🚀 go-pugleaf

In article <AGLEW.90Feb19195316@dwarfs.csg.uiuc.edu> aglew@dwarfs.csg.uiuc.edu (Andy Glew) writes:
| A few days ago there was a discussion about instructions useful in
| BITblt and friends - instructions for merging bitfields from two
| words, etc.  It was observed that these instructions frequently
| require 3 input operands, as well as a destination - making them
| awkward to fit into conventional RISCish 3 operand (2 input, 1 output)
| instruction formats, let alone the older 2 operand formats.  Implicit
| operands and/or destructive use of an operand must be assumed.
|
| (2) Another four input operand operation:
|     Concatenate two registers and shift, placing result in a register.
|     Possibly useful for assembling data that overlap word boundaries,
|     circular shifts, etc.

This is the Am29000's EXTRACT instruction.  We use a "residual
control" register to hold the shift amount, since that value is
changed less often than the data to be shifted.



	-- Tim Olson
	Advanced Micro Devices
	(tim@amd.com)