Roll skia/third_party/skcms d931999c3afd..6655095842ec (1 commits)

Also whitelist third_party/skcms from #include rewrites.

https://skia.googlesource.com/skcms.git/+log/d931999c3afd..6655095842ec

git log d931999c3afd..6655095842ec --date=short --no-merges --format='%ad %ae %s'
2019-08-20 mtklein@google.com Add missing b-tweak to skcms_TF_Invert()

Created with:
  gclient setdep -r skia/third_party/skcms@6655095842ec

The AutoRoll server is located here: https://autoroll.skia.org/r/skcms-skia-autoroll

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff, who should
be CC'd on the roll, and stop the roller if necessary.

CQ_INCLUDE_TRYBOTS=luci.chromium.try:linux-blink-rel

Bug: chromium:976551
Change-Id: I6566968525070f0af808d04211b16e71f9850cea
TBR=egdaniel@google.com,mtklein@google.com
TBR=egdaniel@google.com,mtklein@google.com

Change-Id: I2c9b6a270693e9e93303b9cfef1262488bba1aae
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/235936
Commit-Queue: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>

third_party/skcms/skcms.cc

@@ -266,6 +266,11 @@ static bool tf_is_valid(const skcms_TransferFunction* tf) {
         return false;
     }
 
+    // It's rather _complex_ to raise a negative number to a fractional power tf->g.
+    if (tf->a * tf->d + tf->b < 0) {
+        return false;
+    }
+
     return true;
 }
 
@@ -1404,6 +1409,7 @@ static float exp2f_(float x) {
 }
 
 float powf_(float x, float y) {
+    assert (x >= 0);
     return (x == 0) || (x == 1) ? x
                                 : exp2f_(log2f_(x) * y);
 }
@@ -1468,6 +1474,17 @@ bool skcms_TransferFunction_invert(const skcms_TransferFunction* src, skcms_Tran
     inv.b = -k * src->e;
     inv.e = -src->b / src->a;
 
+    // We need to enforce the same constraints here that we do when fitting a curve,
+    // a >= 0 and ad+b >= 0.  These constraints are checked by tf_is_valid(), so they're true
+    // of the source function if we're here.  And if the source a >= 0, inv.a definitely is too.
+    assert (inv.a >= 0);
+
+    // On the other hand our ad+b could have gone slightly negative here.  Tweak inv.b if needed.
+    if (inv.a * inv.d + inv.b < 0) {
+        inv.b = -inv.a * inv.d;
+    }
+    assert (inv.a * inv.d + inv.b >= 0);
+
     // Now in principle we're done.
     // But to preserve the valuable invariant inv(src(1.0f)) == 1.0f,
     // we'll tweak e.  These two values should be close to each other,
@@ -1663,6 +1680,9 @@ static bool fit_nonlinear(const skcms_Curve* curve, int L, int N, skcms_Transfer
         P[2] = -P[1] * tf->d;
     }
 
+    assert (P[1] >= 0 &&
+            P[1] * tf->d + P[2] >= 0);
+
     tf->g = P[0];
     tf->a = P[1];
     tf->b = P[2];

third_party/skcms/version.sha1

@@ -1 +1 @@
-d931999c3afd98880d3f366e12f858824be44fba
+6655095842ecdc56e1ab5507646dedd241e13d8b

tools/rewrite_includes.py

@@ -69,7 +69,7 @@ def to_rewrite():
 # Rewrite any #includes relative to Skia's top-level directory.
 need_rewriting = []
 for file_path in to_rewrite():
-  if 'generated' in file_path:
+  if 'generated' in file_path or 'third_party/skcms' in file_path:
     continue
   if (file_path.endswith('.h') or
       file_path.endswith('.c') or