ev67-strlen_user.s

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/*
 * arch/alpha/lib/ev67-strlen_user.S
 * 21264 version contributed by Rick Gorton <[e-mail]>
 *
 * Return the length of the string including the NULL terminator
 * (strlen+1) or zero if an error occurred.
 *
 * In places where it is critical to limit the processing time,
 * and the data is not trusted, strnlen_user() should be used.
 * It will return a value greater than its second argument if
 * that limit would be exceeded. This implementation is allowed
 * to access memory beyond the limit, but will not cross a page
 * boundary when doing so.
 *
 * Much of the information about 21264 scheduling/coding comes from:
 *      Compiler Writer's Guide for the Alpha 21264
 *      abbreviated as 'CWG' in other comments here
 *      ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
 * Scheduling notation:
 *      E       - either cluster
 *      U       - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
 *      L       - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
 * Try not to change the actual algorithm if possible for consistency.
 */

#include <alpha/regdef.h>


/* Allow an exception for an insn; exit if we get one.  */
#define EX(x,y...)			\
	99: x,##y;			\
	.section __ex_table,"a";	\
	.gprel32 99b;			\
	lda v0, $exception-99b(zero);	\
	.previous


	.set noreorder
	.set noat
	.text

	.globl __strlen_user
	.ent __strlen_user
	.frame sp, 0, ra

	.align 4
__strlen_user:
	ldah	a1, 32767(zero)	# do not use plain strlen_user() for strings
				# that might be almost 2 GB long; you should
				# be using strnlen_user() instead
	nop
	nop
	nop

	.globl __strnlen_user

	.align 4
__strnlen_user:
	ldgp	$29,0($27)	# E E : we do exceptions -- we need the gp.
				/* Decomposes into lda/ldah */
	.prologue 1
	EX( ldq_u t0, 0(a0) )	# L : load first quadword (a0 may be misaligned)
	lda     t1, -1(zero)	# E :

	insqh   t1, a0, t1	# U :
	andnot  a0, 7, v0	# E :
	or      t1, t0, t0	# E :
	subq	a0, 1, a0	# E : get our +1 for the return 

	cmpbge  zero, t0, t1	# E : t1 <- bitmask: bit i == 1 <==> i-th byte == 0
	subq	a1, 7, t2	# E :
	subq	a0, v0, t0	# E :
	bne     t1, $found	# U :

	addq	t2, t0, t2	# E :
	addq	a1, 1, a1	# E :
	nop			# E :
	nop			# E :

	.align 4
$loop:	ble	t2, $limit	# U :
	EX( ldq t0, 8(v0) )	# L :
	nop			# E :
	nop			# E :

	cmpbge  zero, t0, t1	# E :
	subq	t2, 8, t2	# E :
	addq    v0, 8, v0	# E : addr += 8
	beq     t1, $loop	# U :

$found: cttz	t1, t2		# U0 :
	addq	v0, t2, v0	# E :
	subq    v0, a0, v0	# E :
	ret			# L0 :

$exception:
	nop
	nop
	nop
	ret

	.align 4		# currently redundant
$limit:
	nop
	nop
	subq	a1, t2, v0
	ret

	.end __strlen_user