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Diffstat (limited to 'lib/libc/i386/string/swab.S')
| -rw-r--r-- | lib/libc/i386/string/swab.S | 99 |
1 files changed, 99 insertions, 0 deletions
diff --git a/lib/libc/i386/string/swab.S b/lib/libc/i386/string/swab.S new file mode 100644 index 0000000..80b2f3c --- /dev/null +++ b/lib/libc/i386/string/swab.S @@ -0,0 +1,99 @@ +/* + * Copyright (c) 1993,94 Winning Strategies, Inc. + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * 3. All advertising materials mentioning features or use of this software + * must display the following acknowledgement: + * This product includes software developed by Winning Strategies, Inc. + * 4. The name of the author may not be used to endorse or promote products + * derived from this software without specific prior written permission + * + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR + * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES + * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. + * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT + * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, + * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF + * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + */ + +#include <machine/asm.h> +__FBSDID("$FreeBSD$"); + +/* + * void + * swab (const void *src, void *dst, size_t len) + * copy len bytes from src to dst, swapping adjacent bytes + * + * On the i486, this code is negligibly faster than the code generated + * by gcc at about half the size. If my i386 databook is correct, it + * should be considerably faster than the gcc code on an i386. + * + * Written by: + * J.T. Conklin (jtc@wimsey.com), Winning Strategies, Inc. + */ + +ENTRY(swab) + pushl %esi + pushl %edi + movl 12(%esp),%esi + movl 16(%esp),%edi + movl 20(%esp),%ecx + + cld # set direction forward + + shrl $1,%ecx + testl $7,%ecx # copy first group of 1 to 7 words + jz L2 # while swaping alternate bytes. + .align 2,0x90 +L1: lodsw + rorw $8,%ax + stosw + decl %ecx + testl $7,%ecx + jnz L1 + +L2: shrl $3,%ecx # copy remainder 8 words at a time + jz L4 # while swapping alternate bytes. + .align 2,0x90 +L3: lodsw + rorw $8,%ax + stosw + lodsw + rorw $8,%ax + stosw + lodsw + rorw $8,%ax + stosw + lodsw + rorw $8,%ax + stosw + lodsw + rorw $8,%ax + stosw + lodsw + rorw $8,%ax + stosw + lodsw + rorw $8,%ax + stosw + lodsw + rorw $8,%ax + stosw + decl %ecx + jnz L3 + +L4: popl %edi + popl %esi + ret |
