ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Unary plus, minus and absolute value
Pseudocode Definition
If x is an integer or real, then +x is x unchanged, -x is x with its sign reversed, and Abs(x) is the absolute value
of x. All three are of the same type as x.
Addition and subtraction
If x and y are integers or reals, x+y and x-y are their sum and difference. Both are of type integer if x and y
are both of type integer, and real otherwise.
Addition and subtraction are particularly common arithmetic operations in pseudocode, and so it is also
convenient to have definitions of addition and subtraction acting directly on bitstring operands.
If x and y are bitstrings of the same length N = Len(x) = Len(y), then x+y and x-y are the least significant N
bits of the results of converting them to integers and adding or subtracting them. Signed and unsigned
conversions produce the same result:
x+y = (SInt(x) + SInt(y))
= (UInt(x) + UInt(y))
x-y = (SInt(x) - SInt(y))
= (UInt(x) - UInt(y))
If x is a bitstring of length N and y is an integer, x+y and x-y are the bitstrings of length N defined by x+y = x
+ y and x-y = x - y. Similarly, if x is an integer and y is a bitstring of length M, x+y and x-y
are the bitstrings of length M defined by x+y = x + y and x-y = x - y.
Comparisons
If x and y are integers or reals, then x == y, x != y, x < y, x y, and x >= y are equal, not equal,
less than, less than or equal, greater than, and greater than or equal comparisons between them, producing
boolean results. In the case of == and !=, this extends the generic definition applying to any two values of
the same type to also act between integers and reals.
Multiplication
If x and y are integers or reals, then x * y is the product of x and y, of type integer if both x and y are of type
integer and otherwise of type real.
Division and modulo
If x and y are integers or reals, then x / y is the result of dividing x by y, and is always of type real.
If x and y are integers, then x DIV y and x MOD y are defined by:
x DIV y = RoundDown(x / y)
x MOD y = x - y * (x DIV y)
It is a pseudocode error to use any x / y, x MOD y, or x DIV y in any context where y can be zero.
ARM DDI 0406B Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. AppxI-15