Encoding:

POOL16B

001001

rd

rt

encoded

sa

0

6

3

3

3

1

Format: 

SLL16 rd, rt, decoded_sa

microMIPS

Shift Word Left Logical (16-bit instr size)

Purpose:

Shift Word Left Logical (16-bit instr size)

To left-shift a word by a fixed number of bits

Description: 

 GPR[rd] = GPR[rt] << decoded_sa

The contents of the low-order 32-bit word of GPR rt are shifted left, inserting zeros into the emptied bits; the word result is sign-extended and placed in GPR rd. The bit-shift amount is specified by decoding the encoded_sa field.

Table 5.15 lists the encoded values of the encoded_sa field and the actual bit shift amount values.

Table 5.15 Shift Amount Field Encoding

Encoded Input

(Hex)

Decoded Value

(Decimal)

0

8

1

1

2

2

3

3

4

4

5

5

6

6

7

7

Restrictions:

The 3-bit register fields can only specify GPRs $2-$7, $16, $17.

Operation: 

decoded_sa = DECODE(encoded_sa)
s = decoded_sa
temp = GPR[rt](31-s)..0 || 0s
GPR[rd] = sign_extend(temp)

Exceptions:

None

Programming Notes:

Unlike nearly all other word operations, the SLL input operand does not have to be a properly sign-extended word value to produce a valid sign-extended 32-bit result. The result word is always sign-extended into a 64-bit destination register; this instruction with a zero shift amount truncates a 64-bit value to 32 bits and sign-extends it.