Propeller Manual

3: Assembly Language Reference – SUBS
SUBS
Instruction: Subtract two signed values.
SUBS SValue1, 〈#〉 SValue2
Result: Difference of signed SValue1 and signed SValue2 is stored in SValue1.
•
SValue1 (d-field) is the register containing the value to subtract SValue2 from, and is
the destination in which to write the result.
•
SValue2 (s-field) is a register or a 9-bit literal whose value is subtracted from SValue1.
Opcode Table:
–INSTR– ZCRI –CON– –DEST– –SRC– Z Result C Result Result Clocks
110101 001i 1111 ddddddddd sssssssss
D - S = 0 Signed Overflow Written 4
Concise Truth Table:
In Out
Destination Source Z C Effects Destination Z C
$0000_0001; 1 $0000_0001; 1 - -
wz wc
$0000_0000; 0 1 0
$0000_0001; 1 $0000_0002; 2 - -
wz wc
$FFFF_FFFF; -1 0 0
$FFFF_FFFF; -1 $FFFF_FFFF; -1 - -
wz wc
$0000_0000; 0 1 0
$FFFF_FFFF; -1 $FFFF_FFFE; -2 - -
wz wc
$0000_0001; 1 0 0
$8000_0001; -2,147,483,647 $0000_0001; 1 - -
wz wc
$8000_0000; -2,147,483,648 0 0
$8000_0001; -2,147,483,647 $0000_0002; 2 - -
wz wc
$7FFF_FFFF; 2,147,483,647 0 1
$7FFF_FFFE; 2,147,483,646 $FFFF_FFFF; -1 - -
wz wc
$7FFF_FFFF; 2,147,483,647 0 0
$7FFF_FFFE; 2,147,483,646 $FFFF_FFFE; -2 - -
wz wc
$8000_0000; -2,147,483,648 0 1
Explanation
SUBS subtracts the signed SValue2 from the signed SValue1 and stores the result into the
SValue1 register.
If the
WZ effect is specified, the Z flag is set (1) if SValue1 − SValue2 equals zero. If the WC
effect is specified, the C flag is set (1) if the subtraction resulted in a signed overflow. The
result is written to SValue1 unless the
NR effect is specified.
To subtract signed, multi-long values, use
SUB, possibly SUBX, and finally SUBSX. See SUBSX
on page 352 for more information.
Propeller Manual v1.1 · Page 351