PALIGNR — Packed Align Right

NOTES:

1. See note in Section 2.4, “Instruction Exception Specification” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A and Section 22.25.3, “Exception Conditions of Legacy SIMD Instructions Operating on MMX Registers” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A.

Instruction Operand Encoding

Description

(V)PALIGNR concatenates the destination operand (the first operand) and the source operand (the second operand) into an intermediate composite, shifts the composite at byte granularity to the right by a constant imme-diate, and extracts the right-aligned result into the destination. The first and the second operands can be an MMX, XMM or a YMM register. The immediate value is considered unsigned. Immediate shift counts larger than the 2L (i.e. 32 for 128-bit operands, or 16 for 64-bit operands) produce a zero result. Both operands can be MMX regis-ters, XMM registers or YMM registers. When the source operand is a 128-bit memory operand, the operand must be aligned on a 16-byte boundary or a general-protection exception (#GP) will be generated.

In 64-bit mode, use the REX prefix to access additional registers.

128-bit Legacy SSE version: Bits (VLMAX-1:128) of the corresponding YMM destination register remain unchanged.

VEX.128 encoded version: The first source operand is an XMM register. The second source operand is an XMM register or 128-bit memory location. The destination operand is an XMM register. The upper bits (VLMAX-1:128) of the corresponding YMM register destination are zeroed.

VEX.256 encoded version: The first source operand is a YMM register and contains two 16-byte blocks. The second source operand is a YMM register or a 256-bit memory location containing two 16-byte block. The destination operand is a YMM register and contain two 16-byte results. The imm8[7:0] is the common shift count used for the two lower 16-byte block sources and the two upper 16-byte block sources. The low 16-byte block of the two source

operands produce the low 16-byte result of the destination operand, the high 16-byte block of the two source oper-ands produce the high 16-byte result of the destination operand.

Concatenation is done with 128-bit data in the first and second source operand for both 128-bit and 256-bit instructions. The high 128-bits of the intermediate composite 256-bit result came from the 128-bit data from the first source operand; the low 128-bits of the intermediate result came from the 128-bit data of the second source operand.

Note: VEX.L must be 0, otherwise the instruction will #UD.

0

127

0

127

SRC1

SRC2

Imm8[7:0]*8

255

128

128

255

SRC1

SRC2

Imm8[7:0]*8

127

0

128

255

DEST

DEST

Figure 4-3. 256-bit VPALIGN Instruction Operation

Operation

PALIGNR (with 64-bit operands)

    temp1[127:0] = CONCATENATE(DEST,SRC)>>(imm8*8)
    DEST[63:0] = temp1[63:0]

PALIGNR (with 128-bit operands)

temp1[255:0] ← ((DEST[127:0] << 128) OR SRC[127:0])>>(imm8*8);
DEST[127:0] ← temp1[127:0]
DEST[VLMAX-1:128] (Unmodified)

VPALIGNR (VEX.128 encoded version)

temp1[255:0] ← ((SRC1[127:0] << 128) OR SRC2[127:0])>>(imm8*8);
DEST[127:0] ← temp1[127:0]
DEST[VLMAX-1:128] ← 0

VPALIGNR (VEX.256 encoded version)

temp1[255:0] ← ((SRC1[127:0] << 128) OR SRC2[127:0])>>(imm8[7:0]*8);
DEST[127:0] ← temp1[127:0]
temp1[255:0] ← ((SRC1[255:128] << 128) OR SRC2[255:128])>>(imm8[7:0]*8);
DEST[255:128] ← temp1[127:0]

Intel C/C++ Compiler Intrinsic Equivalents

PALIGNR:

__m64 _mm_alignr_pi8 (__m64 a, __m64 b, int n)

(V)PALIGNR:

__m128i _mm_alignr_epi8 (__m128i a, __m128i b, int n)

VPALIGNR:

__m256i _mm256_alignr_epi8 (__m256i a, __m256i b, const int n)

SIMD Floating-Point Exceptions

None.

Other Exceptions

See Exceptions Type 4; additionally