Propeller Manual

3: Assembly Language Reference – SUB
SUB
Instruction: Subtract two unsigned values.
SUB Value1, 〈#〉 Value2
Result: Difference of unsigned Value1 and unsigned Value2 is stored in Value1.
•
Value1 (d-field) is the register containing the value to subtract Value2 from, and is the
destination in which to write the result.
•
Value2 (s-field) is a register or a 9-bit literal whose value is subtracted from Value1.
Opcode Table:
–INSTR– ZCRI –CON– –DEST– –SRC– Z Result C Result Result Clocks
100001 001i 1111 ddddddddd sssssssss
D - S = 0 Unsigned Borrow Written 4
Concise Truth Table:
In Out
Destination
1
Source Z C Effects Destination Z C
$0000_0002; 2 $0000_0001; 1 - -
wz wc
$0000_0001; 1 0 0
$0000_0002; 2 $0000_0002; 2 - -
wz wc
$0000_0000; 0 1 0
$0000_0002; 2 $0000_0003; 3 - -
wz wc
$FFFF_FFFF; 4,294,967,295 0 1
1
Both Source and Destination are treated as unsigned values.
Explanation
SUB subtracts the unsigned Value2 from the unsigned Value1 and stores the result into the
Value1 register.
If the
WZ effect is specified, the Z flag is set (1) if Value1 − Value2 equals zero. If the WC
effect is specified, the C flag is set (1) if the subtraction resulted in an unsigned borrow (32-
bit overflow). The result is written to Value1 unless the
NR effect is specified.
To subtract unsigned, multi-long values, use
SUB followed by SUBX. See SUBX on page 354 for
more information.
Propeller Manual v1.1 · Page 349