104 lines
2.1 KiB
C
104 lines
2.1 KiB
C
/*
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swap_bytes: Swap byte order of samples in a buffer.
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copyright 2018 by the mpg123 project
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licensed under the terms of the LGPL 2.1
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see COPYING and AUTHORS files in distribution or http://mpg123.org
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initially written by Thomas Orgis
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This is C source to include in your code to get the function named
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swap_bytes. It is serves intentional duplication in libmpg123 and
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libsyn123 to avoid introducing a dependency between them. This function
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is too small for that.
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*/
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/* Other headers are already included! */
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/* Optionally use platform-specific byteswap macros. */
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#ifdef HAVE_BYTESWAP_H
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#include <byteswap.h>
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#endif
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/* Plain stupid swapping of elements in a byte array. */
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/* This is the fallback when there is no native bswap macro. */
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#define SWAP(a,b) tmp = p[a]; p[a] = p[b]; p[b] = tmp;
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/* Convert samplecount elements of samplesize bytes each in buffer buf. */
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static void swap_bytes(void *buf, size_t samplesize, size_t samplecount)
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{
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unsigned char *p = buf;
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unsigned char *pend = (unsigned char*)buf+samplesize*samplecount;
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unsigned char tmp;
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if(samplesize < 2)
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return;
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switch(samplesize)
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{
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case 2: /* AB -> BA */
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#ifdef HAVE_BYTESWAP_H
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{
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uint16_t* pp = (uint16_t*)p;
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for(; pp<(uint16_t*)pend; ++pp)
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*pp = bswap_16(*pp);
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}
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#else
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for(; p<pend; p+=2)
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{
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SWAP(0,1)
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}
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#endif
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break;
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case 3: /* ABC -> CBA */
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for(; p<pend; p+=3)
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{
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SWAP(0,2)
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}
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break;
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case 4: /* ABCD -> DCBA */
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#ifdef HAVE_BYTESWAP_H
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{
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uint32_t* pp = (uint32_t*)p;
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for(; pp<(uint32_t*)pend; ++pp)
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*pp = bswap_32(*pp);
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}
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#else
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for(; p<pend; p+=4)
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{
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SWAP(0,3)
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SWAP(1,2)
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}
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#endif
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break;
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case 8: /* ABCDEFGH -> HGFEDCBA */
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#ifdef HAVE_BYTESWAP_H
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{
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uint64_t* pp = (uint64_t*)p;
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for(; pp<(uint64_t*)pend; ++pp)
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*pp = bswap_64(*pp);
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}
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#else
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for(; p<pend; p+=8)
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{
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SWAP(0,7)
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SWAP(1,6)
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SWAP(2,5)
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SWAP(3,4)
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}
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#endif
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break;
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/* All the weird choices with the full nested loop. */
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default:
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for(; p<pend; p+=samplesize)
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{
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size_t j;
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for(j=0; j<samplesize/2; ++j)
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{
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SWAP(j, samplesize-j-1)
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}
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}
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}
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}
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#undef SWAP
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