Greg Ewing wrote:
Lenard Lindstrom wrote:
The direction of the copy is controlled by a register flag... The
flag was set by the SDL copy code, but not cleared afterwards.
Blarg. Modes are a bad thing in machine languages
as well as user interfaces!
Hi Greg,
Yes, I wondered why a flag was used instead of distinct reverse copy
instructions. Just as a "movs" instruction is transformed into a string
copy by a single byte prefix code "rep", the operation could be reversed
with an additional prefix. Maybe Intel thought copy code could be reused
for both forwards an backwards copies. Or they wanted to keep the byte
count down. But since the data pointers have to be set up specifically
for copy direction it probably doesn't make much of a difference.
--
Lenard Lindstrom
<[EMAIL PROTECTED]>