Representation of hexadecimal floating point

The assembler assembles a floating-point constant into its binary representation as follows: The specified number, multiplied by any exponents, is converted to the required two-part format. The value is translated into:

A fractional portion represented by hexadecimal digits and the sign indicator. The fraction is then entered into the leftmost part of the fraction field of the constant (after rounding).
An exponent portion represented by the excess-64 binary notation, which is then entered into the characteristic field of the constant.

The excess-64 binary notation is obtained by adding +64 to the value of the exponent (-64 - +63) to yield the characteristic (0 - 127).

Notes:

The L-type floating-point constant resembles two contiguous D-type constants. The sign of the second doubleword is assumed to be the same as the sign of the first.
The characteristic for the second doubleword is equal to the characteristic for the first minus 14 (the number of hexadecimal digits in the fractional portion of the first doubleword). No indication is given if the characteristic of the second doubleword is zero.

The L-type and LH-type floating-point constants are doubleword aligned. The LQ-type is quadword aligned. A DC 0LQ forces the alignment to a quadword boundary.
If scaling has been specified, hexadecimal zeros are added to the left of the normalized fraction (causing it to become unnormalized), and the exponent in the characteristic field is adjusted accordingly. (For further details on scaling, see Subfield 5: Modifier.)
The fraction is rounded according to the implied or explicit length of the constant. The resulting number does not differ from the exact value specified by more than one in the last place.
Note: You can control rounding by using the 'H' type extension and specifying the rounding mode.
Negative fractions are carried in true representation, not in the two's-complement form.
Duplication is applied after the constant has been assembled.
An implied length of 4 bytes is assumed for a short (E) constant and eight bytes for a long (D) constant. An implied length of 16 bytes is assumed for an extended (L) constant. The constant is aligned at the correct word (E) or doubleword (D and L) boundary if a length is not specified. However, any length up to and including eight bytes (E and D) or 16 bytes (L) can be specified by a length modifier. In this case, no boundary alignment occurs.
Signed zero values are correctly generated for type extensions H and B. Without a type extension, zero values of either sign are assembled with positive sign.

Any of the following statements can be used to specify 46.415 as a positive, fullword, floating-point constant; the last is a machine instruction statement with a literal operand. Each of the last two constants contains an exponent modifier.

         DC              E'46.415'
         DC              E'46415E-3'
         DC              E'+464.15E-1'
         DC              E'+.46415E+2'
         DC              EE2'.46415'
         AE              6,=EE2'.46415'

The following generates 3 doubleword floating-point constants.

FLOAT    DC              DE(+4)'+46,-3.729,+473'