/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* arch/alpha/lib/stxncpy.S
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* Contributed by Richard Henderson (rth@tamu.edu)
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*
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* Copy no more than COUNT bytes of the null-terminated string from
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* SRC to DST.
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*
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* This is an internal routine used by strncpy, stpncpy, and strncat.
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* As such, it uses special linkage conventions to make implementation
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* of these public functions more efficient.
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*
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* On input:
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* t9 = return address
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* a0 = DST
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* a1 = SRC
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* a2 = COUNT
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*
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* Furthermore, COUNT may not be zero.
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*
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* On output:
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* t0 = last word written
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* t10 = bitmask (with one bit set) indicating the byte position of
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* the end of the range specified by COUNT
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* t12 = bitmask (with one bit set) indicating the last byte written
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* a0 = unaligned address of the last *word* written
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* a2 = the number of full words left in COUNT
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*
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* Furthermore, v0, a3-a5, t11, and $at are untouched.
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*/
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#include <asm/regdef.h>
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.set noat
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.set noreorder
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.text
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/* There is a problem with either gdb (as of 4.16) or gas (as of 2.7) that
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doesn't like putting the entry point for a procedure somewhere in the
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middle of the procedure descriptor. Work around this by putting the
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aligned copy in its own procedure descriptor */
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.ent stxncpy_aligned
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.align 3
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stxncpy_aligned:
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.frame sp, 0, t9, 0
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.prologue 0
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/* On entry to this basic block:
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t0 == the first destination word for masking back in
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t1 == the first source word. */
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/* Create the 1st output word and detect 0's in the 1st input word. */
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lda t2, -1 # e1 : build a mask against false zero
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mskqh t2, a1, t2 # e0 : detection in the src word
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mskqh t1, a1, t3 # e0 :
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ornot t1, t2, t2 # .. e1 :
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mskql t0, a1, t0 # e0 : assemble the first output word
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cmpbge zero, t2, t8 # .. e1 : bits set iff null found
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or t0, t3, t0 # e0 :
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beq a2, $a_eoc # .. e1 :
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bne t8, $a_eos # .. e1 :
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/* On entry to this basic block:
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t0 == a source word not containing a null. */
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$a_loop:
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stq_u t0, 0(a0) # e0 :
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addq a0, 8, a0 # .. e1 :
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ldq_u t0, 0(a1) # e0 :
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addq a1, 8, a1 # .. e1 :
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subq a2, 1, a2 # e0 :
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cmpbge zero, t0, t8 # .. e1 (stall)
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beq a2, $a_eoc # e1 :
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beq t8, $a_loop # e1 :
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/* Take care of the final (partial) word store. At this point
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the end-of-count bit is set in t8 iff it applies.
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On entry to this basic block we have:
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t0 == the source word containing the null
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t8 == the cmpbge mask that found it. */
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$a_eos:
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negq t8, t12 # e0 : find low bit set
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and t8, t12, t12 # e1 (stall)
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/* For the sake of the cache, don't read a destination word
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if we're not going to need it. */
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and t12, 0x80, t6 # e0 :
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bne t6, 1f # .. e1 (zdb)
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/* We're doing a partial word store and so need to combine
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our source and original destination words. */
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ldq_u t1, 0(a0) # e0 :
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subq t12, 1, t6 # .. e1 :
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or t12, t6, t8 # e0 :
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unop #
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zapnot t0, t8, t0 # e0 : clear src bytes > null
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zap t1, t8, t1 # .. e1 : clear dst bytes <= null
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or t0, t1, t0 # e1 :
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1: stq_u t0, 0(a0) # e0 :
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ret (t9) # e1 :
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/* Add the end-of-count bit to the eos detection bitmask. */
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$a_eoc:
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or t10, t8, t8
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br $a_eos
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.end stxncpy_aligned
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.align 3
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.ent __stxncpy
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.globl __stxncpy
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__stxncpy:
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.frame sp, 0, t9, 0
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.prologue 0
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/* Are source and destination co-aligned? */
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xor a0, a1, t1 # e0 :
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and a0, 7, t0 # .. e1 : find dest misalignment
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and t1, 7, t1 # e0 :
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addq a2, t0, a2 # .. e1 : bias count by dest misalignment
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subq a2, 1, a2 # e0 :
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and a2, 7, t2 # e1 :
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srl a2, 3, a2 # e0 : a2 = loop counter = (count - 1)/8
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addq zero, 1, t10 # .. e1 :
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sll t10, t2, t10 # e0 : t10 = bitmask of last count byte
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bne t1, $unaligned # .. e1 :
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/* We are co-aligned; take care of a partial first word. */
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ldq_u t1, 0(a1) # e0 : load first src word
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addq a1, 8, a1 # .. e1 :
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beq t0, stxncpy_aligned # avoid loading dest word if not needed
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ldq_u t0, 0(a0) # e0 :
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br stxncpy_aligned # .. e1 :
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/* The source and destination are not co-aligned. Align the destination
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and cope. We have to be very careful about not reading too much and
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causing a SEGV. */
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.align 3
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$u_head:
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/* We know just enough now to be able to assemble the first
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full source word. We can still find a zero at the end of it
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that prevents us from outputting the whole thing.
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On entry to this basic block:
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t0 == the first dest word, unmasked
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t1 == the shifted low bits of the first source word
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t6 == bytemask that is -1 in dest word bytes */
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ldq_u t2, 8(a1) # e0 : load second src word
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addq a1, 8, a1 # .. e1 :
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mskql t0, a0, t0 # e0 : mask trailing garbage in dst
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extqh t2, a1, t4 # e0 :
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or t1, t4, t1 # e1 : first aligned src word complete
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mskqh t1, a0, t1 # e0 : mask leading garbage in src
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or t0, t1, t0 # e0 : first output word complete
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or t0, t6, t6 # e1 : mask original data for zero test
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cmpbge zero, t6, t8 # e0 :
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beq a2, $u_eocfin # .. e1 :
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lda t6, -1 # e0 :
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bne t8, $u_final # .. e1 :
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mskql t6, a1, t6 # e0 : mask out bits already seen
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nop # .. e1 :
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stq_u t0, 0(a0) # e0 : store first output word
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or t6, t2, t2 # .. e1 :
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cmpbge zero, t2, t8 # e0 : find nulls in second partial
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addq a0, 8, a0 # .. e1 :
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subq a2, 1, a2 # e0 :
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bne t8, $u_late_head_exit # .. e1 :
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/* Finally, we've got all the stupid leading edge cases taken care
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of and we can set up to enter the main loop. */
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extql t2, a1, t1 # e0 : position hi-bits of lo word
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beq a2, $u_eoc # .. e1 :
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ldq_u t2, 8(a1) # e0 : read next high-order source word
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addq a1, 8, a1 # .. e1 :
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extqh t2, a1, t0 # e0 : position lo-bits of hi word (stall)
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cmpbge zero, t2, t8 # .. e1 :
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nop # e0 :
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bne t8, $u_eos # .. e1 :
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/* Unaligned copy main loop. In order to avoid reading too much,
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the loop is structured to detect zeros in aligned source words.
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This has, unfortunately, effectively pulled half of a loop
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iteration out into the head and half into the tail, but it does
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prevent nastiness from accumulating in the very thing we want
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to run as fast as possible.
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On entry to this basic block:
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t0 == the shifted low-order bits from the current source word
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t1 == the shifted high-order bits from the previous source word
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t2 == the unshifted current source word
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We further know that t2 does not contain a null terminator. */
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.align 3
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$u_loop:
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or t0, t1, t0 # e0 : current dst word now complete
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subq a2, 1, a2 # .. e1 : decrement word count
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stq_u t0, 0(a0) # e0 : save the current word
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addq a0, 8, a0 # .. e1 :
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extql t2, a1, t1 # e0 : extract high bits for next time
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beq a2, $u_eoc # .. e1 :
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ldq_u t2, 8(a1) # e0 : load high word for next time
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addq a1, 8, a1 # .. e1 :
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nop # e0 :
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cmpbge zero, t2, t8 # e1 : test new word for eos (stall)
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extqh t2, a1, t0 # e0 : extract low bits for current word
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beq t8, $u_loop # .. e1 :
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/* We've found a zero somewhere in the source word we just read.
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If it resides in the lower half, we have one (probably partial)
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word to write out, and if it resides in the upper half, we
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have one full and one partial word left to write out.
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On entry to this basic block:
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t0 == the shifted low-order bits from the current source word
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t1 == the shifted high-order bits from the previous source word
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t2 == the unshifted current source word. */
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$u_eos:
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or t0, t1, t0 # e0 : first (partial) source word complete
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nop # .. e1 :
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cmpbge zero, t0, t8 # e0 : is the null in this first bit?
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bne t8, $u_final # .. e1 (zdb)
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stq_u t0, 0(a0) # e0 : the null was in the high-order bits
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addq a0, 8, a0 # .. e1 :
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subq a2, 1, a2 # e1 :
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$u_late_head_exit:
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extql t2, a1, t0 # .. e0 :
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cmpbge zero, t0, t8 # e0 :
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or t8, t10, t6 # e1 :
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cmoveq a2, t6, t8 # e0 :
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nop # .. e1 :
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/* Take care of a final (probably partial) result word.
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On entry to this basic block:
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t0 == assembled source word
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t8 == cmpbge mask that found the null. */
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$u_final:
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negq t8, t6 # e0 : isolate low bit set
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and t6, t8, t12 # e1 :
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and t12, 0x80, t6 # e0 : avoid dest word load if we can
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bne t6, 1f # .. e1 (zdb)
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ldq_u t1, 0(a0) # e0 :
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subq t12, 1, t6 # .. e1 :
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or t6, t12, t8 # e0 :
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zapnot t0, t8, t0 # .. e1 : kill source bytes > null
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zap t1, t8, t1 # e0 : kill dest bytes <= null
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or t0, t1, t0 # e1 :
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1: stq_u t0, 0(a0) # e0 :
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ret (t9) # .. e1 :
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/* Got to end-of-count before end of string.
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On entry to this basic block:
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t1 == the shifted high-order bits from the previous source word */
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$u_eoc:
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and a1, 7, t6 # e1 :
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sll t10, t6, t6 # e0 :
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and t6, 0xff, t6 # e0 :
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bne t6, 1f # .. e1 :
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ldq_u t2, 8(a1) # e0 : load final src word
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nop # .. e1 :
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extqh t2, a1, t0 # e0 : extract low bits for last word
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or t1, t0, t1 # e1 :
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1: cmpbge zero, t1, t8
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mov t1, t0
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$u_eocfin: # end-of-count, final word
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or t10, t8, t8
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br $u_final
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/* Unaligned copy entry point. */
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.align 3
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$unaligned:
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ldq_u t1, 0(a1) # e0 : load first source word
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and a0, 7, t4 # .. e1 : find dest misalignment
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and a1, 7, t5 # e0 : find src misalignment
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/* Conditionally load the first destination word and a bytemask
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with 0xff indicating that the destination byte is sacrosanct. */
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mov zero, t0 # .. e1 :
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mov zero, t6 # e0 :
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beq t4, 1f # .. e1 :
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ldq_u t0, 0(a0) # e0 :
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lda t6, -1 # .. e1 :
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mskql t6, a0, t6 # e0 :
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subq a1, t4, a1 # .. e1 : sub dest misalignment from src addr
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/* If source misalignment is larger than dest misalignment, we need
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extra startup checks to avoid SEGV. */
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1: cmplt t4, t5, t12 # e1 :
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extql t1, a1, t1 # .. e0 : shift src into place
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lda t2, -1 # e0 : for creating masks later
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beq t12, $u_head # .. e1 :
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extql t2, a1, t2 # e0 :
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cmpbge zero, t1, t8 # .. e1 : is there a zero?
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andnot t2, t6, t2 # e0 : dest mask for a single word copy
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or t8, t10, t5 # .. e1 : test for end-of-count too
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cmpbge zero, t2, t3 # e0 :
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cmoveq a2, t5, t8 # .. e1 :
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andnot t8, t3, t8 # e0 :
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beq t8, $u_head # .. e1 (zdb)
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/* At this point we've found a zero in the first partial word of
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the source. We need to isolate the valid source data and mask
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it into the original destination data. (Incidentally, we know
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that we'll need at least one byte of that original dest word.) */
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ldq_u t0, 0(a0) # e0 :
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negq t8, t6 # .. e1 : build bitmask of bytes <= zero
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mskqh t1, t4, t1 # e0 :
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and t6, t8, t12 # .. e1 :
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subq t12, 1, t6 # e0 :
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or t6, t12, t8 # e1 :
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zapnot t2, t8, t2 # e0 : prepare source word; mirror changes
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zapnot t1, t8, t1 # .. e1 : to source validity mask
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andnot t0, t2, t0 # e0 : zero place for source to reside
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or t0, t1, t0 # e1 : and put it there
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stq_u t0, 0(a0) # e0 :
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ret (t9) # .. e1 :
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.end __stxncpy
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