84PCE:Syscalls:021D7C

Synopsis

Hypothesized Official Name: SignExtendDE_broken

Syscall Address: 021D7Ch

This is supposed to extend the signed 16-bit DE value to be 24-bit signed.

However, due to what looks like a copy-paste error by TI, this routine is pretty much useless.

It looks like they tried to use code from SignExtendBC, and forgot to change a byte.

Here is what this routine calls, if you can find a particular use for it, go for it.

SignExtendDE_broken:
 push af
  xor a
  ld (0D02AD7h), de
  bit 7, b                ; This should be d, not b
  jr z, +_
  dec a
_:
  ld (0D02AD9h), a
  ld de, (0D02AD7h)
 pop af
 ret