Programmer’s Model
ARM DDI 0301H Copyright © 2004-2009 ARM Limited. All rights reserved. 2-14
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2.5 Data types
The processor supports the following data types:
• word, 32-bit
• halfword, 16-bit
• byte, 8-bit.
Note
• When any of these types are described as unsigned, the N-bit data value represents a
non-negative integer in the range 0 to +2
N
-1, using normal binary format.
• When any of these types are described as signed, the N-bit data value represents an integer
in the range -2
N-1
to +2
N-1
-1, using two’s complement format.
For best performance you must align these as follows:
• word quantities must be aligned to four-byte boundaries
• halfword quantities must be aligned to two-byte boundaries
• byte quantities can be placed on any byte boundary.
The processor provides mixed-endian and unaligned access support. For details see Chapter 4
Unaligned and Mixed-endian Data Access Support.
Note
You cannot use LDRD, LDM, LDC, STRD, STM, or STC instructions to access 32-bit
quantities if they are unaligned.
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