> > +	 (flt) = u.d;							      \
> >    } while (0)
> >  
> >  #include <strtod_l.c>
> > diff --git sysdeps/ieee754/ldbl-96/strtold_l.c sysdeps/ieee754/ldbl-96/strtold_l.c
> > index ded84f3..dccf98c 100644
> > --- sysdeps/ieee754/ldbl-96/strtold_l.c
> > +++ sysdeps/ieee754/ldbl-96/strtold_l.c
> > @@ -34,11 +34,10 @@
> >  #define SET_MANTISSA(flt, mant) \
> >    do { union ieee854_long_double u;					      \
> >         u.d = (flt);							      \
> > -       if ((mant & 0x7fffffffffffffffULL) == 0)				      \
> > -	 mant = 0x4000000000000000ULL;					      \
> > -       u.ieee.mantissa0 = (((mant) >> 32) & 0x7fffffff) | 0x80000000;	      \
> > -       u.ieee.mantissa1 = (mant) & 0xffffffff;				      \
> > -       (flt) = u.d;							      \
> > +       u.ieee_nan.mantissa0 = (mant) >> 32;				      \
> > +       u.ieee_nan.mantissa1 = (mant);					      \
> > +       if ((u.ieee.mantissa0 | u.ieee.mantissa1) != 0)			      \
> > +	 (flt) = u.d;							      \
> >    } while (0)
> >  
> >  #include <stdlib/strtod_l.c>
> > 
> > 
> > I used the following hack for manually verifying the expected bit
> > patterns for the resulting NaNs' mantissas; not proposing to commit.  ;-)
> > 
> > diff --git stdlib/tst-strtod6.c stdlib/tst-strtod6.c
> > index 15e79fd..05532b6 100644
> > --- stdlib/tst-strtod6.c
> > +++ stdlib/tst-strtod6.c
> > @@ -2,6 +2,7 @@
> >  #include <stdio.h>
> >  #include <stdlib.h>
> >  #include <string.h>
> > +#include <stdint.h>
> >  
> >  static int
> >  test (const char str[])
> > @@ -12,6 +13,9 @@ test (const char str[])
> >    puts (str);
> >  
> >    double d = strtod (str, &endp);
> > +  printf("%08x ", ((uint32_t *) &d)[0]);
> > +  printf("%08x ", ((uint32_t *) &d)[1]);
> > +  puts("");
> >    if (!isnan (d))
> >      {
> >        puts ("strtod did not return NAN");
> > @@ -29,6 +33,8 @@ test (const char str[])
> >      }
> >  
> >    float f = strtof (str, &endp);
> > +  printf("%08x ", ((uint32_t *) &f)[0]);
> > +  puts("");
> >    if (!isnanf (f))
> >      {
> >        puts ("strtof did not return NAN");
> > @@ -46,6 +52,11 @@ test (const char str[])
> >      }
> >  
> >    long double ld = strtold (str, &endp);
> > +  printf("%08x ", ((uint32_t *) &ld)[0]);
> > +  printf("%08x ", ((uint32_t *) &ld)[1]);
> > +  printf("%08x ", ((uint32_t *) &ld)[2]);
> > +  printf("%08x ", ((uint32_t *) &ld)[3]);
> > +  puts("");
> >    if (!isnan (ld))
> >      {
> >        puts ("strtold did not return NAN");


GrÃÃe,
 Thomas

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