4.8.1 Load F_floating

Format:

LDF

Fa.wf,disp.ab(Rb.ab)

!Memory format

Operation:

va {Rbv + SEXT(disp)}

CASE

big_endian_data: va’ va XOR 1002

little_endian_data: va’ va

ENDCASE

Fa (va’)<15> MAP_F((va’)<14:7>) (va’)<6:0> (va’)<31:16> 0<28:0>

Exceptions:

Access Violation

Fault on Read

Alignment

Translation Not Valid

Instruction mnemonics:

LDF

Load F_floating

Qualifiers:

None

Description:

LDF fetches an F_floating datum from memory and writes it to register Fa. If the data is not naturally aligned, an alignment exception is generated.

The MAP_F function causes the 8-bit memory-format exponent to be expanded to an 11-bit register-format exponent according to Table 2–1.

The virtual address is computed by adding register Rb to the sign-extended 16-bit displace- ment. For a big-endian longword access, va<2> (bit 2 of the virtual address) is inverted, and any memory management fault is reported for va (not va). The source operand is fetched from memory and the bytes are reordered to conform to the F_floating register format. The result is then zero-extended in the low-order longword and written to register Fa.

Instruction Descriptions 4–91

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Compaq ECQD2KCTE manual Load Ffloating, Format