Howard M. Harte f57826c635 AltairZ80: i86: Don't clear segment override on REPE/REPNE ...

MASM generates REP CS:MOVSW as:

REP
CS:
MOVSW

The Seattle Computer Products 8086 assembler allows the segment override
as a discrete opcode.  This means that:

CS:
REP
MOVSW

is also possible, and in fact used in the SCP Monitor v1.6.

The i86 emulator was clearing the override flags when REPE/REPNE,
is encountered, which causes the segment override to be lost.
Verifying the behavior of a real 80286 processor in an IBM PC/AT
(5170) using MS-DOS 6.22 DEBUG shows that both instruction sequences
yield the desired segment override.

2022-11-05 19:55:40 -07:00

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