EXT: M68K instruction reference

extSign-extend 
Sign-extends a data register’s low byte to word or its low word to long.
Sizes .w .l, .w by default
Used in Bytes, words and longsM68K assembly
trap #15 and its tasksM68K assembly
Flappy ASMM68K assembly
Numbers and sizesAssembly basics
 
XNZVC –●●00
● depends on the result
0 always 0
– not changed
Forms  ext   
Operands Dn A data register, d0 to d7. More
ext.w, the default, copies the byte’s sign bit into bits 8 through 15 and leaves the upper word unchanged. ext.l copies the word’s sign bit into bits 16 through 31. The newly filled bits are 1 for a negative input and 0 for a nonnegative input.
 * --- Byte to word: sign-extends byte in low word ---
move.l #$0000007F, d0
ext.w d0 ; d0 = $0000007F (positive, no change)

move.l #$000000FF, d1
ext.w d1 ; d1 = $0000FFFF (-1 sign-extended)

* --- Word to long: sign-extends word ---
move.l #$00008000, d2
ext.l d2 ; d2 = $FFFF8000