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Full Discussion: Strange value of the double type variable: -nan(0x8000000000000)
Top Forums Programming Strange value of the double type variable: -nan(0x8000000000000) Post 302903932 by 915086731 on Saturday 31st of May 2014 12:32:18 AM
Old 05-31-2014
Code:
tmp1 = (simtime - seg->time) / currdisk->rotatetime;
currdisk->currangle += tmp1;

The above code can also cause NaN in the later calling.
So I step into to the assembly.
tmp1 = (simtime - seg->time) / currdisk->rotatetime;
Code:
0x0808fdf4  <disk_buffer_sector_done+559>:  fldl   0x80b2208
0x0808fdfa  <disk_buffer_sector_done+565>:  mov    -0x38(%ebp),%eax
0x0808fdfd  <disk_buffer_sector_done+568>:  fldl   (%eax)

...Here, the content of %eax is 0x80bdfeb, which is the address of seg->time.
After the above "fldl (%eax) " executed, the content of register st0 is 0x8000000000000000, which represents NaN.
So the NaN is propagated to the following instructions. This is the key issue.
Code:
0x0808fdff  <disk_buffer_sector_done+570>:  fsubrp %st,%st(1)
0x0808fe01  <disk_buffer_sector_done+572>:  mov    0x8(%ebp),%eax
0x0808fe04  <disk_buffer_sector_done+575>:  fldl   0xc4(%eax)
0x0808fe0a  <disk_buffer_sector_done+581>:  fdivrp %st,%st(1)
0x0808fe0c  <disk_buffer_sector_done+583>:  fstpl  -0x28(%ebp)

 

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LEARN ABOUT MINIX

nan

NAN(3)                                                       Linux Programmer's Manual                                                      NAN(3)

NAME

       nan, nanf, nanl - return 'Not a Number'

SYNOPSIS

       #include <math.h>

       double nan(const char *tagp);
       float nanf(const char *tagp);
       long double nanl(const char *tagp);

       Link with -lm.

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       nan(), nanf(), nanl():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

DESCRIPTION

       These  functions  return  a  representation  (determined by tagp) of a quiet NaN.  If the implementation does not support quiet NaNs, these
       functions return zero.

       The call nan("char-sequence") is equivalent to:

           strtod("NAN(char-sequence)", NULL);

       Similarly, calls to nanf() and nanl() are equivalent to analogous calls to strtof(3) and strtold(3).

       The argument tagp is used in an unspecified manner.  On IEEE 754 systems, there are many representations of NaN, and tagp selects one.   On
       other systems it may do nothing.

VERSIONS

       These functions first appeared in glibc in version 2.1.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       +----------------------+---------------+----------------+
       |Interface             | Attribute     | Value          |
       +----------------------+---------------+----------------+
       |nan(), nanf(), nanl() | Thread safety | MT-Safe locale |
       +----------------------+---------------+----------------+
CONFORMING TO

       C99, POSIX.1-2001, POSIX.1-2008.  See also IEC 559 and the appendix with recommended functions in IEEE 754/IEEE 854.

SEE ALSO

       isnan(3), strtod(3), math_error(7)

COLOPHON

       This  page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

GNU                                                                 2016-03-15                                                              NAN(3)
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