IBM Floating Point Architecture - Double-precision 64-bit

Double-precision 64-bit

Double-precision is the same except that the mantissa (fraction) field is wider and the double-precision number is stored in a double word (8 bytes):

1 7 56 bits +-+-----------+----------------------------------------------------+ |S| Exp | Fraction | +-+-----------+----------------------------------------------------+ 63 62 56 55 0

Note that the exponent range for this format is only about a quarter as large as the corresponding IEEE binary format.

14 hexadecimal digits of precision is roughly equivalent to 15 decimal digits. A conversion of double precision hexadecimal float to decimal string would require at least 18 significant digits in order to convert back to the same hexadecimal float value.