| /* 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) 1994-2016 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) |