Rockbox open source high quality audio player as a Music Player Daemon
mpris
rockbox
mpd
libadwaita
audio
rust
zig
deno
rockbox: add a crc32 reverse polynomial function
This uses the reverse of the polynomial used by the current crc_32
function. The code for this was derived from the implementation used
by tinf. This version is space optimized and should be a good way to
reduce code duplication in other parts of rockbox that use the same
crc32 algorithm. This is mainly of use in areas where DEFLATE is in
use.
Change-Id: I918da5b4ea4dc441c0e7e6b5007abcc2da463bcb
+33
+1
apps/plugin.c
+1
apps/plugin.c
+1
apps/plugin.h
+1
apps/plugin.h
+30
firmware/common/crc32.c
+30
firmware/common/crc32.c
···
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return crc32;
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}
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+
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/* crc_32r (derived from tinf crc32 which was taken from zlib)
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* CRC32 algorithm taken from the zlib source, which is
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* Copyright (C) 1995-1998 Jean-loup Gailly and Mark Adler
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*/
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/* Tool function to calculate a CRC32 (reversed polynomial) across some buffer */
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/* third argument is either the starting value or value from last piece */
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uint32_t crc_32r(const void *src, uint32_t len, uint32_t crc32)
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{
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const unsigned char* buf = src;
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/* reversed polynomial from other crc32 function -- 0xEDB88320 */
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static const unsigned crc32_lookup[16] =
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{
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0x00000000, 0x1DB71064, 0x3B6E20C8, 0x26D930AC,
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0x76DC4190, 0x6B6B51F4, 0x4DB26158, 0x5005713C,
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0xEDB88320, 0xF00F9344, 0xD6D6A3E8, 0xCB61B38C,
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0x9B64C2B0, 0x86D3D2D4, 0xA00AE278, 0xBDBDF21C
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};
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for(uint32_t i = 0; i < len; i++)
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{
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crc32 ^= buf[i];
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crc32 = crc32_lookup[crc32 & 0x0F] ^ (crc32 >> 4);
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crc32 = crc32_lookup[crc32 & 0x0F] ^ (crc32 >> 4);
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}
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return crc32;
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}