alpha/lib/strncpy.S

0001 /* SPDX-License-Identifier: GPL-2.0 */
0002 /*
0003  * arch/alpha/lib/strncpy.S
0004  * Contributed by Richard Henderson (rth@tamu.edu)
0005  *
0006  * Copy no more than COUNT bytes of the null-terminated string from
0007  * SRC to DST.  If SRC does not cover all of COUNT, the balance is
0008  * zeroed.
0009  *
0010  * Or, rather, if the kernel cared about that weird ANSI quirk.  This
0011  * version has cropped that bit o' nastiness as well as assuming that
0012  * __stxncpy is in range of a branch.
0013  */
0014 #include <asm/export.h>
0015     .set noat
0016     .set noreorder
0017
0018     .text
0019
0020     .align 4
0021     .globl strncpy
0022     .ent strncpy
0023 strncpy:
0024     .frame $30, 0, $26
0025     .prologue 0
0026
0027     mov $16, $0     # set return value now
0028     beq $18, $zerolen
0029     unop
0030     bsr $23, __stxncpy  # do the work of the copy
0031
0032     unop
0033     bne $18, $multiword # do we have full words left?
0034     subq    $24, 1, $3  # nope
0035     subq    $27, 1, $4
0036
0037     or  $3, $24, $3 # clear the bits between the last
0038     or  $4, $27, $4 # written byte and the last byte in COUNT
0039     andnot  $3, $4, $4
0040     zap $1, $4, $1
0041
0042     stq_u   $1, 0($16)
0043     ret
0044
0045     .align  4
0046 $multiword:
0047     subq    $27, 1, $2  # clear the final bits in the prev word
0048     or  $2, $27, $2
0049     zapnot  $1, $2, $1
0050     subq    $18, 1, $18
0051
0052     stq_u   $1, 0($16)
0053     addq    $16, 8, $16
0054     unop
0055     beq $18, 1f
0056
0057     nop
0058     unop
0059     nop
0060     blbc    $18, 0f
0061
0062     stq_u   $31, 0($16) # zero one word
0063     subq    $18, 1, $18
0064     addq    $16, 8, $16
0065     beq $18, 1f
0066
0067 0:  stq_u   $31, 0($16) # zero two words
0068     subq    $18, 2, $18
0069     stq_u   $31, 8($16)
0070     addq    $16, 16, $16
0071     bne $18, 0b
0072
0073 1:  ldq_u   $1, 0($16)  # clear the leading bits in the final word
0074     subq    $24, 1, $2
0075     or  $2, $24, $2
0076
0077     zap $1, $2, $1
0078     stq_u   $1, 0($16)
0079 $zerolen:
0080     ret
0081
0082     .end    strncpy
0083     EXPORT_SYMBOL(strncpy)