8051 Program - signed 32bit subtraction

; subroutine SUB32

; 32-Bit Signed (2's Complement) subtraction

;

; input: r3, r2, r1, r0 = X

; r7, r6, r5, r4 = Y

;

; output: r3, r2, r1, r0 = signed difference D = X - Y

; Carry C is set if the result (D) is out of range.

;

; alters: acc, C, OV

SUB32:	anl PSW, #0E7H	;Register Bank 0
	mov a, r0	;load X low byte into acc
	clr C	;clear carry flag
	subb a, r4	;subract Y low byte
	mov r0, a	;put result in Z low byte
	mov a, r1	;repeat with other bytes...
	subb a, r5
	mov r1, a
	mov a, r2
	subb a, r6
	mov r2, a
	mov a, r3
	subb a, r7
	mov r3, a
	mov C, OV	;set C if external borrow
	ret

Source: Maths Subroutines for the 8051 microcontroller, W.G.Marshall 2002

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Related topics:
8051 Program - signed 16bit addition   |   8051 Program - signed 32bit addition   |   8051 Program - signed 16bit subtraction   |   8051 Program - signed 32bit subtraction   |   8051 Program - signed 8bit multiplication   |   8051 Program - unsigned 8bit multiplication   |   8051 Program - memory subroutines   |   8051 Program - math subroutines   |   8051 Program - conversion subroutines

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List of topics: 8051

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