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Diffstat (limited to 'sysdeps/i386/stpncpy.S')
| -rw-r--r-- | sysdeps/i386/stpncpy.S | 143 |
1 files changed, 143 insertions, 0 deletions
diff --git a/sysdeps/i386/stpncpy.S b/sysdeps/i386/stpncpy.S new file mode 100644 index 0000000000..59192e66c9 --- /dev/null +++ b/sysdeps/i386/stpncpy.S @@ -0,0 +1,143 @@ +/* stpncpy -- copy no more then N bytes from SRC to DEST, returning the + address of the terminating '\0' in DEST. +For Intel 80x86, x>=3. +Copyright (C) 1994, 1995 Free Software Foundation, Inc. +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. +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 Library General Public License as +published by the Free Software Foundation; either version 2 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 +Library General Public License for more details. + +You should have received a copy of the GNU Library General Public +License along with the GNU C Library; see the file COPYING.LIB. If +not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, +Boston, MA 02111-1307, USA. */ + +#include <sysdep.h> +#include "asm-syntax.h" + +/* + INPUT PARAMETERS: + dest (sp + 4) + src (sp + 8) + maxlen (sp + 12) +*/ + + .text +ENTRY (__stpncpy) + + pushl %esi + + movl 8(%esp), %eax /* load destination pointer */ + movl 12(%esp), %esi /* load source pointer */ + movl 16(%esp), %ecx /* load maximal length */ + + subl %eax, %esi /* magic: reduce number of loop variants + to one using addressing mode */ + jmp L1 /* jump to loop "head" */ + + ALIGN(4) + + /* Four times unfolded loop with two loop counters. We get the + the third value (the source address) by using the index+base + adressing mode. */ +L2: movb (%eax,%esi), %dl /* load current char */ + movb %dl, (%eax) /* and store it */ + testb %dl, %dl /* was it NUL? */ + jz L7 /* 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 L6 /* 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 L5 /* 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 L4 /* yes, then exit */ + + addl $4, %eax /* increment loop counter for full round */ + +L1: subl $4, %ecx /* still more than 4 bytes allowed? */ + jae L2 /* 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 L9 /* 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 L3 /* yes, then exit */ + + incl %eax /* increment pointer */ + decl %ecx /* decrement length counter */ + jz L9 /* no more allowed => exit */ + + movb (%eax,%esi), %dl /* load current char */ + movb %dl, (%eax) /* and store it */ + testb %dl, %dl /* was it NUL? */ + jz L3 /* yes, then exit */ + + incl %eax /* increment pointer */ + decl %ecx /* decrement length counter */ + jz L9 /* no more allowed => exit */ + + movb (%eax,%esi), %dl /* load current char */ + movb %dl, (%eax) /* and store it */ + testb %dl, %dl /* was it NUL? */ + jz L3 /* yes, then exit */ + + incl %eax /* increment pointer */ + jmp L9 /* 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. */ +L4: decl %ecx /* decrement counter */ + incl %eax /* increment pointer */ + +L5: decl %ecx /* increment pointer */ + incl %eax /* increment pointer */ + +L6: decl %ecx /* increment pointer */ + incl %eax /* increment pointer */ +L7: + + 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 L9 /* 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 adressing mode + used below is not the same we used above. Here we use the + %ecx register. */ +L8: + movb $0, (%ecx,%eax) /* store NUL char */ +L3: decl %ecx /* all bytes written? */ + jnz L8 /* no, then again */ + +L9: popl %esi /* restore saved register content */ + + ret + +weak_alias (__stpncpy, stpncpy) |