Developer's Topics
Chapter 1, Floating point operations

Extended-precision

Extended-precision

Extended-precision floating point numbers have the following format on the Intel386(TM) microprocessor:

   79    78    64   63           0
|-----|----------|----------------|
| SIGN|  EXPONENT|  FRACTION      |
 ----------------------------------
                    ^
                    binary point
For extended precision, bit 63 is always a 1, and the decimal point comes after this bit. The other formats have an implicit bit 1 before the fraction, as explained in ``Normalized numbers''.
 ---------------------------------------------------------------------
 Field        Position     Full name
 ---------------------------------------------------------------------
 sign         79           sign bit (0==positive, 1==negative)
 exponent     78-64        exponent (biased by 16,383)
 fraction     63-0         fraction (bit 63=1, followed by the
                           decimal point.  Bits 62-0 are the fraction.