| Opcode/Instruction | Op/En | 64/32-bit Mode | CPUID Feature Flag | Description |
| F3 0F 5F /r MAXSS xmm1, xmm2/m32 | RM | V/V | SSE | Return the maximum scalar single-precision floating-point value between xmm2/mem32 and xmm1. |
| VEX.NDS.LIG.F3.0F.WIG 5F /r VMAXSS xmm1, xmm2, xmm3/m32 | RVM | V/V | AVX | Return the maximum scalar single-precision floating-point value between xmm3/mem32 and xmm2. |
| 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 |
Compares the low single-precision floating-point values in the first source operand and the second source operand, and returns the maximum value to the low doubleword of the destination operand. If the values being compared are both 0.0s (of either sign), the value in the second source operand is returned. If a value in the second source operand is an SNaN, that SNaN is returned unchanged to the destination (that is, a QNaN version of the SNaN is not returned). If only one value is a NaN (SNaN or QNaN) for this instruction, the second source operand, either a NaN or a valid floating-point value, is written to the result. If instead of this behavior, it is required that the NaN from either source operand be returned, the action of MAXSS can be emulated using a sequence of instructions, such as, a comparison followed by AND, ANDN and OR. The second source operand can be an XMM register or a 32-bit memory location. The first source and destination operands are XMM registers.
In 64-bit mode, use of the REX.R prefix permits this instruction to access additional registers (XMM8-XMM15). 128-bit Legacy SSE version: The destination and first source operand are the same. Bits (VLMAX-1:32) of the corresponding YMM destination register remain unchanged. VEX.128 encoded version: Bits (127:32) of the XMM register destination are copied from corresponding bits in the first source operand. Bits (VLMAX-1:128) of the destination YMM register are zeroed.
MAX(SRC1, SRC2)
{
IF ((SRC1 = 0.0) and (SRC2 = 0.0)) THEN DEST ← SRC2;
ELSE IF (SRC1 = SNaN) THEN DEST ← SRC2; FI;
ELSE IF SRC2 = SNaN) THEN DEST ← SRC2; FI;
ELSE IF (SRC1 > SRC2) THEN DEST ← SRC1;
ELSE DEST ← SRC2;
FI;
}
MAXSS (128-bit Legacy SSE version)
DEST[31:0] ←MAX(DEST[31:0], SRC[31:0])
DEST[VLMAX-1:32] (Unmodified)
VMAXSS (VEX.128 encoded version)
DEST[31:0] ←MAX(SRC1[31:0], SRC2[31:0])
DEST[127:32] ←SRC1[127:32]
DEST[VLMAX-1:128] ← 0
__m128d _mm_max_ss(__m128d a, __m128d b)
Invalid (including QNaN source operand), Denormal.
See Exceptions Type 3.