Conditional Expressions

This document contains the following chapters:

• 1.0 Description
• 2.0 Simple Conditions
  • 2.1 Simple Condition Syntax 0 - mnemonic
  • 2.2 Simple Condition Syntax 1 - bit-fields
  • 2.3 Simple Condition Syntax 2 - NOT,bit-fields
  • 2.4 Simple Condition Syntax 3 - ANY,bit-fields
  • 2.5 Simple Condition Syntax 4 - field,mnemonic
  • 2.6 Simple Condition Syntax 5 - field1, relation,field2
  • 2.7 Simple Condition Syntax 6 - mnemonic, opcode,field1,field2
  • 2.8 Simple Condition Syntax 7 - code-value
  • 2.9 Simple Condition Syntax 8 - NOT,code-value
• 3.0 Complex Conditions
  • 3.1 Complex Condition Syntax 0 - Any simple condition
  • 3.2 Complex Condition Syntax 1 - ANDed conditions
  • 3.3 Complex Condition Syntax 2 - ORed conditions
  • 3.4 Complex Condition Syntax 3 - ANDed and ORed conditions
  • 3.5 Complex Condition Syntax 4 - Parenthesized conditions

1.0 Description

Conditional expressions are used by a variety of macros in Bixoft's eXtended Assembly Language. They basically appear as a sequence of operands - the exact number being variable - on the IF macro statement. Various other macros will accept a condition too, and if one is specified they internally generate an IF statement with the specified condition.
Some of these macros are:

The exact syntax of the conditional expressions is rather complicated. There are nine different basic formats. These basic formats evaluate as a simple condition.

These basic conditions can be combined into comlpex conditions by specifying several simple conditions, separating them with AND or OR keywords. Mixing AND and OR in a single complex conditional expression is not supported yet. The same holds for the use of parentheses to fix the order of evaluation.

2.0 Simple Conditions

2.1 Simple Condition Syntax 0

Simple conditions in format-0: Menmonic

2.2 Simple Condition Syntax 1

Simple conditions in format-1: one or more named bit-fields

2.3 Simple Condition Syntax 2

Simple conditions in format-2: NOT, one or more named bit-fields

2.4 Simple Condition Syntax 3

Simple conditions in format-3: ANY, one or more named bit-fields

2.5 Simple Condition Syntax 4

Simple conditions in format-4: field, mnemonic

2.6 Simple Condition Syntax 5

Simple conditions in format-5: field1, relation, field2

If the types or lengths of the operands are not equal, then one of the operands will be converted, if possible. E.g. when comparing a zoned field to signed or unsigned binary field or or to a register.

If the comparison cannot logically be made, an assembly error message will be issued. E.g. comparing a zoned field with an access register will not assemble.

2.7 Simple Condition Syntax 6

Simple conditions in format-6: mnemonic, opcode, field1, field2

2.8 Simple Condition Syntax 7

Simple conditions in format-7: named code-value

A code-field is like a bit field, in that it takes distinct values with separate meanings. E.g. a gender indication or an order status. Once each possible value has been defined the named code-values can be tested. E.g. MALE or BACKORDER.

2.9 Simple Condition Syntax 8

Simple conditions in format-8: NOT, named code-value

A code-field is like a bit field, in that it takes distinct values with separate meanings. E.g. a gender indication or an order status. Once each possible value has been defined the named code-values can be tested. E.g. MALE or BACKORDER.

3.0 Complex Conditions

3.1 Complex Condition Syntax 0

Complex conditions in format-0: Basic Condition

The format-0 Complex condition takes the form of a single basic condition in any of the nine formats specified above

3.2 Complex Condition Syntax 1

Complex conditions in format-1: AND-ed Basic Conditions

The format-1 Complex condition takes the form of multiple basic conditions, each in any of the nine formats specified above. The basic conditions are separated by the keyword AND. The condition will evaluate as true when each of the specified basic conditions is met.

Performance remark:
The basic conditions are evaluated from left to right, until one is found that does not match (if any). Therefore performance benefits if the condition that is most likely to evaluate as false is specified first.

3.3 Complex Condition Syntax 2

Complex conditions in format-2: OR-ed Basic Conditions

The format-2 Complex condition takes the form of multiple basic conditions, each in any of the nine formats specified above. The basic conditions are separated by the keyword OR. The condition will evaluate as true when any of the specified basic conditions is met.

Performance remark:
The basic conditions are evaluated from left to right, until one is found that does matches (if any). Therefore performance benefits if the condition that is most likely to evaluate as true is specified first.

3.4 Complex Condition Syntax 3

Complex conditions in format-3: AND-e and OR-ed Basic Conditions

This format has not yet been implemented. For the IF-macro this can be emulated by specifying OR-able basic conditions as a format-2 complex condition, while separating AND-able basic conditions into separate conditions

3.5 Complex Condition Syntax 4

Complex conditions in format-4: Parenthesized Basic Conditions

This format has not yet been implemented. For the IF-macro this can be emulated by specifying OR-able basic conditions as a format-2 complex condition, while separating AND-able basic conditions into separate conditions

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