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#define	BDNZ	BC	16,0,
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#define	BDNE	BC	0,2,
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/*
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 *	mpvecsub(mpdigit *a, int alen, mpdigit *b, int blen, mpdigit *diff)
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 *
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 *		diff[0:alen-1] = a[0:alen-1] - b[0:blen-1]
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 *
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 *	prereq: alen >= blen, diff has room for alen digits
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 *
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 *		R3 == a
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 *		R4 == alen
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 *		R5 == b
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 *		R6 == blen
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 *		R7 == diff
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 *		R8 == temporary
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 *		R9 == temporary
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 */
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TEXT	mpvecsub(SB),$-4
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	MOVW	alen+4(FP),R4
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	MOVW	b+8(FP),R5
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	MOVW	blen+12(FP),R6
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	MOVW	diff+16(FP),R7
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	SUB	R6, R4		/* calculate counter for second loop (alen > blen) */
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	SUB	$4, R3		/* pre decrement for MOVWU's */
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	SUB	$4, R5		/* pre decrement for MOVWU's */
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	SUBC	$4, R7		/* pre decrement for MOVWU's and set carry */
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	/* skip subraction if b is zero */
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	CMP	R0,R6
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	BEQ	_sub1
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	/* diff[0:blen-1],borrow = a[0:blen-1] - b[0:blen-1] */
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	MOVW	R6, CTR
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_subloop1:
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	MOVWU	4(R3), R8
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	MOVWU	4(R5), R9
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	SUBE	R9, R8, R8
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	MOVWU	R8, 4(R7)
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	BDNZ	_subloop1
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_sub1:
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	/* skip subtraction if a is zero */
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	CMP	R0, R4
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	BEQ	_subend
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	/* diff[blen:alen-1] = a[blen:alen-1] - 0 + carry */
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	MOVW	R4, CTR
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_subloop2:
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	MOVWU	4(R3), R8
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	SUBE	R0, R8
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	MOVWU	R8, 4(R7)
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	BDNZ	_subloop2
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_subend:
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	RETURN
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