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29 September 1997 – Subject To Change
Introduction
1–3
The Architecture
1.1.2 Integer Data Types
Alpha architecture supports four integer data types.
Note:
Alpha implementations may impose a significant performance penalty
when accessing operands that are not NATURALLY ALIGNED. Refer
to the Alpha AXP Architecture Reference Manual for details.
1.1.3 Floating-Point Data Types
The 21164PC supports the following floating-point data types:
•
Longword integer format in floating-point unit
•
Quadword integer format in floating-point unit
•
IEEE floating-point formats
–
S_floating
–
T_floating
Data Type
Description
Byte
A byte is eight contiguous bits that start at an addressable byte boundary. A
byte is an 8-bit value. A byte is supported in Alpha architecture by the
EXTRACT, INSERT, LDBU, MASK, SEXTB, STB, ZAP, PACK,
UNPACK, MIN, MAX, and PERR instructions.
Word
A word is two contiguous bytes that start at an arbitrary byte boundary. A
word is a 16-bit value. A word is supported in Alpha architecture by the
EXTRACT, INSERT, LDWU, MASK, SEXTW, STW, PACK, UNPACK,
MIN, and MAX instructions.
Longword
A longword is four contiguous bytes that start at an arbitrary byte bound-
ary. A longword is a 32-bit value. A longword is supported in Alpha archi-
tecture by sign-extended load and store instructions and by longword
arithmetic instructions.
Quadword
A quadword is eight contiguous bytes that start at an arbitrary byte bound-
ary. A quadword is supported in Alpha architecture by load and store
instructions and quadword integer operate instructions.