Add new fuzz binary.

fuzz/FuzzPaeth.cpp

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "Fuzz.h"
+
+// This really is just an example Fuzz*.cpp file.
+// It tests that two different ways of calculating the Paeth predictor function are equivalent.
+
+static uint8_t paeth_std(uint8_t a, uint8_t b, uint8_t c) {
+    int p = a+b-c;
+
+    int pa = abs(p-a),
+        pb = abs(p-b),
+        pc = abs(p-c);
+
+    if (pb < pa) { pa = pb; a = b; }
+    if (pc < pa) {          a = c; }
+    return a;
+}
+
+static uint8_t paeth_alt(uint8_t a, uint8_t b, uint8_t c) {
+    int min = SkTMin(a,b),
+        max = SkTMax(a,b);
+    int delta = (max-min)/3;
+
+    if (c <= min+delta) return max;
+    if (c >= max-delta) return min;
+    return c;
+}
+
+DEF_FUZZ(Paeth, fuzz) {
+    int a = fuzz->nextU(),
+        b = fuzz->nextU(),
+        c = fuzz->nextU();
+    ASSERT(paeth_alt(a,b,c) == paeth_std(a,b,c));
+}