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/* Optimized strncpy/stpncpy implementation for PowerPC64/POWER8.
Copyright (C) 2015-2018 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<>. */
#include <sysdep.h>
# ifndef STPNCPY
# define FUNC_NAME __stpncpy
# else
# endif
# ifndef STRNCPY
# define FUNC_NAME strncpy
# else
# endif
#endif /* !USE_AS_STPNCPY */
#ifndef MEMSET
/* For builds without IFUNC support, local calls should be made to internal
GLIBC symbol (created by libc_hidden_builtin_def). */
# ifdef SHARED
# define MEMSET_is_local
# define MEMSET __GI_memset
# else
# define MEMSET memset
# endif
/* Implements the function
char * [r3] strncpy (char *dest [r3], const char *src [r4], size_t n [r5])
char * [r3] stpncpy (char *dest [r3], const char *src [r4], size_t n [r5])
if USE_AS_STPCPY is defined.
The implementation uses unaligned doubleword access to avoid specialized
code paths depending of data alignment. Although recent powerpc64 uses
64K as default, the page cross handling assumes minimum page size of
4k. */
.machine power7
#ifdef MEMSET_is_local
/* Check if the [src]+15 will cross a 4K page by checking if the bit
indicating the page size changes. Basically:
uint64_t srcin = (uint64_t)src;
uint64_t ob = srcin & 4096UL;
uint64_t nb = (srcin+15UL) & 4096UL;
if (ob ^ nb)
goto pagecross; */
addi r10,r4,16
rlwinm r9,r4,0,19,19
/* Save some non-volatile registers on the stack. */
std r26,-48(r1)
std r27,-40(r1)
rlwinm r8,r10,0,19,19
std r28,-32(r1)
std r29,-24(r1)
cmpld cr7,r9,r8
std r30,-16(r1)
std r31,-8(r1)
/* Update CFI. */
cfi_offset(r26, -48)
cfi_offset(r27, -40)
cfi_offset(r28, -32)
cfi_offset(r29, -24)
cfi_offset(r30, -16)
cfi_offset(r31, -8)
beq cr7,L(unaligned_lt_16)
rldicl r9,r4,0,61
subfic r8,r9,8
cmpld cr7,r5,r8
bgt cr7,L(pagecross)
/* At this points there is 1 to 15 bytes to check and write. Since it could
be either from first unaligned 16 bytes access or from bulk copy, the code
uses an unrolled byte read/write instead of trying to analyze the cmpb
results. */
mr r9,r3
/* Return if there are no more bytes to be written. */
cmpdi cr7,r5,0
beq cr7,L(short_path_loop_end_1)
/* Copy one char from src (r4) and write it to dest (r9). If it is the
end-of-string, start the null padding. Continue, otherwise. */
lbz r10,0(r4)
cmpdi cr7,r10,0
stb r10,0(r9)
beq cr7,L(zero_pad_start_1)
/* If there are no more bytes to be written, return. */
cmpdi cr0,r5,1
addi r8,r9,1
addi r6,r5,-1
beq cr0,L(short_path_loop_end_0)
/* Copy another char from src (r4) to dest (r9). Check again if it is
the end-of-string. If so, start the null padding. */
lbz r10,1(r4)
cmpdi cr7,r10,0
stb r10,1(r9)
beq cr7,L(zero_pad_start_prepare_1)
/* Eagerly decrement r5 by 3, which is the number of bytes already
written, plus one write that will be performed later on. */
addi r10,r5,-3
b L(short_path_loop_1)
.align 4
/* At this point, the induction variable, r5, as well as the pointers
to dest and src (r9 and r4, respectivelly) have been updated.
Note: The registers r7 and r10 are induction variables derived from
r5. They are used to determine if the total number of writes has
been reached at every other write.
Copy one char from src (r4) and write it to dest (r9). If it is the
end-of-string, start the null padding. Continue, otherwise. */
lbz r8,0(r4)
addi r7,r10,-2
cmpdi cr5,r8,0
stb r8,0(r9)
beq cr5,L(zero_pad_start_1)
beq cr7,L(short_path_loop_end_0)
/* Copy another char from src (r4) to dest (r9). Check again if it is
the end-of-string. If so, start the null padding. */
lbz r8,1(r4)
cmpdi cr7,r8,0
stb r8,1(r9)
beq cr7,L(zero_pad_start)
mr r10,r7
/* This block is reached after two chars have been already written to
dest. Nevertheless, r5 (the induction variable), r9 (the pointer to
dest), and r4 (the pointer to src) have not yet been updated.
At this point:
r5 holds the count of bytes yet to be written plus 2.
r9 points to the last two chars that were already written to dest.
r4 points to the last two chars that were already copied from src.
The algorithm continues by decrementing r5, the induction variable,
so that it reflects the last two writes. The pointers to dest (r9)
and to src (r4) are increment by two, for the same reason.
Note: Register r10 is another induction variable, derived from r5,
which determines if the total number of writes has been reached. */
addic. r5,r5,-2
addi r9,r9,2
cmpdi cr7,r10,0 /* Eagerly check if the next write is the last. */
addi r4,r4,2
addi r6,r9,1
bne cr0,L(short_path_loop) /* Check if the total number of writes
has been reached at every other
write. */
mr r3,r9
b L(short_path_loop_end)
addi r3,r9,1
b L(short_path_loop_end)
mr r3,r9
/* Restore non-volatile registers. */
ld r26,-48(r1)
ld r27,-40(r1)
ld r28,-32(r1)
ld r29,-24(r1)
ld r30,-16(r1)
ld r31,-8(r1)
/* This code pads the remainder of dest with NULL bytes. The algorithm
calculates the remaining size and calls memset. */
.align 4
mr r5,r10
mr r9,r6
/* At this point:
- r5 holds the number of bytes that still have to be written to
- r9 points to the position, in dest, where the first null byte
will be written.
The above statements are true both when control reaches this label
from a branch or when falling through the previous lines. */
mr r30,r3 /* Save the return value of strncpy. */
/* Prepare the call to memset. */
mr r3,r9 /* Pointer to the area to be zero-filled. */
li r4,0 /* Byte to be written (zero). */
/* We delayed the creation of the stack frame, as well as the saving of
the link register, because only at this point, we are sure that
doing so is actually needed. */
/* Save the link register. */
mflr r0
std r0,16(r1)
/* Create the stack frame. */
stdu r1,-FRAMESIZE(r1)
cfi_offset(lr, 16)
#ifndef MEMSET_is_local
ld r0,FRAMESIZE+16(r1)
mr r3,r30 /* Restore the return value of strncpy, i.e.:
dest. For stpncpy, the return value is the
same as return value of memset. */
/* Restore non-volatile registers and return. */
ld r26,FRAMESIZE-48(r1)
ld r27,FRAMESIZE-40(r1)
ld r28,FRAMESIZE-32(r1)
ld r29,FRAMESIZE-24(r1)
ld r30,FRAMESIZE-16(r1)
ld r31,FRAMESIZE-8(r1)
/* Restore the stack frame. */
addi r1,r1,FRAMESIZE
/* Restore the link register. */
mtlr r0
/* The common case where [src]+16 will not cross a 4K page boundary.
In this case the code fast check the first 16 bytes by using doubleword
read/compares and update destiny if neither total size or null byte
is found in destiny. */
.align 4
cmpldi cr7,r5,7
ble cr7,L(short_path)
ld r7,0(r4)
li r8,0
cmpb r8,r7,r8
cmpdi cr7,r8,0
bne cr7,L(short_path_prepare_2)
addi r6,r5,-8
std r7,0(r3)
addi r9,r3,8
cmpldi cr7,r6,7
addi r7,r4,8
ble cr7,L(short_path_prepare_1_1)
ld r4,8(r4)
cmpb r8,r4,r8
cmpdi cr7,r8,0
bne cr7,L(short_path_prepare_2_1)
std r4,8(r3)
addi r29,r3,16
addi r5,r5,-16
/* Neither the null byte was found or total length was reached,
align to 16 bytes and issue a bulk copy/compare. */
b L(align_to_16b)
/* In the case of 4k page boundary cross, the algorithm first align
the address to a doubleword, calculate a mask based on alignment
to ignore the bytes and continue using doubleword. */
.align 4
rldicr r11,r4,0,59 /* Align the address to 8 bytes boundary. */
li r6,-1 /* MASK = 0xffffffffffffffffUL. */
sldi r9,r9,3 /* Calculate padding. */
ld r7,0(r11) /* Load doubleword from memory. */
#ifdef __LITTLE_ENDIAN__
sld r9,r6,r9 /* MASK = MASK << padding. */
srd r9,r6,r9 /* MASK = MASK >> padding. */
orc r9,r7,r9 /* Mask bits that are not part of the
string. */
li r7,0
cmpb r9,r9,r7 /* Check for null bytes in DWORD1. */
cmpdi cr7,r9,0
bne cr7,L(short_path_prepare_2)
subf r8,r8,r5 /* Adjust total length. */
cmpldi cr7,r8,8 /* Check if length was reached. */
ble cr7,L(short_path_prepare_2)
/* For next checks we have aligned address, so we check for more
three doublewords to make sure we can read 16 unaligned bytes
to start the bulk copy with 16 aligned addresses. */
ld r7,8(r11)
cmpb r9,r7,r9
cmpdi cr7,r9,0
bne cr7,L(short_path_prepare_2)
addi r7,r8,-8
cmpldi cr7,r7,8
ble cr7,L(short_path_prepare_2)
ld r7,16(r11)
cmpb r9,r7,r9
cmpdi cr7,r9,0
bne cr7,L(short_path_prepare_2)
addi r8,r8,-16
cmpldi cr7,r8,8
ble cr7,L(short_path_prepare_2)
ld r8,24(r11)
cmpb r9,r8,r9
cmpdi cr7,r9,0
bne cr7,L(short_path_prepare_2)
/* No null byte found in the 32 bytes readed and length not reached,
read source again using unaligned loads and store them. */
ld r9,0(r4)
addi r29,r3,16
addi r5,r5,-16
std r9,0(r3)
ld r9,8(r4)
std r9,8(r3)
/* Align source to 16 bytes and adjust destiny and size. */
rldicl r9,r10,0,60
rldicr r28,r10,0,59
add r12,r5,r9
subf r29,r9,r29
/* The bulk read/compare/copy loads two doublewords, compare and merge
in a single register for speed. This is an attempt to speed up the
null-checking process for bigger strings. */
cmpldi cr7,r12,15
ble cr7,L(short_path_prepare_1_2)
/* Main loop for large sizes, unrolled 2 times to get better use of
pipeline. */
ld r8,0(28)
ld r10,8(28)
li r9,0
cmpb r7,r8,r9
cmpb r9,r10,r9
or. r6,r9,r7
bne cr0,L(short_path_prepare_2_3)
addi r5,r12,-16
addi r4,r28,16
std r8,0(r29)
std r10,8(r29)
cmpldi cr7,r5,15
addi r9,r29,16
ble cr7,L(short_path_1)
mr r11,r28
mr r6,r29
li r30,0
subfic r26,r4,48
subfic r27,r9,48
b L(loop_16b)
.align 4
ld r31,0(r11)
ld r10,8(r11)
cmpb r0,r31,r7
cmpb r8,r10,r7
or. r7,r0,r8
addi r5,r5,-32
cmpldi cr7,r5,15
add r4,r4,r26
add r9,r9,r27
bne cr0,L(short_path_prepare_2_2)
add r4,r28,r4
std r31,0(r6)
add r9,r29,r9
std r10,8(r6)
ble cr7,L(short_path_1)
ld r10,16(r11)
ld r0,24(r11)
cmpb r8,r10,r30
cmpb r7,r0,r30
or. r7,r8,r7
addi r12,r12,-32
cmpldi cr7,r12,15
addi r11,r11,32
bne cr0,L(short_path_2)
std r10,16(r6)
addi r6,r6,32
std r0,-8(r6)
bgt cr7,L(loop_start)
mr r5,r12
mr r4,r11
mr r9,r6
b L(short_path_1)
.align 4
mr r5,r6
mr r4,r7
b L(short_path_1)
mr r5,r12
mr r4,r28
mr r9,r29
b L(short_path_1)
mr r9,r3
b L(short_path_2)
mr r5,r6
mr r4,r7
b L(short_path_2)
mr r5,r12
mr r4,r11
mr r9,r6
b L(short_path_2)
mr r5,r12
mr r4,r28
mr r9,r29
b L(short_path_2)
mr r5,r6
mr r9,r8
b L(zero_pad_start_1)
libc_hidden_builtin_def (strncpy)