8051 Program - unsigned to signed conversion 32bit

; subroutine Mr0r3

; 32-Bit magnitude / Sign Bit -> 2's Complement Conversion

;

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

; Bits 21H & 22H = sign bits of operands X and Y

; (set if negative)

;

; output: r3, r2, r1, r0 = signed word

;

; alters: acc, C

Mr0r3:	jb 21H, Mr0r3b	;test X sign
	jb 22H, Mr0r3a	;test Y sign
	ret
Mr0r3b:	jnb 22H, Mr0r3a
	ret
Mr0r3a:	mov a, r0	;negate number
	cpl a	;complement
	add a, #1	;and add +1
	mov r0, a
	mov a, r1	;get next byte
	cpl a	;complement
	addc a, #0
	mov r1, a
	mov a, r2	;get next byte
	cpl a	;complement
	addc a, #0
	mov r2, a
	mov a, r3	;get next byte
	cpl a	;complement
	addc a, #0
	mov r3, a
	ret	;done

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

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

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List of topics: 8051

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