diff options
author | Jonathan Campbell <jonathan@castus.tv> | 2016-09-03 03:29:29 -0700 |
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committer | Michael Niedermayer <michael@niedermayer.cc> | 2017-01-22 02:28:53 +0100 |
commit | 76c5a69e26afbfdfc5b6f538594ea12efa31fc9a (patch) | |
tree | 0cef85bf008e1670513082029c727a5b38cc3979 /libavutil/lfg.c | |
parent | 0a5add45c7527bbe627899be744f962588e5b2fa (diff) | |
download | ffmpeg-76c5a69e26afbfdfc5b6f538594ea12efa31fc9a.tar.gz |
libavutil: add av_lfg_init_from_data() function
seeds an AVLFG from binary data.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
Diffstat (limited to 'libavutil/lfg.c')
-rw-r--r-- | libavutil/lfg.c | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/libavutil/lfg.c b/libavutil/lfg.c index 08a4f678e2..46b04d2403 100644 --- a/libavutil/lfg.c +++ b/libavutil/lfg.c @@ -23,7 +23,9 @@ #include <limits.h> #include <math.h> #include "lfg.h" +#include "crc.h" #include "md5.h" +#include "error.h" #include "intreadwrite.h" #include "attributes.h" @@ -58,3 +60,28 @@ void av_bmg_get(AVLFG *lfg, double out[2]) out[0] = x1 * w; out[1] = x2 * w; } + +int av_lfg_init_from_data(AVLFG *c, const uint8_t *data, unsigned int length) { + unsigned int beg, end, segm; + const AVCRC *avcrc; + uint32_t crc = 1; + + /* avoid integer overflow in the loop below. */ + if (length > (UINT_MAX / 128U)) return AVERROR(EINVAL); + + c->index = 0; + avcrc = av_crc_get_table(AV_CRC_32_IEEE); /* This can't fail. It's a well-defined table in crc.c */ + + /* across 64 segments of the incoming data, + * do a running crc of each segment and store the crc as the state for that slot. + * this works even if the length of the segment is 0 bytes. */ + beg = 0; + for (segm = 0;segm < 64;segm++) { + end = (((segm + 1) * length) / 64); + crc = av_crc(avcrc, crc, data + beg, end - beg); + c->state[segm] = (unsigned int)crc; + beg = end; + } + + return 0; +} |