Implement optimal huffman encoding for (M)JPEG.

> seems to break
> make fate-vsynth1-mjpeg-444

Fixed.

2 files changed, 164 insertions, 0 deletions

diff --git a/libavcodec/tests/.gitignore b/libavcodec/tests/.gitignore
index 0ab029696d..f22ac821cb 100644
--- a/libavcodec/tests/.gitignore
+++ b/libavcodec/tests/.gitignore
@@ -10,6 +10,7 @@
 /imgconvert
 /jpeg2000dwt
 /mathops
+/mjpegenc_huffman
 /motion
 /options
 /rangecoder
diff --git a/libavcodec/tests/mjpegenc_huffman.c b/libavcodec/tests/mjpegenc_huffman.c
new file mode 100644
index 0000000000..4559cbe765
--- /dev/null
+++ b/libavcodec/tests/mjpegenc_huffman.c
@@ -0,0 +1,163 @@
+/*
+ * Copyright (c) 2016 William Ma, Sofia Kim, Dustin Woo
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * Optimal Huffman Encoding tests.
+ */
+
+#include "libavcodec/avcodec.h"
+#include <stdlib.h>
+#include "libavcodec/mjpegenc.h"
+#include "libavcodec/mjpegenc_huffman.h"
+#include "libavcodec/mjpegenc_common.h"
+#include "libavcodec/mpegvideo.h"
+
+// Validate the computed lengths satisfy the JPEG restrictions and is optimal.
+static int check_lengths(int L, int expected_length,
+                         const int *probs, int nprobs)
+{
+    HuffTable lengths[256];
+    PTable val_counts[256];
+    int actual_length = 0, i, j, k, prob, length;
+    int ret = 0;
+    double cantor_measure = 0;
+    assert(nprobs <= 256);
+
+    for (i = 0; i < nprobs; i++) {
+        val_counts[i] = (PTable){.value = i, .prob = probs[i]};
+    }
+
+    ff_mjpegenc_huffman_compute_bits(val_counts, lengths, nprobs, L);
+
+    for (i = 0; i < nprobs; i++) {
+        // Find the value's prob and length
+        for (j = 0; j < nprobs; j++)
+            if (val_counts[j].value == i) break;
+        for (k = 0; k < nprobs; k++)
+            if (lengths[k].code == i) break;
+        if (!(j < nprobs && k < nprobs)) return 1;
+        prob = val_counts[j].prob;
+        length = lengths[k].length;
+
+        if (prob) {
+            actual_length += prob * length;
+            cantor_measure += 1. / (1 << length);
+        }
+
+        if (length > L || length < 1) return 1;
+    }
+    // Check that the codes can be prefix-free.
+    if (cantor_measure > 1) ret = 1;
+    // Check that the total length is optimal
+    if (actual_length != expected_length) ret = 1;
+
+    if (ret == 1) {
+      fprintf(stderr,
+              "Cantor measure: %f\n"
+              "Actual length: %d\n"
+              "Expected length: %d\n",
+              cantor_measure, actual_length, expected_length);
+    }
+
+    return ret;
+}
+
+static const int probs_zeroes[] = {6, 6, 0, 0, 0};
+static const int probs_skewed[] = {2, 0, 0, 0, 0, 1, 0, 0, 20, 0, 2,
+    0, 10, 5, 1, 1, 9, 1, 1, 6, 0, 5, 0, 1, 0, 7, 6, 1, 1, 5, 0, 0, 0, 0,
+    11, 0, 0, 0, 51, 1, 0, 20, 0, 1, 0, 0, 0, 0, 6, 106, 1, 0, 1, 0, 2, 1,
+    16, 0, 0, 5, 0, 0, 0, 4, 3, 15, 4, 4, 0, 0, 0, 3, 0, 0, 1, 0, 3, 0, 3,
+    2, 2, 0, 0, 4, 3, 40, 1, 2, 0, 22, 0, 0, 0, 9, 0, 0, 0, 0, 1, 1, 0, 1,
+    6, 11, 4, 10, 28, 6, 1, 0, 0, 9, 9, 4, 0, 0, 0, 0, 8, 33844, 2, 0, 2,
+    1, 1, 5, 0, 0, 1, 9, 1, 0, 4, 14, 4, 0, 0, 3, 8, 0, 51, 9, 6, 1, 1, 2,
+    2, 3, 1, 5, 5, 29, 0, 0, 0, 0, 14, 29, 6, 4, 13, 12, 2, 3, 1, 0, 5, 4,
+    1, 1, 0, 0, 29, 1, 0, 0, 0, 0, 4, 0, 0, 1, 0, 1, 7, 0, 42, 0, 0, 0, 0,
+    0, 2, 0, 3, 9, 0, 0, 0, 2, 1, 0, 0, 6, 5, 6, 1, 2, 3, 0, 0, 0, 3, 0, 0,
+    28, 0, 2, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 23, 0, 0, 0, 0,
+    0, 21, 1, 0, 3, 24, 2, 0, 0, 7, 0, 0, 1, 5, 1, 2, 0, 5};
+static const int probs_sat[] = {74, 8, 14, 7, 9345, 40, 0, 2014, 2, 1,
+    115, 0, 2, 1, 194, 388, 20, 0, 0, 2, 1, 121, 1, 1583, 0, 16, 21, 2, 132,
+    2, 15, 9, 13, 1, 0, 2293, 2, 8, 5, 2, 30, 0, 0, 4, 54, 783, 4, 1, 2, 4,
+    0, 22, 93, 1, 143, 19, 0, 36, 32, 4, 6, 33, 3, 45, 0, 8, 1, 0, 18, 17, 1,
+    0, 1, 0, 0, 1, 1004, 38, 3, 8, 90, 23, 0, 2819, 3, 0, 970, 158, 9, 6, 4,
+    48, 4, 0, 1, 0, 0, 60, 3, 62, 0, 2, 2, 2, 279, 66, 16, 1, 20, 0, 7, 9,
+    32, 1411, 6, 3, 27, 1, 5, 49, 0, 0, 0, 0, 0, 2, 10, 1, 1, 2, 3, 801, 3,
+    25, 5, 1, 1, 0, 632, 0, 14, 18, 5, 8, 200, 4, 4, 22, 12, 0, 4, 1, 0, 2,
+    4, 9, 3, 16, 7, 2, 2, 213, 0, 2, 620, 39303, 0, 1, 0, 2, 1, 183781, 1,
+    0, 0, 0, 94, 7, 3, 4, 0, 4, 306, 43, 352, 76, 34, 13, 11, 0, 51, 1, 13,
+    19, 0, 26, 0, 7276, 4, 207, 31, 1, 2, 4, 6, 19, 8, 17, 4, 6, 0, 1085, 0,
+    0, 0, 3, 489, 36, 1, 0, 1, 9420, 294, 28, 0, 57, 5, 0, 9, 2, 0, 1, 2, 2,
+    0, 0, 9, 2, 29, 2, 2, 7, 0, 5, 490, 0, 7, 5, 0, 1, 8, 0, 0, 23255, 0, 1};
+
+// Test the example given on @see
+// http://guru.multimedia.cx/small-tasks-for-ffmpeg/
+int main(int argc, char **argv)
+{
+    int i, ret = 0;
+    // Probabilities of symbols 0..4
+    static PTable val_counts[] = {
+        {.value = 0, .prob = 1},
+        {.value = 1, .prob = 2},
+        {.value = 2, .prob = 5},
+        {.value = 3, .prob = 10},
+        {.value = 4, .prob = 21},
+    };
+    // Expected code lengths for each symbol
+    static const HuffTable expected[] = {
+        {.code = 0, .length = 3},
+        {.code = 1, .length = 3},
+        {.code = 2, .length = 3},
+        {.code = 3, .length = 3},
+        {.code = 4, .length = 1},
+    };
+    // Actual code lengths
+    HuffTable distincts[5];
+
+    // Build optimal huffman tree using an internal function, to allow for
+    // smaller-than-normal test cases. This mutates val_counts by sorting.
+    ff_mjpegenc_huffman_compute_bits(val_counts, distincts,
+                                     FF_ARRAY_ELEMS(distincts), 3);
+
+    for (i = 0; i < FF_ARRAY_ELEMS(distincts); i++) {
+        if (distincts[i].code != expected[i].code ||
+            distincts[i].length != expected[i].length) {
+            fprintf(stderr,
+                    "Built huffman does not equal expectations. "
+                    "Expected: code %d probability %d, "
+                    "Actual: code %d probability %d\n",
+                    expected[i].code, expected[i].length,
+                    distincts[i].code, distincts[i].length);
+            ret = 1;
+        }
+    }
+
+    // Check handling of zero probabilities
+    if (check_lengths(16, 18, probs_zeroes, FF_ARRAY_ELEMS(probs_zeroes)))
+        ret = 1;
+    // Check skewed distribution over 256 without saturated lengths
+    if (check_lengths(16, 41282, probs_skewed, FF_ARRAY_ELEMS(probs_skewed)))
+        ret = 1;
+    // Check skewed distribution over 256 with saturated lengths
+    if (check_lengths(16, 669904, probs_sat, FF_ARRAY_ELEMS(probs_sat)))
+        ret = 1;
+
+    return ret;
+}