[FFmpeg-cvslog] libavutil: add av_lfg_init_from_data() function

Jonathan Campbell git at videolan.org
Sun Jan 22 03:31:01 EET 2017


ffmpeg | branch: master | Jonathan Campbell <jonathan at castus.tv> | Sat Sep  3 03:29:29 2016 -0700| [76c5a69e26afbfdfc5b6f538594ea12efa31fc9a] | committer: Michael Niedermayer

libavutil: add av_lfg_init_from_data() function

seeds an AVLFG from binary data.

Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=76c5a69e26afbfdfc5b6f538594ea12efa31fc9a
---

 doc/APIchanges      |  3 +++
 libavutil/lfg.c     | 27 +++++++++++++++++++++++++++
 libavutil/lfg.h     |  9 +++++++++
 libavutil/version.h |  2 +-
 4 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/doc/APIchanges b/doc/APIchanges
index 98f8076..f5f7e0c 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -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.
diff --git a/libavutil/lfg.c b/libavutil/lfg.c
index 08a4f67..46b04d2 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;
+}
diff --git a/libavutil/lfg.h b/libavutil/lfg.h
index ec90562..03f779a 100644
--- a/libavutil/lfg.h
+++ b/libavutil/lfg.h
@@ -22,6 +22,8 @@
 #ifndef AVUTIL_LFG_H
 #define AVUTIL_LFG_H
 
+#include <stdint.h>
+
 typedef struct AVLFG {
     unsigned int state[64];
     int index;
@@ -30,6 +32,13 @@ 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.
  *
  * Please also consider a simple LCG like state= state*1664525+1013904223,
diff --git a/libavutil/version.h b/libavutil/version.h
index 9f8c4c2..2e83ef2 100644
--- a/libavutil/version.h
+++ b/libavutil/version.h
@@ -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, \



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