ST20-C1 datasheet(11/205 Pages) STMICROELECTRONICS

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2 Notation

represent an address which is offset by

x words (4x bytes) from the address in

Areg

′← word[Areg @ n]

Here, Areg is loaded with the contents of the word that is n words from the address

pointed to by Areg, i.e. the word at address Areg

+ 4n.

In all cases, if the given base address has the correct alignment then any offset used

will also give a correctly aligned address.

2.3

Operators used in the definitions

A full list of the operators used in the instruction definitions is given in Table 2.1.

Unless otherwise stated, all arithmetic is signed.

Modulo operators

Arithmetic is done using

modulo arithmetic — i.e. there is no checking for errors and, if

the calculation overflows, the result ‘wraps around’ the range of values representable

in the word length of the processor — e.g. adding 1 to the address at the top of the

Symbol

Meaning

Unchecked (modulo) integer arithmetic

−

rem

Signed integer add, subtract, multiply, divide and remainder. If the computation

overflows the result of the operation is truncated to the word length. If a divide

or remainder by zero occurs the result of the operation is undefined. No errors

are signalled. The operator ‘

−’ is also used as a monadic operator.

Signed comparison operators

≤

≥

≠

Comparisons of signed integer values: ‘less than’, ‘greater than’, ‘less than or

equal’, ‘greater than or equal’, ‘equal’ and ‘not equal’.

Bitwise operators

∼

∧

∨

⊗

>>arith

‘Not’, ‘and’, ‘or’, ‘exclusive or’, logical left and right shift and arithmetic right shift

operations on bits in words.

Boolean operators

not

and

Boolean combination in conditionals.

Table 2.1 Operators used in the instruction descriptions

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