Revert of Remove unused (by clients) SkUnitMapper (https://codereview.chromium.org/283273002/)

src/utils/SkUnitMappers.cpp

+
+/*
+ * Copyright 2011 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#include "SkUnitMappers.h"
+#include "SkReadBuffer.h"
+#include "SkWriteBuffer.h"
+
+
+SkDiscreteMapper::SkDiscreteMapper(int segments) {
+    if (segments < 2) {
+        fSegments = 0;
+        fScale = 0;
+    } else {
+        if (segments > 0xFFFF) {
+            segments = 0xFFFF;
+        }
+        fSegments = segments;
+        fScale = (1 << 30) / (segments - 1);
+    }
+}
+
+uint16_t SkDiscreteMapper::mapUnit16(uint16_t input) {
+    SkFixed x = input * fSegments >> 16;
+    x = x * fScale >> 14;
+    x += x << 15 >> 31; // map 0x10000 to 0xFFFF
+    return SkToU16(x);
+}
+
+SkDiscreteMapper::SkDiscreteMapper(SkReadBuffer& rb)
+        : SkUnitMapper(rb) {
+    fSegments = rb.readInt();
+    fScale = rb.read32();
+}
+
+void SkDiscreteMapper::flatten(SkWriteBuffer& wb) const {
+    this->INHERITED::flatten(wb);
+
+    wb.writeInt(fSegments);
+    wb.write32(fScale);
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+uint16_t SkCosineMapper::mapUnit16(uint16_t input)
+{
+    /*  we want to call cosine(input * pi/2) treating input as [0...1)
+        however, the straight multitply would overflow 32bits since input is
+        16bits and pi/2 is 17bits, so we shift down our pi const before we mul
+    */
+    SkFixed rads = (unsigned)(input * (SK_FixedPI >> 2)) >> 15;
+    SkFixed x = SkFixedCos(rads);
+    x += x << 15 >> 31; // map 0x10000 to 0xFFFF
+    return SkToU16(x);
+}
+
+SkCosineMapper::SkCosineMapper(SkReadBuffer& rb)
+    : SkUnitMapper(rb) {}