diff options
Diffstat (limited to 'sysdeps/i386/strchrnul.S')
| -rw-r--r-- | sysdeps/i386/strchrnul.S | 53 |
1 files changed, 28 insertions, 25 deletions
diff --git a/sysdeps/i386/strchrnul.S b/sysdeps/i386/strchrnul.S index f42a697..6860a11 100644 --- a/sysdeps/i386/strchrnul.S +++ b/sysdeps/i386/strchrnul.S @@ -1,7 +1,7 @@ -/* strchrnul (str, ch) -- Return pointer to first occurrence of CH in STR +/* strchrnul (str, chr) -- Return pointer to first occurrence of CHR in STR or the final NUL byte. For Intel 80x86, x>=3. - Copyright (C) 1994, 1995, 1996, 1997, 1999 Free Software Foundation, Inc. + Copyright (C) 1994, 1995, 1996, 1997, 1999, 2000 Free Software Foundation, Inc. This file is part of the GNU C Library. Contributed by Ulrich Drepper <drepper@gnu.org> Some optimisations by Alan Modra <Alan@SPRI.Levels.UniSA.Edu.Au> @@ -23,22 +23,24 @@ #include <sysdep.h> #include "asm-syntax.h" +#include "bp-asm.h" -/* - INPUT PARAMETERS: - str (sp + 4) - ch (sp + 8) -*/ +#define PARMS LINKAGE+4 /* space for 1 saved reg */ +#define RTN PARMS +#define STR RTN+RTN_SIZE +#define CHR STR+PTR_SIZE .text ENTRY (__strchrnul) + ENTER + pushl %edi /* Save callee-safe registers used here. */ - movl 8(%esp), %eax /* get string pointer */ - movl 12(%esp), %edx /* get character we are looking for */ + movl STR(%esp), %eax + movl CHR(%esp), %edx - /* At the moment %edx contains C. What we need for the - algorithm is C in all bytes of the dword. Avoid + /* At the moment %edx contains CHR. What we need for the + algorithm is CHR in all bytes of the dword. Avoid operations on 16 bit words because these require an prefix byte (and one more cycle). */ movb %dl, %dh /* now it is 0|0|c|c */ @@ -108,9 +110,9 @@ ENTRY (__strchrnul) into bit 32 (=carry flag), so all of the hole bits will be changed. - 3) But wait! Aren't we looking for C, not zero? + 3) But wait! Aren't we looking for CHR, not zero? Good point. So what we do is XOR LONGWORD with a longword, - each of whose bytes is C. This turns each byte that is C + each of whose bytes is CHR. This turns each byte that is CHR into a zero. */ /* Each round the main loop processes 16 bytes. */ @@ -125,7 +127,7 @@ L(11): movl (%eax), %ecx /* get word (= 4 bytes) in question */ movl $0xfefefeff, %edi /* magic value */ addl %ecx, %edi /* add the magic value to the word. We get carry bits reported for each byte which - is *not* C */ + is *not* CHR */ /* According to the algorithm we had to reverse the effect of the XOR first and then test the overflow bits. But because the @@ -144,7 +146,7 @@ L(11): movl (%eax), %ecx /* get word (= 4 bytes) in question */ incl %edi /* add 1: if one carry bit was *not* set the addition will not result in 0. */ - /* If at least one byte of the word is C we don't get 0 in %edi. */ + /* If at least one byte of the word is CHR we don't get 0 in %edi. */ jnz L(7) /* found it => return pointer */ /* Now we made sure the dword does not contain the character we are @@ -169,8 +171,8 @@ L(11): movl (%eax), %ecx /* get word (= 4 bytes) in question */ movl $0xfefefeff, %edi /* magic value */ addl %ecx, %edi /* add the magic value to the word. We get carry bits reported for each byte which - is *not* C */ - jnc L(71) /* highest byte is C => return pointer */ + is *not* CHR */ + jnc L(71) /* highest byte is CHR => return pointer */ xorl %ecx, %edi /* ((word^charmask)+magic)^(word^charmask) */ orl $0xfefefeff, %edi /* set all non-carry bits */ incl %edi /* add 1: if one carry bit was *not* set @@ -194,8 +196,8 @@ L(11): movl (%eax), %ecx /* get word (= 4 bytes) in question */ movl $0xfefefeff, %edi /* magic value */ addl %ecx, %edi /* add the magic value to the word. We get carry bits reported for each byte which - is *not* C */ - jnc L(72) /* highest byte is C => return pointer */ + is *not* CHR */ + jnc L(72) /* highest byte is CHR => return pointer */ xorl %ecx, %edi /* ((word^charmask)+magic)^(word^charmask) */ orl $0xfefefeff, %edi /* set all non-carry bits */ incl %edi /* add 1: if one carry bit was *not* set @@ -219,8 +221,8 @@ L(11): movl (%eax), %ecx /* get word (= 4 bytes) in question */ movl $0xfefefeff, %edi /* magic value */ addl %ecx, %edi /* add the magic value to the word. We get carry bits reported for each byte which - is *not* C */ - jnc L(73) /* highest byte is C => return pointer */ + is *not* CHR */ + jnc L(73) /* highest byte is CHR => return pointer */ xorl %ecx, %edi /* ((word^charmask)+magic)^(word^charmask) */ orl $0xfefefeff, %edi /* set all non-carry bits */ incl %edi /* add 1: if one carry bit was *not* set @@ -246,20 +248,20 @@ L(71): addl $4, %eax But we have to take care of the case that a NUL char is found before this in the dword. */ -L(7): testb %cl, %cl /* is first byte C? */ +L(7): testb %cl, %cl /* is first byte CHR? */ jz L(6) /* yes => return pointer */ cmpb %dl, %cl /* is first byte NUL? */ je L(6) /* yes => return NULL */ incl %eax /* it's not in the first byte */ - testb %ch, %ch /* is second byte C? */ + testb %ch, %ch /* is second byte CHR? */ jz L(6) /* yes => return pointer */ cmpb %dl, %ch /* is second byte NUL? */ je L(6) /* yes => return NULL? */ incl %eax /* it's not in the second byte */ shrl $16, %ecx /* make upper byte accessible */ - testb %cl, %cl /* is third byte C? */ + testb %cl, %cl /* is third byte CHR? */ jz L(6) /* yes => return pointer */ cmpb %dl, %cl /* is third byte NUL? */ je L(6) /* yes => return NULL */ @@ -269,7 +271,8 @@ L(7): testb %cl, %cl /* is first byte C? */ L(6): popl %edi /* restore saved register content */ - ret + LEAVE + RET_PTR END (__strchrnul) weak_alias (__strchrnul, strchrnul) |