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Code Issues Releases Activity

libavutil: add av_lfg_init_from_data() function

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seeds an AVLFG from binary data.

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
This commit is contained in:
Jonathan Campbell 2016-09-03 03:29:29 -07:00 committed by Michael Niedermayer
parent 0a5add45c7
commit 76c5a69e26
4 changed files with 40 additions and 1 deletions
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3
doc/APIchanges
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@ -15,6 +15,9 @@ libavutil: 2015-08-28
API changes, most recent first:
2017-01-22 - xxxxxxx - lavu 55.44.100 - lfg.h
Add av_lfg_init_from_data().
2017-01-xx - xxxxxxx - lavc 57.74.100 - vaapi.h
Deprecate struct vaapi_context and the vaapi.h installed header.
Callers should set AVCodecContext.hw_frames_ctx instead.

27
libavutil/lfg.c
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@ -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;
}

9
libavutil/lfg.h
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@ -22,6 +22,8 @@
#ifndef AVUTIL_LFG_H
#define AVUTIL_LFG_H
#include <stdint.h>
typedef struct AVLFG {
unsigned int state[64];
int index;
@ -29,6 +31,13 @@ typedef struct AVLFG {
void av_lfg_init(AVLFG *c, unsigned int seed);
/**
* Seed the state of the ALFG using binary data.
*
* Return value: 0 on success, negative value (AVERROR) on failure.
*/
int av_lfg_init_from_data(AVLFG *c, const uint8_t *data, unsigned int length);
/**
* Get the next random unsigned 32-bit number using an ALFG.
*

2
libavutil/version.h
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@ -79,7 +79,7 @@
*/
#define LIBAVUTIL_VERSION_MAJOR 55
#define LIBAVUTIL_VERSION_MINOR 43
#define LIBAVUTIL_VERSION_MINOR 44
#define LIBAVUTIL_VERSION_MICRO 100
#define LIBAVUTIL_VERSION_INT AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \