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.file "strncat.S"
.section .text
.global _strncat
.type _strncat,@function
_strncat:
;; On entry: r1 => Destination
;; r2 => Source
;; r3 => Max number of bytes to copy
mov r1, r4 ; Save a copy of the dest pointer.
mov r2, r5 ; Save a copy of the source pointer.
mov r3, r14 ; Save a copy of the byte count.
mov #0, r2 ; Search for the NUL byte.
mov #-1, r3 ; Search until we run out of memory.
suntil.b ; Find the end of the destination string.
sub #1, r1 ; suntil.b leaves r1 pointing to the byte beyond the NUL.
mov r14, r3 ; Restore the limit on the number of bytes copied.
mov r5, r2 ; Restore the source pointer.
mov r1, r5 ; Save a copy of the dest pointer.
smovu ; Copy source to destination.
add #0, r14, r3 ; Restore the number of bytes to copy (again), but this time set the Z flag as well.
beq 1f ; If we copied 0 bytes then we already know that the dest string is NUL terminated, so we do not have to do anything.
mov #0, r2 ; Otherwise we must check to see if a NUL byte
mov r5, r1 ; was included in the bytes that were copied.
suntil.b
beq 1f ; Z flag is set if a match was found.
add r14, r5 ; Point at byte after end of copied bytes.
mov.b #0, [r5] ; Store a NUL there.
1:
mov r4, r1 ; Return the original dest pointer.
rts
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