Update external/libyuv to r1837

Update external/libyuv to version r1837 (d53f1bee) from upstream.

This brings in some new functions that will be used by libavif.

Also update README.version with local modifications. The files/
subdirectory is a pristine copy of the upstream checkout except
for the local modifications that are listed in README.version.

Bug: b/241008246
Bug: b/228492909
Test: Builds. Media and Camera CTS tests pass.
Merged-In: I1bd041e475666e13fafd8c3792d7142a022d435a
Change-Id: I85df21181e582ff835aab1e9ef13ad3ac8421d30

1 files changed, 105 insertions, 0 deletions

diff --git a/files/util/yuvconstants.c b/files/util/yuvconstants.c
new file mode 100644
index 00000000..037e0824
--- /dev/null
+++ b/files/util/yuvconstants.c
@@ -0,0 +1,105 @@
+/*
+ *  Copyright 2021 The LibYuv Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS. All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+// This utility computes values needed to generate yuvconstants based on
+// white point values.
+// The yuv formulas are tuned for 8 bit YUV channels.
+
+// See Also
+// https://mymusing.co/bt601-yuv-to-rgb-conversion-color/
+
+// BT.709 full range YUV to RGB reference
+//  R = Y               + V * 1.5748
+//  G = Y - U * 0.18732 - V * 0.46812
+//  B = Y + U * 1.8556
+//  KR = 0.2126
+//  KB = 0.0722
+
+// // Y contribution to R,G,B.  Scale and bias.
+// #define YG 16320 /* round(1.000 * 64 * 256 * 256 / 257) */
+// #define YB 32    /* 64 / 2 */
+//
+// // U and V contributions to R,G,B.
+// #define UB 113 /* round(1.77200 * 64) */
+// #define UG 22  /* round(0.34414 * 64) */
+// #define VG 46  /* round(0.71414 * 64) */
+// #define VR 90  /* round(1.40200 * 64) */
+//
+// // Bias values to round, and subtract 128 from U and V.
+// #define BB (-UB * 128 + YB)
+// #define BG (UG * 128 + VG * 128 + YB)
+// #define BR (-VR * 128 + YB)
+
+int main(int argc, const char* argv[]) {
+  if (argc < 2) {
+    printf("yuvconstants Kr Kb\n");
+    printf("  MC BT          KR = 0.2126; KB = 0.0722\n");
+    printf("  1  BT.709      KR = 0.2126; KB = 0.0722\n");
+    printf("  4  FCC         KR = 0.30;   KB = 0.11\n");
+    printf("  6  BT.601      KR = 0.299;  KB = 0.114\n");
+    printf("  7  SMPTE 240M  KR = 0.212;  KB = 0.087\n");
+    printf("  9  BT.2020     KR = 0.2627; KB = 0.0593\n");
+    return -1;
+  }
+  float kr = atof(argv[1]);
+  float kb = atof(argv[2]);
+  float kg = 1 - kr - kb;
+
+  float vr = 2 * (1 - kr);
+  float ug = 2 * ((1 - kb) * kb / kg);
+  float vg = 2 * ((1 - kr) * kr / kg);
+  float ub = 2 * (1 - kb);
+
+  printf("Full range\n");
+  printf("R = Y                + V * %5f\n", vr);
+  printf("G = Y - U * %6f - V * %6f\n", ug, vg);
+  printf("B = Y + U * %5f\n", ub);
+
+  printf("KR = %4f; ", kr);
+  printf("KB = %4f\n", kb);
+  // printf("KG = %4f\n", kg);
+  // #define YG 16320 /* round(1.000 * 64 * 256 * 256 / 257) */
+  // #define YB 32    /* 64 / 2 */
+  //
+  // // U and V contributions to R,G,B.
+
+  printf("UB %-3.0f /* round(%f * 64 = %8.4f) */\n", round(ub * 64), ub, ub * 64);
+  printf("UG %-3.0f /* round(%f * 64 = %8.4f) */\n", round(ug * 64), ug, ug * 64);
+  printf("VG %-3.0f /* round(%f * 64 = %8.4f) */\n", round(vg * 64), vg, vg * 64);
+  printf("VR %-3.0f /* round(%f * 64 = %8.4f) */\n", round(vr * 64), vr, vr * 64);
+
+  vr = 255.f / 224.f * 2 * (1 - kr);
+  ug = 255.f / 224.f * 2 * ((1 - kb) * kb / kg);
+  vg = 255.f / 224.f * 2 * ((1 - kr) * kr / kg);
+  ub = 255.f / 224.f * 2 * (1 - kb);
+
+  printf("\nLimited range\n");
+  printf("R = (Y - 16) * 1.164                + V * %5f\n", vr);
+  printf("G = (Y - 16) * 1.164 - U * %6f - V * %6f\n", ug, vg);
+  printf("B = (Y - 16) * 1.164 + U * %5f\n", ub);
+
+  // printf("KG = %4f\n", kg);
+  // #define YG 16320 /* round(1.000 * 64 * 256 * 256 / 257) */
+  // #define YB 32    /* 64 / 2 */
+  //
+  // // U and V contributions to R,G,B.
+
+  printf("UB %-3.0f /* round(%f * 64 = %8.4f) */\n", round(ub * 64), ub, ub * 64);
+  printf("UG %-3.0f /* round(%f * 64 = %8.4f) */\n", round(ug * 64), ug, ug * 64);
+  printf("VG %-3.0f /* round(%f * 64 = %8.4f) */\n", round(vg * 64), vg, vg * 64);
+  printf("VR %-3.0f /* round(%f * 64 = %8.4f) */\n", round(vr * 64), vr, vr * 64);
+
+  return 0;
+}