#2 Incorrect arithmetic ops & addressing

[Carlos Rodriguez]

16 bit arithmetic operations are coded with 8 bit data
types, so results are completely incorrect.

Sign extension in JR and DJNZ is.... maybe not
incorrect, but coded in an excessively complicated way;
it should be enough to cast from 'byte' to 'char', and
then to 'int'.

Indexed addressing offsets are not correctly
calculated: addresses are 16 bit wide, UNSIGNED, and
offsets are 8 bit wide, SIGNED. As sign extension is
not being done in those cases, negative offsets are
incorrectly calculated.

Mmmm.... are you sure this library has ever been useful???

[Gabriel Gambetta]

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> Mmmm.... are you sure this library has ever been
useful???

Not exactly this code, but most if it comes from fairly solid
and working code. I'll check your reports, thanks!

[Philip Kendall]

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The original poster is basically correct; a significant
proportion of the opcodes are emulated incorrectly.

Attached is a small test program which runs the test suite
as supplied with Fuse
<http://sourceforge.net/projects/fuse-emulator/>; you'll
need the z80/tests directory from there.

Currently, 645 out of 1307 tests.