PMAXSB (Maximum of Packed Signed Byte Integers)

Opcodes

Opcode/Instruction Op/En 64/32 bit Mode Support CPUID Feature Flag Description
66 0F 38 3C /r PMAXSB xmm1, xmm2/m128 RM V/V SSE4_1 Compare packed signed byte integers in xmm1 and xmm2/m128 and store packed maximum values in xmm1.
VEX.NDS.128.66.0F38.WIG 3C /r VPMAXSB xmm1, xmm2, xmm3/m128 RVM V/V AVX Compare packed signed byte integers in xmm2 and xmm3/m128 and store packed maximum values in xmm1.
VEX.NDS.256.66.0F38.WIG 3C /r VPMAXSB ymm1, ymm2, ymm3/m256 RVM V/V AVX2 Compare packed signed byte integers in ymm2 and ymm3/m128 and store packed maximum values in ymm1.

Instruction Operand Encoding

Op/En Operand 1 Operand 2 Operand 3 Operand 4
RM ModRM:reg (r, w) ModRM:r/m (r) NA NA
RVM ModRM:reg (w) VEX.vvvv (r) ModRM:r/m (r) NA

Description

Compares packed signed byte integers in the destination operand (first operand) and the source operand (second operand), and returns the maximum for each packed value in the destination operand.

128-bit Legacy SSE version: The first source and destination operands are XMM registers. The second source operand is an XMM register or a 128-bit memory location. Bits (VLMAX-1:128) of the corresponding YMM destina-tion register remain unchanged.

VEX.128 encoded version: The first source and destination operands are XMM registers. The second source operand is an XMM register or a 128-bit memory location. Bits (VLMAX-1:128) of the destination YMM register are zeroed.

VEX.256 encoded version: The second source operand can be an YMM register or a 256-bit memory location. The first source and destination operands are YMM registers.

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

Operation

IF (DEST[7:0] 
 SRC[7:0])
    THEN DEST[7:0] ← DEST[7:0];
    ELSE DEST[7:0] ← SRC[7:0]; FI;
IF (DEST[15:8] 
 SRC[15:8])
    THEN DEST[15:8] ← DEST[15:8];
    ELSE DEST[15:8] ← SRC[15:8]; FI;
IF (DEST[23:16] 
 SRC[23:16])
    THEN DEST[23:16] ← DEST[23:16];
    ELSE DEST[23:16] ← SRC[23:16]; FI;
IF (DEST[31:24] 
 SRC[31:24])
    THEN DEST[31:24] ← DEST[31:24];
    ELSE DEST[31:24] ← SRC[31:24]; FI;
IF (DEST[39:32] 
 SRC[39:32])
    THEN DEST[39:32] ← DEST[39:32];
    ELSE DEST[39:32] ← SRC[39:32]; FI;
IF (DEST[47:40] 
 SRC[47:40])
    THEN DEST[47:40] ← DEST[47:40];
    ELSE DEST[47:40] ← SRC[47:40]; FI;
IF (DEST[55:48] 
 SRC[55:48])
    THEN DEST[55:48] ← DEST[55:48];
    ELSE DEST[55:48] ← SRC[55:48]; FI;
IF (DEST[63:56] 
 SRC[63:56])
    THEN DEST[63:56] ← DEST[63:56];
    ELSE DEST[63:56] ← SRC[63:56]; FI;
IF (DEST[71:64] 
 SRC[71:64])
    THEN DEST[71:64] ← DEST[71:64];
    ELSE DEST[71:64] ← SRC[71:64]; FI;
IF (DEST[79:72] 
 SRC[79:72])
    THEN DEST[79:72] ← DEST[79:72];
    ELSE DEST[79:72] ← SRC[79:72]; FI;
IF (DEST[87:80] 
 SRC[87:80])
    THEN DEST[87:80] ← DEST[87:80];
    ELSE DEST[87:80] ← SRC[87:80]; FI;
IF (DEST[95:88] 
 SRC[95:88])
    THEN DEST[95:88] ← DEST[95:88];
    ELSE DEST[95:88] ← SRC[95:88]; FI;
IF (DEST[103:96] 
 SRC[103:96])
    THEN DEST[103:96] ← DEST[103:96];
    ELSE DEST[103:96] ← SRC[103:96]; FI;
IF (DEST[111:104] 
 SRC[111:104])
    THEN DEST[111:104] ← DEST[111:104];
    ELSE DEST[111:104] ← SRC[111:104]; FI;
IF (DEST[119:112] 
 SRC[119:112])
    THEN DEST[119:112] ← DEST[119:112];
    ELSE DEST[119:112] ← SRC[119:112]; FI;
IF (DEST[127:120] 
 SRC[127:120])
    THEN DEST[127:120] ← DEST[127:120];
    ELSE DEST[127:120] ← SRC[127:120]; FI;

VPMAXSB (VEX.128 encoded version)

    IF SRC1[7:0] 
SRC2[7:0] THEN
         DEST[7:0] ← SRC1[7:0];
    ELSE
         DEST[7:0] ← SRC2[7:0]; FI;
    (* Repeat operation for 2nd through 15th bytes in source and destination operands *)
    IF SRC1[127:120] 
SRC2[127:120] THEN
         DEST[127:120] ← SRC1[127:120];
    ELSE
         DEST[127:120] ← SRC2[127:120]; FI;
DEST[VLMAX-1:128] ← 0

VPMAXSB (VEX.256 encoded version)

    IF SRC1[7:0] 
SRC2[7:0] THEN
         DEST[7:0] ← SRC1[7:0];
    ELSE
         DEST[15:0] ← SRC2[7:0]; FI;
    (* Repeat operation for 2nd through 31st bytes in source and destination operands *)
    IF SRC1[255:248] 
SRC2[255:248] THEN
         DEST[255:248] ← SRC1[255:248];
    ELSE
         DEST[255:248] ← SRC2[255:248]; FI;

Intel C/C++ Compiler Intrinsic Equivalent

(V)PMAXSB:

__m128i _mm_max_epi8 ( __m128i a, __m128i b);

VPMAXSB:

__m256i _mm256_max_epi8 ( __m256i a, __m256i b);

Flags Affected

None.

SIMD Floating-Point Exceptions

None.

Other Exceptions

See Exceptions Type 4; additionally

#UD If VEX.L = 1.