PROGRAMMING WITH STREAMING SIMD EXTENSIONS 2 (SSE2)

11.3SSE2 DATA TYPES

SSE2 extensions introduced one 128-bit packed floating-point data type and four 128-bit SIMD integer data types to the IA-32 architecture (see Figure 11-2).

•Packed double-precision floating-point — This 128-bit data type consists of two IEEE 64-bit double-precision floating-point values packed into a double quadword. (See Figure 4-3 for the layout of a 64-bit double-precision floating-point value; refer to Section 4.2.2, “Floating-Point Data Types” for a detailed description of double-precision floating-point values.)

•128-bit packed integers — The four 128-bit packed integer data types can contain 16 byte integers, 8 word integers, 4 doubleword integers, or 2 quadword integers. (Refer to Section 4.6.2, “128-Bit Packed SIMD Data Types” for a detailed description of the 128-bit packed integers.)

128-Bit Packed Double-

Precision Floating-Point

Figure 11-2. Data Types Introduced with the SSE2 Extensions

All of these data types are operated on in XMM registers or memory. Instructions are provided to convert between these 128-bit data types and the 64-bit and 32-bit data types.

The address of a 128-bit packed memory operand must be aligned on a 16-byte boundary, except in the following cases:

•a MOVUPD instruction which supports unaligned accesses

•scalar instructions that use an 8-byte memory operand that is not subject to alignment requirements

Figure 4-2 shows the byte order of 128-bit (double quadword) and 64-bit (quadword) data types in memory.

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