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sim65: changes constant of the unstable "ANE" instruction to comply with 65x02 test suite.

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ANE (0x8b) is an unstable illegal opcode that depends on a "constant" value that isn't
really constant. It varies between machines, with temperature, and so on. Original sim65
behavior was to use the constant value 0xEF. To get the behavior in line with the 65x02
testsuite, we now use the value 0xEE instead, which is also a reasonable choice that can
be observed in practice.
This commit is contained in:
Sidney Cadot
2024-12-19 22:58:42 +01:00
parent c52d7b27e6
commit b14f883e73
1 changed files with 7 additions and 1 deletions
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8
src/sim65/6502.c
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@@ -969,8 +969,14 @@ static unsigned HaveIRQRequest;
} while (0);
/* ANE */
/* An "unstable" illegal opcode that depends on a "constant" value that isn't
* really constant. It varies between machines, with temperature, and so on.
* Original sim65 behavior was to use the constant 0xEF here. To get behavior
* in line with the 65x02 testsuite, we now use the value 0xEE instead,
* which is also a reasonable choice that can be observed in practice.
*/
#define ANE(Val) \
Val = (Regs.AC | 0xEF) & Regs.XR & Val; \
Val = (Regs.AC | 0xEE) & Regs.XR & Val; \
Regs.AC = Val; \
TEST_SF (Val); \
TEST_ZF (Val)