Difference between revisions of "84PCE:Syscalls:021D7C"

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(Synopsis)
(Synopsis)
Line 19: Line 19:
 
   ld (0D02AD7h), de
 
   ld (0D02AD7h), de
 
   bit 7, b                ; This should be d, not b
 
   bit 7, b                ; This should be d, not b
   jr z, _+
+
   jr z, +_
 
   dec a
 
   dec a
_+:
+
_:
 
   ld (0D02AD9h), a
 
   ld (0D02AD9h), a
 
   ld de, (0D02AD7h)
 
   ld de, (0D02AD7h)
 
  pop af
 
  pop af
 
  ret </nowiki>
 
  ret </nowiki>

Revision as of 14:02, 1 September 2015

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