diff options
Diffstat (limited to 'REORG.TODO/sysdeps/i386/stpncpy.S')
| -rw-r--r-- | REORG.TODO/sysdeps/i386/stpncpy.S | 147 |
1 files changed, 147 insertions, 0 deletions
diff --git a/REORG.TODO/sysdeps/i386/stpncpy.S b/REORG.TODO/sysdeps/i386/stpncpy.S new file mode 100644 index 0000000000..46f2aba713 --- /dev/null +++ b/REORG.TODO/sysdeps/i386/stpncpy.S @@ -0,0 +1,147 @@ +/* copy no more than N bytes from SRC to DEST, returning the address of + the terminating '\0' in DEST. + For Intel 80x86, x>=3. + Copyright (C) 1994-2017 Free Software Foundation, Inc. + This file is part of the GNU C Library. + Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu> + Some bug fixes by Alan Modra <Alan@SPRI.Levels.UniSA.Edu.Au> + - original wrote n+1 chars in some cases. + - stpncpy() ought to behave like strncpy() ie. not null-terminate + if limited by n. glibc-1.09 stpncpy() does this. + + 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 + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + 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 + <http://www.gnu.org/licenses/>. */ + +#include <sysdep.h> +#include "asm-syntax.h" + +#define PARMS 4+4 /* space for 1 saved reg */ +#define RTN PARMS +#define DEST RTN +#define SRC DEST+4 +#define LEN SRC+4 + + .text +ENTRY (__stpncpy) + + pushl %esi + cfi_adjust_cfa_offset (4) + + movl DEST(%esp), %eax + movl SRC(%esp), %esi + cfi_rel_offset (esi, 0) + movl LEN(%esp), %ecx + + subl %eax, %esi /* magic: reduce number of loop variants + to one using addressing mode */ + jmp L(1) /* jump to loop "head" */ + + ALIGN(4) + + /* Four times unfolded loop with two loop counters. We get the + third value (the source address) by using the index+base + addressing mode. */ +L(2): movb (%eax,%esi), %dl /* load current char */ + movb %dl, (%eax) /* and store it */ + testb %dl, %dl /* was it NUL? */ + jz L(7) /* yes, then exit */ + + movb 1(%eax,%esi), %dl /* load current char */ + movb %dl, 1(%eax) /* and store it */ + testb %dl, %dl /* was it NUL? */ + jz L(6) /* yes, then exit */ + + movb 2(%eax,%esi), %dl /* load current char */ + movb %dl, 2(%eax) /* and store it */ + testb %dl, %dl /* was it NUL? */ + jz L(5) /* yes, then exit */ + + movb 3(%eax,%esi), %dl /* load current char */ + movb %dl, 3(%eax) /* and store it */ + testb %dl, %dl /* was it NUL? */ + jz L(4) /* yes, then exit */ + + addl $4, %eax /* increment loop counter for full round */ + +L(1): subl $4, %ecx /* still more than 4 bytes allowed? */ + jae L(2) /* yes, then go to start of loop */ + + /* The maximal remaining 15 bytes are not processed in a loop. */ + + addl $4, %ecx /* correct above subtraction */ + jz L(9) /* maximal allowed char reached => go to end */ + + movb (%eax,%esi), %dl /* load current char */ + movb %dl, (%eax) /* and store it */ + testb %dl, %dl /* was it NUL? */ + jz L(3) /* yes, then exit */ + + incl %eax /* increment pointer */ + decl %ecx /* decrement length counter */ + jz L(9) /* no more allowed => exit */ + + movb (%eax,%esi), %dl /* load current char */ + movb %dl, (%eax) /* and store it */ + testb %dl, %dl /* was it NUL? */ + jz L(3) /* yes, then exit */ + + incl %eax /* increment pointer */ + decl %ecx /* decrement length counter */ + jz L(9) /* no more allowed => exit */ + + movb (%eax,%esi), %dl /* load current char */ + movb %dl, (%eax) /* and store it */ + testb %dl, %dl /* was it NUL? */ + jz L(3) /* yes, then exit */ + + incl %eax /* increment pointer */ + jmp L(9) /* we don't have to test for counter underflow + because we know we had a most 3 bytes + remaining => exit */ + + /* When coming from the main loop we have to adjust the pointer. */ +L(4): decl %ecx /* decrement counter */ + incl %eax /* increment pointer */ + +L(5): decl %ecx /* increment pointer */ + incl %eax /* increment pointer */ + +L(6): decl %ecx /* increment pointer */ + incl %eax /* increment pointer */ +L(7): + + addl $3, %ecx /* correct pre-decrementation of counter + at the beginning of the loop; but why 3 + and not 4? Very simple, we have to count + the NUL char we already wrote. */ + jz L(9) /* counter is also 0 => exit */ + + /* We now have to fill the rest of the buffer with NUL. This + is done in a tricky way. Please note that the addressing mode + used below is not the same we used above. Here we use the + %ecx register. */ +L(8): + movb $0, (%ecx,%eax) /* store NUL char */ +L(3): decl %ecx /* all bytes written? */ + jnz L(8) /* no, then again */ + +L(9): popl %esi /* restore saved register content */ + cfi_adjust_cfa_offset (-4) + cfi_restore (esi) + + ret +END (__stpncpy) + +libc_hidden_def (__stpncpy) +weak_alias (__stpncpy, stpncpy) |