Propeller Manual

SAR – Assembly Language Reference
SAR
Instruction: Shift value arithmetically right by specified number of bits.
SAR Value, 〈#〉 Bits
Result: Value is shifted arithmetically right by Bits.
•
Value (d-field) is the register to shift arithmetically right.
•
Bits (s-field) is a register or a 5-bit literal whose value is the number of bits to shift
arithmetically right.
Opcode Table:
–INSTR– ZCRI –CON– –DEST– –SRC– Z Result C Result Result Clocks
001110 001i 1111 ddddddddd sssssssss
Result = 0 D[0] Written 4
Concise Truth Table:
In Out
Destination Source Z C Effects Destination Z C
$FFFF_FF9C; -100 $0000_0001; 1 - -
wz wc
$FFFF_FFCE; -50 0 0
$FFFF_FF9C; -100 $0000_0002; 2 - -
wz wc
$FFFF_FFE7; -25 0 0
$FFFF_FF9C; -100 $0000_0003; 3 - -
wz wc
$FFFF_FFF3; -13 0 0
$FFFF_FFF3; -13 $0000_0001; 1 - -
wz wc
$FFFF_FFF9; -7 0 1
$FFFF_FFF9; -7 $0000_0001; 1 - -
wz wc
$FFFF_FFFC; -4 0 1
$FFFF_FFFC; -4 $0000_0001; 1 - -
wz wc
$FFFF_FFFE; -2 0 0
$0000_0006; 6 $0000_0001; 1 - -
wz wc
$0000_0003; 3 0 0
$0000_0006; 6 $0000_0002; 2 - -
wz wc
$0000_0001; 1 0 0
$0000_0006; 6 $0000_0003; 3 - -
wz wc
$0000_0000; 0 1 0
Explanation
SAR (Shift Arithmetic Right) shifts Value right by Bits places, extending the MSB along the
way. This has the effect of preserving the sign in a signed value, thus
SAR is a quick divide-
by-power-of-two for signed integer values.
If the
WZ effect is specified, the Z flag is set (1) if the resulting Value equals zero. If the WC
effect is specified, the C flag is set equal to Value’s original bit 0. The result is written to
Value unless the
NR effect is specified.
Page 346 · Propeller Manual v1.1