Intel 64 and IA-32 Architectures Software Developers Manual Volume 1, Basic Architecture

Vol. 1 4-5
DATA TYPES
4.2.1 Integers
The Intel 64 and IA-32 architectures define two types of integers: unsigned and
signed. Unsigned integers are ordinary binary values ranging from 0 to the maximum
positive number that can be encoded in the selected operand size. Signed integers
are two’s complement binary values that can be used to represent both positive and
negative integer values.
Some integer instructions (such as the ADD, SUB, PADDB, and PSUBB instructions)
operate on either unsigned or signed integer operands. Other integer instructions
(such as IMUL, MUL, IDIV, DIV, FIADD, and FISUB) operate on only one integer type.
The following sections describe the encodings and ranges of the two types of
integers.
4.2.1.1 Unsigned Integers
Unsigned integers are unsigned binary numbers contained in a byte, word, double-
word, and quadword. Their values range from 0 to 255 for an unsigned byte integer,
from 0 to 65,535 for an unsigned word integer, from 0 to 2
32
– 1 for an unsigned
doubleword integer, and from 0 to 2
64
– 1 for an unsigned quadword integer.
Unsigned integers are sometimes referred to as ordinals.
4.2.1.2 Signed Integers
Signed integers are signed binary numbers held in a byte, word, doubleword, or
quadword. All operations on signed integers assume a two's complement representa-
tion. The sign bit is located in bit 7 in a byte integer, bit 15 in a word integer, bit 31 in
a doubleword integer, and bit 63 in a quadword integer (see the signed integer
encodings in Table 4-1).