patch-2.1.5 linux/arch/alpha/lib/stxcpy.S

• Lines: 289
• Date: Fri Oct 18 11:53:20 1996
• Orig file: v2.1.4/linux/arch/alpha/lib/stxcpy.S
• Orig date: Thu Jan 1 02:00:00 1970

diff -u --recursive --new-file v2.1.4/linux/arch/alpha/lib/stxcpy.S linux/arch/alpha/lib/stxcpy.S
@@ -0,0 +1,288 @@
+/* stxcpy.S
+ * Contributed by Richard Henderson (rth@tamu.edu)
+ *
+ * Copy a null-terminated string from SRC to DST.
+ *
+ * This is an internal routine used by strcpy, stpcpy, and strcat.
+ * As such, it uses special linkage conventions to make implementation
+ * of these public functions more efficient.
+ *
+ * On input:
+ *	t9 = return address
+ *	a0 = DST
+ *	a1 = SRC
+ *
+ * On output:
+ *	t8  = bitmask (with one bit set) indicating the last byte written
+ *	a0  = unaligned address of the last *word* written
+ *
+ * Furthermore, v0, a3-a5, t11, and t12 are untouched.
+ */
+
+#include <alpha/regdef.h>
+
+	.set noat
+	.set noreorder
+
+	.text
+
+/* There is a problem with either gdb (as of 4.16) or gas (as of 2.7) that
+   doesn't like putting the entry point for a procedure somewhere in the
+   middle of the procedure descriptor.  Work around this by putting the
+   aligned copy in its own procedure descriptor */
+
+	.ent stxcpy_aligned
+	.align 3
+stxcpy_aligned:
+	.frame sp, 0, t9
+	.prologue 0
+
+	/* On entry to this basic block:
+	   t0 == the first destination word for masking back in
+	   t1 == the first source word.  */
+
+	/* Create the 1st output word and detect 0's in the 1st input word.  */
+	lda	t2, -1		# e1    : build a mask against false zero
+	mskqh	t2, a1, t2	# e0    :   detection in the src word
+	mskqh	t1, a1, t3	# e0    :
+	ornot	t1, t2, t2	# .. e1 :
+	mskql	t0, a1, t0	# e0    : assemble the first output word
+	cmpbge	zero, t2, t7	# .. e1 : bits set iff null found
+	or	t0, t3, t1	# e0    :
+	bne	t7, $a_eos	# .. e1 :
+
+	/* On entry to this basic block:
+	   t0 == the first destination word for masking back in
+	   t1 == a source word not containing a null.  */
+
+$a_loop:
+	stq_u	t1, 0(a0)	# e0    :
+	addq	a0, 8, a0	# .. e1 :
+	ldq_u	t1, 0(a1)	# e0    :
+	addq	a1, 8, a1	# .. e1 :
+	cmpbge	zero, t1, t7	# e0 (stall)
+	beq	t7, $a_loop	# .. e1 (zdb)
+
+	/* Take care of the final (partial) word store.
+	   On entry to this basic block we have:
+	   t1 == the source word containing the null
+	   t7 == the cmpbge mask that found it.  */
+$a_eos:
+	negq	t7, t6		# e0    : find low bit set
+	and	t7, t6, t8	# e1 (stall)
+
+	/* For the sake of the cache, don't read a destination word
+	   if we're not going to need it.  */
+	and	t8, 0x80, t6	# e0    :
+	bne	t6, 1f		# .. e1 (zdb)
+
+	/* We're doing a partial word store and so need to combine
+	   our source and original destination words.  */
+	ldq_u	t0, 0(a0)	# e0    :
+	subq	t8, 1, t6	# .. e1 :
+	zapnot	t1, t6, t1	# e0    : clear src bytes >= null
+	or	t8, t6, t7	# .. e1 :
+	zap	t0, t7, t0	# e0    : clear dst bytes <= null
+	or	t0, t1, t1	# e1    :
+
+1:	stq_u	t1, 0(a0)	# e0    :
+	ret	(t9)		# .. e1 :
+
+	.end stxcpy_aligned
+
+	.align 3
+	.ent __stxcpy
+	.globl __stxcpy
+__stxcpy:
+	.frame sp, 0, t9
+	.prologue 0
+
+	/* Are source and destination co-aligned?  */
+	xor	a0, a1, t0	# e0    :
+	unop			#       :
+	and	t0, 7, t0	# e0    :
+	bne	t0, $unaligned	# .. e1 :
+
+	/* We are co-aligned; take care of a partial first word.  */
+	ldq_u	t1, 0(a1)	# e0    : load first src word
+	and	a0, 7, t0	# .. e1 : take care not to load a word ...
+	addq	a1, 8, a1		# e0    :
+	beq	t0, stxcpy_aligned	# .. e1 : ... if we wont need it
+	ldq_u	t0, 0(a0)	# e0    :
+	br	stxcpy_aligned	# .. e1 :
+
+
+/* The source and destination are not co-aligned.  Align the destination
+   and cope.  We have to be very careful about not reading too much and
+   causing a SEGV.  */
+
+	.align 3
+$u_head:
+	/* We know just enough now to be able to assemble the first
+	   full source word.  We can still find a zero at the end of it
+	   that prevents us from outputting the whole thing.
+
+	   On entry to this basic block:
+	   t0 == the first dest word, for masking back in, if needed else 0
+	   t1 == the low bits of the first source word
+	   t6 == bytemask that is -1 in dest word bytes */
+
+	ldq_u	t2, 8(a1)	# e0    :
+	addq	a1, 8, a1	# .. e1 :
+
+	extql	t1, a1, t1	# e0    :
+	extqh	t2, a1, t4	# e0    :
+	mskql	t0, a0, t0	# e0    :
+	or	t1, t4, t1	# .. e1 :
+	mskqh	t1, a0, t1	# e0    :
+	or	t0, t1, t1	# e1    :
+
+	or	t1, t6, t6	# e0    :
+	cmpbge	zero, t6, t7	# .. e1 :
+	lda	t6, -1		# e0    : for masking just below
+	bne	t7, $u_final	# .. e1 :
+
+	mskql	t6, a1, t6		# e0    : mask out the bits we have
+	or	t6, t2, t2		# e1    :   already extracted before
+	cmpbge	zero, t2, t7		# e0    :   testing eos
+	bne	t7, $u_late_head_exit	# .. e1 (zdb)
+
+	/* Finally, we've got all the stupid leading edge cases taken care
+	   of and we can set up to enter the main loop.  */
+
+	stq_u	t1, 0(a0)	# e0    : store first output word
+	addq	a0, 8, a0	# .. e1 :
+	extql	t2, a1, t0	# e0    : position ho-bits of lo word
+	ldq_u	t2, 8(a1)	# .. e1 : read next high-order source word
+	addq	a1, 8, a1	# e0    :
+	cmpbge	zero, t2, t7	# .. e1 :
+	nop			# e0    :
+	bne	t7, $u_eos	# .. e1 :
+
+	/* Unaligned copy main loop.  In order to avoid reading too much,
+	   the loop is structured to detect zeros in aligned source words.
+	   This has, unfortunately, effectively pulled half of a loop
+	   iteration out into the head and half into the tail, but it does
+	   prevent nastiness from accumulating in the very thing we want
+	   to run as fast as possible.
+
+	   On entry to this basic block:
+	   t0 == the shifted high-order bits from the previous source word
+	   t2 == the unshifted current source word
+
+	   We further know that t2 does not contain a null terminator.  */
+
+	.align 3
+$u_loop:
+	extqh	t2, a1, t1	# e0    : extract high bits for current word
+	addq	a1, 8, a1	# .. e1 :
+	extql	t2, a1, t3	# e0    : extract low bits for next time
+	addq	a0, 8, a0	# .. e1 :
+	or	t0, t1, t1	# e0    : current dst word now complete
+	ldq_u	t2, 0(a1)	# .. e1 : load high word for next time
+	stq_u	t1, -8(a0)	# e0    : save the current word
+	mov	t3, t0		# .. e1 :
+	cmpbge	zero, t2, t7	# e0    : test new word for eos
+	beq	t7, $u_loop	# .. e1 :
+
+	/* We've found a zero somewhere in the source word we just read.
+	   If it resides in the lower half, we have one (probably partial)
+	   word to write out, and if it resides in the upper half, we
+	   have one full and one partial word left to write out.
+
+	   On entry to this basic block:
+	   t0 == the shifted high-order bits from the previous source word
+	   t2 == the unshifted current source word.  */
+$u_eos:
+	extqh	t2, a1, t1	# e0    :
+	or	t0, t1, t1	# e1    : first (partial) source word complete
+
+	cmpbge	zero, t1, t7	# e0    : is the null in this first bit?
+	bne	t7, $u_final	# .. e1 (zdb)
+
+$u_late_head_exit:
+	stq_u	t1, 0(a0)	# e0    : the null was in the high-order bits
+	addq	a0, 8, a0	# .. e1 :
+	extql	t2, a1, t1	# e0    :
+	cmpbge	zero, t1, t7	# .. e1 :
+
+	/* Take care of a final (probably partial) result word.
+	   On entry to this basic block:
+	   t1 == assembled source word
+	   t7 == cmpbge mask that found the null.  */
+$u_final:
+	negq	t7, t6		# e0    : isolate low bit set
+	and	t6, t7, t8	# e1    :
+
+	and	t8, 0x80, t6	# e0    : avoid dest word load if we can
+	bne	t6, 1f		# .. e1 (zdb)
+
+	ldq_u	t0, 0(a0)	# e0    :
+	subq	t8, 1, t6	# .. e1 :
+	or	t6, t8, t7	# e0    :
+	zapnot	t1, t6, t1	# .. e1 : kill source bytes >= null
+	zap	t0, t7, t0	# e0    : kill dest bytes <= null
+	or	t0, t1, t1	# e1    :
+
+1:	stq_u	t1, 0(a0)	# e0    :
+	ret	(t9)		# .. e1 :
+
+	/* Unaligned copy entry point.  */
+	.align 3
+$unaligned:
+
+	ldq_u	t1, 0(a1)	# e0    : load first source word
+
+	and	a0, 7, t4	# .. e1 : find dest misalignment
+	and	a1, 7, t5	# e0    : find src misalignment
+
+	/* Conditionally load the first destination word and a bytemask
+	   with 0xff indicating that the destination byte is sacrosanct.  */
+
+	mov	zero, t0	# .. e1 :
+	mov	zero, t6	# e0    :
+	beq	t4, 1f		# .. e1 :
+	ldq_u	t0, 0(a0)	# e0    :
+	lda	t6, -1		# .. e1 :
+	mskql	t6, a0, t6	# e0    :
+1:
+	subq	a1, t4, a1	# .. e1 : sub dest misalignment from src addr
+
+	/* If source misalignment is larger than dest misalignment, we need
+	   extra startup checks to avoid SEGV.  */
+
+	cmplt	t4, t5, t8	# e0    :
+	beq	t8, $u_head	# .. e1 (zdb)
+
+	lda	t2, -1		# e1    : mask out leading garbage in source
+	mskqh	t2, t5, t2	# e0    :
+	nop			# e0    :
+	ornot	t1, t2, t3	# .. e1 :
+	cmpbge	zero, t3, t7	# e0    : is there a zero?
+	beq	t7, $u_head	# .. e1 (zdb)
+
+	/* At this point we've found a zero in the first partial word of
+	   the source.  We need to isolate the valid source data and mask
+	   it into the original destination data.  (Incidentally, we know
+	   that we'll need at least one byte of that original dest word.) */
+
+	ldq_u	t0, 0(a0)	# e0    :
+
+	negq	t7, t6		# .. e1 : build bitmask of bytes <= zero
+	and	t6, t7, t8	# e0    :
+	and	a1, 7, t5	# .. e1 :
+	subq	t8, 1, t6	# e0    :
+	or	t6, t8, t7	# e1    :
+	srl	t8, t5, t8	# e0    : adjust final null return value
+
+	zapnot	t2, t7, t2	# .. e1 : prepare source word; mirror changes
+	and	t1, t2, t1	# e1    : to source validity mask
+	extql	t2, a1, t2	# .. e0 :
+	extql	t1, a1, t1	# e0    :
+
+	andnot	t0, t2, t0	# .. e1 : zero place for source to reside
+	or	t0, t1, t1	# e1    : and put it there
+	stq_u	t1, 0(a0)	# .. e0 :
+	ret	(t9)		# e1    :
+
+	.end __stxcpy