85 lines
2.9 KiB
C
85 lines
2.9 KiB
C
/****************************************************************************
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* libs/libc/unistd/lib_swab.c
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <sys/types.h>
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#include <unistd.h>
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#include <assert.h>
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: swab
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*
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* Description:
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* The swab() function will copy nbytes bytes, which are pointed to by
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* 'src', to the object pointed to by 'dest', exchanging adjacent bytes.
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* The 'nbytes' argument should be even. If 'nbytes' is odd, swab() copies
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* and exchanges 'nbytes'-1 bytes and the disposition of the last byte is
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* unspecified. If copying takes place between objects that overlap, the
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* behavior is undefined. If nbytes is negative, swab() does nothing.
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*
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* Returned Value:
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* None
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*
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****************************************************************************/
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void swab(FAR const void *src, FAR void *dest, ssize_t nbytes)
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{
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FAR const uint8_t *src8 = (FAR const uint8_t *)src;
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FAR uint8_t *dest8 = (FAR uint8_t *)dest;
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FAR uint8_t *end8;
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DEBUGASSERT(src != NULL && dest != NULL);
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/* Do nother if nbytes is negative or it there are few then 2 bytes to be
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* transferred.
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*/
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if (nbytes > 1)
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{
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/* The end of dest buffer + 1 byte (skipping any odd numbered byte at
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* the end of the buffer.
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*/
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end8 = dest8 + (nbytes & ~1);
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/* Loop until the destination is equal to the end + 1 address */
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while (dest8 != end8)
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{
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register uint8_t tmp;
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/* Transfer the bytes, swapping the order */
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tmp = *src8++;
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*dest8++ = *src8++;
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*dest8++ = tmp;
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}
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}
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}
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