Add GrNextSizePow2

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4069

BUG=skia:5882

Change-Id: Ib9af5918716be594c3c07239eca179dbb4eb8566
Reviewed-on: https://skia-review.googlesource.com/4069
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>

src/core/SkMathPriv.h

@@ -154,6 +154,28 @@ static inline uint32_t GrNextPow2(uint32_t n) {
     return n ? (1 << (32 - SkCLZ(n - 1))) : 1;
 }
 
+/**
+ * Returns the next power of 2 >= n or n if the next power of 2 can't be represented by size_t.
+ */
+static inline size_t GrNextSizePow2(size_t n) {
+    constexpr int kNumSizeTBits = 8 * sizeof(size_t);
+    constexpr size_t kHighBitSet = size_t(1) << (kNumSizeTBits - 1);
+
+    if (!n) {
+        return 1;
+    } else if (n >= kHighBitSet) {
+        return n;
+    }
+
+    n--;
+    uint32_t shift = 1;
+    while (shift < kNumSizeTBits) {
+        n |= n >> shift;
+        shift <<= 1;
+    }
+    return n + 1;
+}
+
 static inline int GrNextPow2(int n) {
     SkASSERT(n >= 0); // this impl only works for non-neg.
     return n ? (1 << (32 - SkCLZ(n - 1))) : 1;

src/gpu/GrResourceProvider.cpp

@@ -109,8 +109,8 @@ GrBuffer* GrResourceProvider::createBuffer(size_t size, GrBufferType intendedTyp
     }
 
     // bin by pow2 with a reasonable min
-    static const uint32_t MIN_SIZE = 1 << 12;
-    size_t allocSize = SkTMax(MIN_SIZE, GrNextPow2(SkToUInt(size)));
+    static const size_t MIN_SIZE = 1 << 12;
+    size_t allocSize = SkTMax(MIN_SIZE, GrNextSizePow2(size));
 
     GrScratchKey key;
     GrBuffer::ComputeScratchKeyForDynamicVBO(allocSize, intendedType, &key);

tests/MathTest.cpp

@@ -685,3 +685,41 @@ DEF_TEST(divmod_s32, r) {
 DEF_TEST(divmod_s64, r) {
     test_divmod<int64_t>(r);
 }
+
+static void test_nextsizepow2(skiatest::Reporter* r, size_t test, size_t expectedAns) {
+    size_t ans = GrNextSizePow2(test);
+
+    REPORTER_ASSERT(r, ans == expectedAns);
+    //SkDebugf("0x%zx -> 0x%zx (0x%zx)\n", test, ans, expectedAns);
+}
+
+DEF_TEST(GrNextSizePow2, reporter) {
+    constexpr int kNumSizeTBits = 8 * sizeof(size_t);
+
+    size_t test = 0, expectedAns = 1;
+
+    test_nextsizepow2(reporter, test, expectedAns);
+
+    test = 1; expectedAns = 1;
+
+    for (int i = 1; i < kNumSizeTBits; ++i) {
+        test_nextsizepow2(reporter, test, expectedAns);
+
+        test++;
+        expectedAns <<= 1;
+
+        test_nextsizepow2(reporter, test, expectedAns);
+
+        test = expectedAns;
+    }
+
+    // For the remaining three tests there is no higher power (of 2)
+    test = 0x1;
+    test <<= kNumSizeTBits-1;
+    test_nextsizepow2(reporter, test, test);
+
+    test++;
+    test_nextsizepow2(reporter, test, test);
+
+    test_nextsizepow2(reporter, SIZE_MAX, SIZE_MAX);
+}