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


Hi!

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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