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(libc.info)IEEE Floating Point

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IEEE Floating Point
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   Here is an example showing how the floating type measurements come
out for the most common floating point representation, specified by the
`IEEE Standard for Binary Floating Point Arithmetic (ANSI/IEEE Std
754-1985)'.  Nearly all computers designed since the 1980s use this
format.

   The IEEE single-precision float representation uses a base of 2.
There is a sign bit, a mantissa with 23 bits plus one hidden bit (so
the total precision is 24 base-2 digits), and an 8-bit exponent that
can represent values in the range -125 to 128, inclusive.

   So, for an implementation that uses this representation for the
`float' data type, appropriate values for the corresponding parameters
are:

     FLT_RADIX                             2
     FLT_MANT_DIG                         24
     FLT_DIG                               6
     FLT_MIN_EXP                        -125
     FLT_MIN_10_EXP                      -37
     FLT_MAX_EXP                         128
     FLT_MAX_10_EXP                      +38
     FLT_MIN                 1.17549435E-38F
     FLT_MAX                 3.40282347E+38F
     FLT_EPSILON             1.19209290E-07F

   Here are the values for the `double' data type:

     DBL_MANT_DIG                         53
     DBL_DIG                              15
     DBL_MIN_EXP                       -1021
     DBL_MIN_10_EXP                     -307
     DBL_MAX_EXP                        1024
     DBL_MAX_10_EXP                      308
     DBL_MAX         1.7976931348623157E+308
     DBL_MIN         2.2250738585072014E-308
     DBL_EPSILON     2.2204460492503131E-016