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awilliam
GitHub Repository: awilliam/linux-vfio
 Path: blob/master/arch/alpha/lib/ev67-strncat.S
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/*

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 * arch/alpha/lib/ev67-strncat.S

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 * 21264 version contributed by Rick Gorton <[email protected]>

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 *

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 * Append no more than COUNT characters from the null-terminated string SRC

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 * to the null-terminated string DST.  Always null-terminate the new DST.

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 *

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 * This differs slightly from the semantics in libc in that we never write

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 * past count, whereas libc may write to count+1.  This follows the generic

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 * implementation in lib/string.c and is, IMHO, more sensible.

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 *

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 * Much of the information about 21264 scheduling/coding comes from:

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 *	Compiler Writer's Guide for the Alpha 21264

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 *	abbreviated as 'CWG' in other comments here

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 *	ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html

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 * Scheduling notation:

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 *	E	- either cluster

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 *	U	- upper subcluster; U0 - subcluster U0; U1 - subcluster U1

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 *	L	- lower subcluster; L0 - subcluster L0; L1 - subcluster L1

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 * Try not to change the actual algorithm if possible for consistency.

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 */

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	.text

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	.align 4

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	.globl strncat

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	.ent strncat

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strncat:

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	.frame $30, 0, $26

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	.prologue 0

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	mov	$16, $0		# set up return value

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	beq	$18, $zerocount	# U :

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	/* Find the end of the string.  */

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	ldq_u   $1, 0($16)	# L : load first quadword ($16 may be misaligned)

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	lda     $2, -1($31)	# E :

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	insqh   $2, $0, $2	# U :

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	andnot  $16, 7, $16	# E :

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	nop			# E :

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	or      $2, $1, $1	# E :

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	nop			# E :

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	nop			# E :

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	cmpbge  $31, $1, $2	# E : bits set iff byte == 0

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	bne     $2, $found	# U :

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$loop:	ldq     $1, 8($16)	# L :

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	addq    $16, 8, $16	# E :

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	cmpbge  $31, $1, $2	# E :

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	beq     $2, $loop	# U :

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$found:	cttz	$2, $3		# U0 :

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	addq	$16, $3, $16	# E :

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	nop			# E :

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	bsr	$23, __stxncpy	# L0 :/* Now do the append.  */

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	/* Worry about the null termination.  */

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	zapnot	$1, $27, $2	# U : was last byte a null?

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	cmplt	$27, $24, $5	# E : did we fill the buffer completely?

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	bne	$2, 0f		# U :

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	ret			# L0 :

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0:	or	$5, $18, $2	# E :

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	nop

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	bne	$2, 2f		# U :

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	and	$24, 0x80, $3	# E : no zero next byte

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	nop			# E :

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	bne	$3, 1f		# U :

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	/* Here there are bytes left in the current word.  Clear one.  */

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	addq	$24, $24, $24	# E : end-of-count bit <<= 1

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	nop			# E :

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2:	zap	$1, $24, $1	# U :

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	nop			# E :

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	stq_u	$1, 0($16)	# L :

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	ret			# L0 :

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1:	/* Here we must clear the first byte of the next DST word */

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	stb	$31, 8($16)	# L :

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	nop			# E :

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	nop			# E :

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	ret			# L0 :

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$zerocount:

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	nop			# E :

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	nop			# E :

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	nop			# E :

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	ret			# L0 :

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	.end strncat

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