Intel 253666-024US - Manual (Page 623)

Vol. 2A 3-577
INSTRUCTION SET REFERENCE, A-M
MAXSD—Return Maximum Scalar Double-Precision Floating-Point Value
MAXSD—Return Maximum Scalar Double-Precision Floating-Point
Value
Description
Compares the low double-precision floating-point values in the destination operand
(first operand) and the source operand (second operand), and returns the maximum
value to the low quadword of the destination operand. The source operand can be an
XMM register or a 64-bit memory location. The destination operand is an XMM
register. When the source operand is a memory operand, only 64 bits are accessed.
The high quadword of the destination operand remains unchanged.
If the values being compared are both 0.0s (of either sign), the value in the second
operand (source operand) is returned. If a value in the second 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 operand
(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 source operand (from either the
first or second operand) be returned, the action of MAXSD can be emulated using a
sequence of instructions, such as, a comparison followed by AND, ANDN and OR.
In 64-bit mode, use of the REX.R prefix permits this instruction to access additional
registers (XMM8-XMM15).
Operation
DEST[63:0] ← IF ((DEST[63:0] = 0.0) and (SRC[63:0] = 0.0))
THEN SRC[63:0]; FI;
IF (DEST[63:0] = SNaN)
THEN SRC[63:0];
ELSE IF (SRC[63:0] = SNaN)
THEN SRC[63:0]; FI;
ELSE IF (DEST[63:0] > SRC[63:0])
THEN DEST[63:0];
ELSE SRC[63:0]; FI; FI;
(* DEST[127:64] is unchanged *);
Opcode Instruction 64-Bit
Mode
Compat/
Leg Mode
Description
F2 0F 5F /r MAXSD xmm1,
xmm2/m64
Valid Valid Return the maximum scalar double-
precision floating-point value
between xmm2/mem64 and xmm1.