Propeller Manual

CMP – Assembly Language Reference
CMP
Instruction: Compare two unsigned values.
CMP Value1, 〈#〉 Value2
Result: Optionally, equality and greater/lesser status is written to the Z and C flags.
•
Value1 (d-field) is the register containing the value to compare with that of Value2.
•
Value2 (s-field) is a register or a 9-bit literal whose value is compared with Value1.
Opcode Table:
–INSTR– ZCRI –CON– –DEST– –SRC– Z Result C Result Result Clocks
100001 000i 1111 ddddddddd sssssssss
D = S Unsigned (D < S) Not Written 4
Concise Truth Table:
In Out
Destination
1
Source
1
Z C Effects Destination
2
Z C
$0000_0003; 3 $0000_0002; 2 - -
wr wz wc
$0000_0001; 1 0 0
$0000_0003; 3 $0000_0003; 3 - -
wr wz wc
$0000_0000; 0 1 0
$0000_0003; 3 $0000_0004; 4 - -
wr wz wc
$FFFF_FFFF; -1
3
0 1
$8000_0000; 2,147,483,648 $7FFF_FFFF; 2,147,483,647 - -
wr wz wc
$0000_0001; 1 0
0
4
$7FFF_FFFF; 2,147,483,647 $8000_0000; 2,147,483,648 - -
wr wz wc
$FFFF_FFFF; -1
3
0
1
4
$FFFF_FFFE; 4,294,967,294 $FFFF_FFFF; 4,294,967,295 - -
wr wz wc
$FFFF_FFFF; -1
3
0 1
$FFFF_FFFE; 4,294,967,294 $FFFF_FFFE; 4,294,967,294 - -
wr wz wc
$0000_0000; 0 1 0
$FFFF_FFFE; 4,294,967,294 $FFFF_FFFD; 4,294,967,293 - -
wr wz wc
$0000_0001; 1 0 0
1
Both Source and Destination are treated as unsigned values.
2
Destination is not written unless the WR effect is given.
3
Destination Out (written Destination) may be thought of as either unsigned or signed; it is shown here as signed for demonstration
purposes only.
4
The C flag result of CMP (Compare Unsigned) may differ from CMPS (Compare Signed) where the “interpreted sign” of Source and
Destination are opposite. The first example in the second group, above, shows that CMP clears C because unsigned $8000_0000
(2,147,483,648) is not
less than unsigned $7FFF_FFFF (2,147,483,647). CMPS, however, would have set C because signed
$8000_0000 (-2,147,483,648) is
less than signed $7FFF_FFFF (2,147,483,647). The second example is the complementary case
where the Source and Destination values are switched.
Explanation
CMP (Compare Unsigned) compares the unsigned values of Value1 and Value2. The Z and C
flags, if written, indicate the relative equal, and greater or lesser relationship between the two.
Page 272 · Propeller Manual v1.1