Encoding:

POOL32A

000000

rt

rs

bp

BALIGN

00100010

POOL32Axf

111100

6

5

5

2

8

6

SPECIAL3

011111

rs

rt

0

bp

BALIGN

10000

APPEND

110001

6

5

5

3

2

5

6

Format: 

BALIGN rt, rs, bp

microMIPSDSP-R2

Byte Align Contents from Two Registers

Purpose:

Byte Align Contents from Two Registers

Create a word result by combining a specified number of bytes from each of two source registers.

Description: 

rt = sign_extend((rt << 8*bp) || (rs >> 8*(4-bp)))

The right-most 32-bit word in register rt is left-shifted as a 32-bit value by bp byte positions, and the right-most word in register rs is right-shifted as a 32-bit value by (4-bp) byte positions. The shifted values are then or-ed together to create a 32-bit result that is sign-extended to 64 bits and written to destination register rt.

The argument bp is provided by the instruction, and is interpreted as an unsigned two-bit integer taking values between zero and three.

Restrictions:

No data-dependent exceptions are possible.

Operation: 

if (bp1..0 = 0) or (bp1..0 = 2) then
   GPR[rt]63..0 = UNPREDICTABLE
else 
   temp31..0 = ( GPR[rt]31..0 << (8*bp1..0) ) || ( GPR[rs]31..0 >> (8*(4-bp1..0)) )
   GPR[rt]63..0 = (temp31)32 || temp31..0
endif

Exceptions:

Reserved Instruction, DSP Disabled