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36 lines
1.3 KiB
ArmAsm
36 lines
1.3 KiB
ArmAsm
.file "strncat.S"
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.section .text
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.global _strncat
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.type _strncat,@function
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_strncat:
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;; On entry: r1 => Destination
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;; r2 => Source
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;; r3 => Max number of bytes to copy
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mov r1, r4 ; Save a copy of the dest pointer.
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mov r2, r5 ; Save a copy of the source pointer.
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mov r3, r14 ; Save a copy of the byte count.
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mov #0, r2 ; Search for the NUL byte.
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mov #-1, r3 ; Search until we run out of memory.
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suntil.b ; Find the end of the destination string.
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sub #1, r1 ; suntil.b leaves r1 pointing to the byte beyond the NUL.
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mov r14, r3 ; Restore the limit on the number of bytes copied.
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mov r5, r2 ; Restore the source pointer.
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mov r1, r5 ; Save a copy of the dest pointer.
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smovu ; Copy source to destination.
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add #0, r14, r3 ; Restore the number of bytes to copy (again), but this time set the Z flag as well.
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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.
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mov #0, r2 ; Otherwise we must check to see if a NUL byte
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mov r5, r1 ; was included in the bytes that were copied.
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suntil.b
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beq 1f ; Z flag is set if a match was found.
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add r14, r5 ; Point at byte after end of copied bytes.
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mov.b #0, [r5] ; Store a NUL there.
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1:
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mov r4, r1 ; Return the original dest pointer.
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rts
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