PSRAW/PSRAD—Shift Packed Data Right Arithmetic

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

Shifts the bits in the individual data elements (words or doublewords) in the destination operand (first operand) to the right by the number of bits specified in the count operand (second operand). As the bits in the data elements are shifted right, the empty high-order bits are filled with the initial value of the sign bit of the data element. If the value specified by the count operand is greater than 15 (for words) or 31 (for doublewords), each destination data element is filled with the initial value of the sign bit of the element. (Figure 4-14 gives an example of shifting words in a 64-bit operand.)

Figure 4-14. PSRAW and PSRAD Instruction Operation Using a 64-bit Operand

Note that only the first 64-bits of a 128-bit count operand are checked to compute the count. If the second source operand is a memory address, 128 bits are loaded.

The (V)PSRAW instruction shifts each of the words in the destination operand to the right by the number of bits specified in the count operand, and the (V)PSRAD instruction shifts each of the doublewords in the destination operand.

In 64-bit mode, using a REX prefix in the form of REX.R permits this instruction to access additional registers (XMM8-XMM15).

Legacy SSE instructions: The destination operand is an MMX technology register; the count operand can be either an MMX technology register or an 64-bit memory location.

128-bit Legacy SSE version: The destination and first source operands are XMM registers. Bits (VLMAX-1:128) of the corresponding YMM destination register remain unchanged. The count operand can be either an XMM register or a 128-bit memory location or an 8-bit immediate. If the count operand is a memory address, 128 bits are loaded but the upper 64 bits are ignored.

VEX.128 encoded version: The destination and first source operands are XMM registers. Bits (VLMAX-1:128) of the destination YMM register are zeroed. The count operand can be either an XMM register or a 128-bit memory loca-tion or an 8-bit immediate. If the count operand is a memory address, 128 bits are loaded but the upper 64 bits are ignored.

VEX.256 encoded version: The destination and first source operands are YMM registers. The count operand can be either an XMM register or a 128-bit memory location or an 8-bit immediate.

Note: For shifts with an immediate count (VEX.128.66.0F 71-73 /4), VEX.vvvv encodes the destination register, and VEX.B + ModRM.r/m encodes the source register. VEX.L must be 0, otherwise instructions will #UD.

Operation

PSRAW (with 64-bit operand)

    IF (COUNT > 15)
         THEN COUNT ← 16;
    FI;
    DEST[15:0] ← SignExtend(DEST[15:0] >> COUNT);
    (* Repeat shift operation for 2nd and 3rd words *)
    DEST[63:48] ← SignExtend(DEST[63:48] >> COUNT);

PSRAD (with 64-bit operand)

    IF (COUNT > 31)
         THEN COUNT ← 32;
    FI;
    DEST[31:0] ← SignExtend(DEST[31:0] >> COUNT);
    DEST[63:32] ← SignExtend(DEST[63:32] >> COUNT);

PSRAW (with 128-bit operand)

    COUNT ← COUNT_SOURCE[63:0];
    IF (COUNT > 15)
         THEN COUNT ← 16;
    FI;
    DEST[15:0]  ← SignExtend(DEST[15:0] >> COUNT);
    (* Repeat shift operation for 2nd through 7th words *)
    DEST[127:112] ← SignExtend(DEST[127:112] >> COUNT);

PSRAD (with 128-bit operand)

    COUNT ← COUNT_SOURCE[63:0];
    IF (COUNT > 31)
         THEN COUNT ← 32;
    FI;
    DEST[31:0]  ← SignExtend(DEST[31:0] >> COUNT);
    (* Repeat shift operation for 2nd and 3rd doublewords *)
    DEST[127:96] ← SignExtend(DEST[127:96] >>COUNT);

PSRAW (xmm, xmm, xmm/m128)

DEST[127:0] ← ARITHMETIC_RIGHT_SHIFT_WORDS(DEST, SRC)
DEST[VLMAX-1:128] (Unmodified)

PSRAW (xmm, imm8)

DEST[127:0] ← ARITHMETIC_RIGHT_SHIFT_WORDS(DEST, imm8)
DEST[VLMAX-1:128] (Unmodified)

VPSRAW (xmm, xmm, xmm/m128)

DEST[127:0] ← ARITHMETIC_RIGHT_SHIFT_WORDS(SRC1, SRC2)
DEST[VLMAX-1:128] ← 0

VPSRAW (xmm, imm8)

DEST[127:0] ← ARITHMETIC_RIGHT_SHIFT_WORDS(SRC1, imm8)
DEST[VLMAX-1:128] ← 0

PSRAD (xmm, xmm, xmm/m128)

DEST[127:0] ← ARITHMETIC_RIGHT_SHIFT_DWORDS(DEST, SRC)
DEST[VLMAX-1:128] (Unmodified)

PSRAD (xmm, imm8)

DEST[127:0] ← ARITHMETIC_RIGHT_SHIFT_DWORDS(DEST, imm8)
DEST[VLMAX-1:128] (Unmodified)

VPSRAD (xmm, xmm, xmm/m128)

DEST[127:0] ← ARITHMETIC_RIGHT_SHIFT_DWORDS(SRC1, SRC2)
DEST[VLMAX-1:128] ← 0

VPSRAD (xmm, imm8)

DEST[127:0] ← ARITHMETIC_RIGHT_SHIFT_DWORDS(SRC1, imm8)
DEST[VLMAX-1:128] ← 0

VPSRAW (ymm, ymm, xmm/m128)

DEST[255:0] ← ARITHMETIC_RIGHT_SHIFT_WORDS_256b(SRC1, SRC2)

VPSRAW (ymm, imm8)

DEST[255:0] ← ARITHMETIC_RIGHT_SHIFT_WORDS_256b(SRC1, imm8)

VPSRAD (ymm, ymm, xmm/m128)

DEST[255:0] ← ARITHMETIC_RIGHT_SHIFT_DWORDS_256b(SRC1, SRC2)

VPSRAD (ymm, imm8)

DEST[255:0] ← ARITHMETIC_RIGHT_SHIFT_DWORDS_256b(SRC1, imm8)

Intel C/C++ Compiler Intrinsic Equivalents

PSRAW:

__m64 _mm_srai_pi16 (__m64 m, int count)

PSRAW:

__m64 _mm_sra_pi16 (__m64 m, __m64 count)

(V)PSRAW:

__m128i _mm_srai_epi16(__m128i m, int count)

(V)PSRAW:

__m128i _mm_sra_epi16(__m128i m, __m128i count)

VPSRAW:

__m256i _mm256_srai_epi16 (__m256i m, int count)

VPSRAW:

__m256i _mm256_sra_epi16 (__m256i m, __m128i count)

PSRAD:

__m64 _mm_srai_pi32 (__m64 m, int count)

PSRAD:

__m64 _mm_sra_pi32 (__m64 m, __m64 count)

(V)PSRAD:

__m128i _mm_srai_epi32 (__m128i m, int count)

(V)PSRAD:

__m128i _mm_sra_epi32 (__m128i m, __m128i count)

VPSRAD:

__m256i _mm256_srai_epi32 (__m256i m, int count)

VPSRAD:

__m256i _mm256_sra_epi32 (__m256i m, __m128i count)

Flags Affected

None.

Numeric Exceptions

None.

Other Exceptions

See Exceptions Type 4 and 7 for non-VEX-encoded instructions; additionally