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collapseos/blk/299
Virgil Dupras d041b91846 Optimize chkPS
Use EXX instead of the stack for HL protection and remove all
spurious uses of chkPS,

I wanted to inline chkPS in next because of its "tight loop" status,
but for reasons I don't understand, doing so breaks Collapse OS.
Later...
2020-05-22 23:12:03 -04:00

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PC ORG @ 0x1e + ! ( chkPS )
( Note that you only need to call this in words that push
back to PSP. If they don't, calling chkPS is redundant with
check in next )
EXX,
( We have the return address for this very call on the stack
and protected registers. 2 - is to compensate that. )
HL PS_ADDR 2 - LDddnn,
SP SUBHLss,
EXX,
CNC RETcc, ( PS_ADDR >= SP? good )
JR, L2 BWR ( abortUnderflow-B298 )