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Figure 4-5. Pointers in 64-Bit Mode

4.4BIT FIELD DATA TYPE

A bit field (see Figure 4-6) is a contiguous sequence of bits. It can begin at any bit position of any byte in memory and can contain up to 32 bits.

Bit Field

Field Length

Least

Significant

Bit

Figure 4-6. Bit Field Data Type

4.5STRING DATA TYPES

Strings are continuous sequences of bits, bytes, words, or doublewords. A bit string can begin at any bit position of any byte and can contain up to 232 –1 bits. A byte string can contain bytes, words, or doublewords and can range from zero to 232 – 1 bytes (4 GBytes).

4.6PACKED SIMD DATA TYPES

IA-32 architecture defines and operates on a set of 64-bit and 128-bit packed data type for use in SIMD operations. These data types consist of fundamental data types (packed bytes, words, doublewords, and quadwords) and numeric interpretations of fundamental types for use in packed integer and packed floating-point operations.

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4.6.164-Bit SIMD Packed Data Types

The 64-bit packed SIMD data types were introduced into the IA-32 architecture in the Intel MMX technology. They are operated on in MMX registers. The fundamental 64-bit packed data types are packed bytes, packed words, and packed doublewords (see Figure 4-7). When performing numeric SIMD operations on these data types, these data types are interpreted as containing byte, word, or doubleword integer values.

4.6.2 128-Bit Packed SIMD Data Types

The 128-bit packed SIMD data types were introduced into the IA-32 architecture in the SSE extensions and used with SSE2 and SSE3 extensions. They are operated on primarily in the 128-bit XMM registers and memory. The fundamental 128-bit packed data types are packed bytes, packed words, packed doublewords, and packed quadwords (see Figure 4-8). When performing SIMD operations on these fundamental data types in XMM registers, these data types are interpreted as containing packed or scalar single-precision floating-point or doubleprecision floating-point values, or as containing packed byte, word, doubleword, or quadword integer values.

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