CSC233 Assembly Language - CLC Instruction

CLC Instruction

The CLC (compare logical characters) instruction compares the first and second operands and sets the condition code to reflect the result of the comparison. The comparison is a logical comparison (not a numeric comparison), so it is used for character data. The two operands are compared bit by bit until a difference is found or until all bits are compared and the operands are found to be equal. The condition code is set as follows:

Relation of Operands	Result of Comparison	Value of Condition Code
operand1 == operand2	equal	00
operand1 < operand2	low	01
operand1 > operand2	high	10

Given the following definitions:

ONE      DC     C'ABCDE'
TWO      DC     C'12345'
THREE    DC     C'ABX1239'
FOUR     DC     C'ABC'
FIVE     DC     C'123'
SIX      DC     C' ABCD'
SEVEN    DC     C'BBC'

The DC statements shown above result in the following data (shown in character and hex) in storage:

A B C D E 1 2 3 4 5 A B X 1 2 3 9 A B C 1 2 3   A B C D B B C

C1C2C3C4C5F1F2F3F4F5C1C2E7F1F2F3F9C1C2C3F1F2F340C1C2C3C4C2C2C3

ONE       TWO       THREE         FOUR  FIVE  SIX       SEVEN

The following table shows the results of CLC instructions. Each instruction starts with the initial data given above.

CLC Instruction	Operand 1	Operand 2	Result	Condition Code
Implicit Comparisons
CLC ONE,TWO	C1C2C3C4C5	F1F2F3F4F5	low	01
CLC ONE,FOUR	C1C2C3C4C5	C1C2C3F1F2	low	01
CLC FOUR,ONE	C1C2C3	C1C2C3	equal	00
CLC SEVEN,FOUR	C2C2C3	C1C2C3	high	10
CLC FOUR,SIX+1	C1C2C3	C1C2C3	equal	00
CLC ONE,SIX	C1C2C3C4C5	40C1C2C3C4	high	10
CLC THREE,ONE	C1C2E7F1F2F3F9	C1C2C3C4C5F1F2	high	10
Explicit Comparisons
CLC TWO(3),FIVE	F1F2F3	F1F2F3	equal	00
CLC THREE+3(3),FIVE	F1F2F3	F1F2F3	equal	00
CLC FIVE(8),TWO	F1F2F340C1C2C3C4	F1F2F3F4F5C1C2E7	low	01
CLC SIX+2(1),SEVEN+1	C2	C2	equal	00