Roll skia/third_party/skcms 5cc905d..e4c0e54 (1 commits)

https://skia.googlesource.com/skcms.git/+log/5cc905d..e4c0e54

2018-05-16 brianosman@google.com Add lerping to skcms_eval_curve


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CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel
TBR=herb@google.com

Change-Id: Ie44a66826197489e499a2ce7dcbba8592a43973f
Reviewed-on: https://skia-review.googlesource.com/128650
Reviewed-by: skcms-skia-autoroll <skcms-skia-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Commit-Queue: skcms-skia-autoroll <skcms-skia-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>

2 files changed, 24 insertions, 13 deletions

diff --git a/third_party/skcms/src/Curve.c b/third_party/skcms/src/Curve.c
index f52eb983fe..2b5a042500 100644
--- a/third_party/skcms/src/Curve.c
+++ b/third_party/skcms/src/Curve.c
@@ -10,25 +10,36 @@
 #include "TransferFunction.h"
 #include <assert.h>
 
+static float minus_1_ulp(float x) {
+    int32_t bits;
+    memcpy(&bits, &x, sizeof(bits));
+    bits = bits - 1;
+    memcpy(&x, &bits, sizeof(bits));
+    return x;
+}
+
 float skcms_eval_curve(const skcms_Curve* curve, float x) {
     if (curve->table_entries == 0) {
         return skcms_TransferFunction_eval(&curve->parametric, x);
     }
 
-    // TODO: today we should always hit an entry exactly, but if that changes, lerp?
-    // (We add half to account for slight int -> float -> int round tripping issues.)
-    float fx = x*(curve->table_entries - 1);
-    int ix = (int)( fx + 0.5f );
-
-    assert ( fabsf_(fx - (float)ix) < 0.0005 );
+    float ix = fmaxf_(0, fminf_(x, 1)) * (curve->table_entries - 1);
+    int   lo = (int)            ix,
+          hi = (int)minus_1_ulp(ix + 1.0f);
+    float t = ix - (float)lo;
 
+    float l, h;
     if (curve->table_8) {
-        return curve->table_8[ix] * (1/255.0f);
+        l = curve->table_8[lo] * (1/255.0f);
+        h = curve->table_8[hi] * (1/255.0f);
     } else {
-        uint16_t be;
-        memcpy(&be, curve->table_16 + 2*ix, 2);
-
-        uint16_t le = ((be << 8) | (be >> 8)) & 0xffff;
-        return le * (1/65535.0f);
+        uint16_t be_l, be_h;
+        memcpy(&be_l, curve->table_16 + 2*lo, 2);
+        memcpy(&be_h, curve->table_16 + 2*hi, 2);
+        uint16_t le_l = ((be_l << 8) | (be_l >> 8)) & 0xffff;
+        uint16_t le_h = ((be_h << 8) | (be_h >> 8)) & 0xffff;
+        l = le_l * (1/65535.0f);
+        h = le_h * (1/65535.0f);
     }
+    return l + (h-l)*t;
 }
diff --git a/third_party/skcms/version.sha1 b/third_party/skcms/version.sha1
index 14bc5efe03..a2c36d6635 100755
--- a/third_party/skcms/version.sha1
+++ b/third_party/skcms/version.sha1
@@ -1 +1 @@
-5cc905db968da1cad33f473f2d7700972bb959a1
\ No newline at end of file
+e4c0e54a9c1998286f0d4760a71f42ae23679541
\ No newline at end of file